Condensed Matter
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New submissions for Fri, 27 Mar 20
 [1] arXiv:2003.11553 [pdf, other]

Title: Absolute anomalies in (2+1)D symmetryenriched topological states and exact (3+1)D constructionsComments: 39+18 pages, 20+13 figuresSubjects: Strongly Correlated Electrons (condmat.strel); High Energy Physics  Theory (hepth); Quantum Algebra (math.QA); Quantum Physics (quantph)
Certain patterns of symmetry fractionalization in (2+1)D topologically ordered phases of matter can be anomalous, which means that they possess an obstruction to being realized in purely (2+1)D. In this paper we demonstrate how to compute the anomaly for symmetryenriched topological (SET) states of bosons in complete generality. We demonstrate how, given any unitary modular tensor category (UMTC) and symmetry fractionalization class for a global symmetry group $G$, one can define a (3+1)D topologically invariant path integral in terms of a state sum for a $G$ symmetryprotected topological (SPT) state. We present an exactly solvable Hamiltonian for the system and demonstrate explicitly a (2+1)D $G$ symmetric surface termination that hosts deconfined anyon excitations described by the given UMTC and symmetry fractionalization class. We present concrete algorithms that can be used to compute anomaly indicators in general. Our approach applies to general symmetry groups, including anyonpermuting and antiunitary symmetries. In addition to providing a general way to compute the anomaly, our result also shows, by explicit construction, that every symmetry fractionalization class for any UMTC can be realized at the surface of a (3+1)D SPT state. As a byproduct, this construction also provides a way of explicitly seeing how the algebraic data that defines symmetry fractionalization in general arises in the context of exactly solvable models. In the case of unitary orientationpreserving symmetries, our results can also be viewed as providing a method to compute the $\mathcal{H}^4(G, U(1))$ obstruction that arises in the theory of $G$crossed braided tensor categories, for which no general method has been presented to date.
 [2] arXiv:2003.11559 [pdf, other]

Title: Excitonic fractional quantum Hall hierarchy in Moiré heterostructuresComments: 5+4 pages, 1+3 figuresSubjects: Strongly Correlated Electrons (condmat.strel); Mesoscale and Nanoscale Physics (condmat.meshall)
We consider fractional quantum Hall states in systems where two flat Chern number $C=\pm 1$ bands are labeled by an approximately conserved 'valley' index and interchanged by time reversal symmetry. At filling factor $\nu=1$ this setting admits an unusual hierarchy of correlated phases of excitons, neutral particlehole pair excitations of a fully valleypolarized `orbital ferromagnet' parent state where all electrons occupy a single valley. Excitons experience an effective magnetic field due to the Chern numbers of the underlying bands. This obstructs their condensation in favor of a variety of crystalline orders and gapped and gapless liquid states. All these have the same quantized charge Hall response and are electrically incompressible, but differ in their edge structure, orbital magnetization, and hence valley and thermal responses. We explore the relevance of this scenario for Moir\'e heterostructures of bilayer graphene on a hexagonal boron nitride substrate.
 [3] arXiv:2003.11560 [pdf, other]

Title: Exciton band topology in spontaneous quantum anomalous Hall insulators: applications to twisted bilayer grapheneComments: 5+11 pages, 2+2 figuresSubjects: Strongly Correlated Electrons (condmat.strel); Mesoscale and Nanoscale Physics (condmat.meshall)
We uncover topological features of neutral particlehole pair excitations of correlated quantum anomalous Hall (QAH) insulators whose approximately flat conduction and valence bands have equal and opposite nonzero Chern number. Using an exactly solvable model we show that the underlying band topology affects both the centerofmass and relative motion of particlehole bound states. This leads to the formation of topological exciton bands whose features are robust to nonuniformity of both the dispersion and the Berry curvature. We apply these ideas to recentlyreported brokensymmetry spontaneous QAH insulators in substrate aligned magicangle twisted bilayer graphene.
 [4] arXiv:2003.11564 [pdf, other]

Title: Environment assisted and environment hampered efficiency at maximum power in a molecular photo cellComments: submitted for publication, comments are welcomeSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Other Condensed Matter (condmat.other); Statistical Mechanics (condmat.statmech); Quantum Physics (quantph)
The molecular photo cell, i.e., a single molecule donoracceptor complex, beside being technologically important, is a paradigmatic example of a manybody system operating in strong nonequilibrium. The quantum transport and the photovoltaic energy conversion efficiency of the photocell, attached to two external leads, are investigated within the open quantum system approach by solving the Lindblad master equation. The interplay of the vibrational degrees of freedom corresponding to the molecules (via the electronphonon interaction) and the environment (via dephasing) shows its signature in the efficiency at maximum power. We find vibration assisted electron transport in the medium to strong electronphonon coupling regime when the system does not suffer dephasing. Exposure to dephasing hampers such a vibration assisted electron transport in a specific range of dephasing rate.
 [5] arXiv:2003.11569 [pdf]

Title: Crystal and magnetic structure of antiferromagnetic Mn$_{2}$PtPdSubjects: Materials Science (condmat.mtrlsci)
We have investigated the crystal and magnetic structure of Mn${}_{2}$PtPd alloy using powder xray and neutron diffraction experiments. This compound is believed to belong to the Heusler family having crystal symmetry $\mathit{I}$4/$\mathit{mmm}$ (TiAl${}_{3}$type). However, in this work we found that the Pd and Pt atoms are disordered and thus Mn${}_{2}$PtPd crystallizes in the $\mathit{L}$1${}_{0}$ structure having $\mathit{P}$4/$\mathit{mmm}$ symmetry (CuAuI type) like MnPt and MnPd binary alloys. The lattice constants are $\mathit{a}$ = 2.86 \r{A} and $\mathit{c}$ = 3.62 \r{A} at room temperature. Mn${}_{2}$PtPd has a collinear antiferromagnetic spin structure below the N\'{e}el temperature $\mathit{T}$${}_{N}$ = 866 K, where Mn moments of $\mathrm{\sim}$4 $\mu$${}_{B}$ lie in the $\mathit{ab}$plane. We observed a strong change in the lattice parameters near $\mathit{T}$${}_{N}$. The sample exhibits metallic behaviour, where electrical resistivity and carrier concentration are of the order of 10${}^{5}$ $\Omega$ cm and 10${}^{21}$ cm${}^{3}$, respectively.
 [6] arXiv:2003.11573 [pdf, other]

Title: Extracting nonFermi liquid fermionic selfenergy at $T=0$ from quantum Monte Carlo dataComments: 9 pages, 8 figuresSubjects: Strongly Correlated Electrons (condmat.strel); Statistical Mechanics (condmat.statmech); Superconductivity (condmat.suprcon)
Quantum Monte Carlo (QMC) simulations of correlated electron systems provide unbiased information about system behavior at a quantum critical point (QCP) and can verify or disprove the existing theories of nonFermi liquid (NFL) behavior at a QCP. However, simulations are carried out at a finite temperature, where quantumcritical features are masked by finite temperature effects. Here we present a method to rigorously separate thermal and quantum effects and extract the information about NFL physics at $T=0$. We demonstrate our method for a specific example of 2D fermions near a Isingferromagnetic QCP. We show that one can accurately extract from QMC data the zerotemperature form of fermionic selfenergy $\Sigma (\omega)$ even though the leading contribution to the selfenergy comes from thermal effects. We find that the frequency dependence of $\Sigma (\omega)$ agrees well with the analytic form obtained within the Eliashberg theory of dynamical quantum criticality, and obeys $\omega^{2/3}$ scaling at low frequencies. Our results open up a new avenue for QMC studies of quantumcritical metals.
 [7] arXiv:2003.11581 [pdf, other]

Title: Magnon Trap by Chiral Spin PumpingComments: 6 pages, 3 figuresSubjects: Mesoscale and Nanoscale Physics (condmat.meshall)
Chiral spin pumping is the generation of a unidirectional spin current in ferromagnetic films by dynamic dipolar stray fields from closeby nanomagnets. We formulate the theory of longrange chiral interactions between magnetic nanowires mediated by unidirectional spin waves in a magnetic film. We predict that two magnetic nanowires, of which one is actuated by microwaves, can trap spin waves. When both nanomagnets are excited by a uniform microwave, the interaction induced by the film magnons creates an imbalance in their magnon numbers.
 [8] arXiv:2003.11584 [pdf, ps, other]

Title: Experimental Determination of the Critical Spin Glass Correlation LengthComments: 5 pages, 5 figuresSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Disordered Systems and Neural Networks (condmat.disnn)
Measuring ThermoRemanent Magnetization (TRM) decays on a single crystal CuMn(6$\%$) spin glass sample, we have systematically mapped the rapid decrease of the characteristic timescale $tw_{eff}$ near $T_g$. Using $tw_{eff}$ to determine the length scale of the growth of correlations during the waiting time, $\xi_{TRM}$, (observed in both numerical studies and experiment), we observe both growth of $\xi_{TRM}$ in the spin glass phase and then a rapid reduction very close to $T_g$. We interpret this reduction in $\xi_{TRM}$, for all waiting times, as being governed by the critical correlation length scale $\xi_{crit}=a(TT_c)^{\nu}$.
 [9] arXiv:2003.11600 [pdf, other]

Title: Birefringent Graphene Oxide Liquid Crystals in Microchannels for Optical SwitchComments: 5 pages, 4 figuresJournalref: ACS Applied Nano Materials, Articles ASAP (Letter), February 24, 2020Subjects: Soft Condensed Matter (condmat.soft); Applied Physics (physics.appph); Optics (physics.optics)
We propose a mechanicalhydrodynamical experimental setup in which the microfluidic motion manipulates the optical birefringence of levitated graphene oxide liquid crystal. The birefringence of the sample is changed by flowing graphene oxide liquid crystal in the microchannel. By measuring the ordinary and extraordinary refractive indices at five flow rates, one can determine the value of the birefringence of the samples, precisely. Our results demonstrate that, by adjusting the concentration and flow rate of dispersion of the graphene oxide nano flakes, the induced birefringence can be controlled. It is also shown that this approach can be used as an optical switch.
 [10] arXiv:2003.11601 [pdf, other]

Title: Dualism of the 4f electrons and hightemperature antiferromagnetism of the heavyfermion compound YbCoC$_{2}$Authors: D. A. Salamatin, N. Martin, V. A. Sidorov, N. M. Chtchelkatchev, M. V. Magnitskaya, A. E. Petrova, I. P. Zibrov, L. N. Fomicheva, Jing Guo, Cheng Huang, Liling Sun, A. V. TsvyashchenkoComments: 25 pages, 8 figures, includes supplementJournalref: Physical Review B 101, 100406(R) (2020)Subjects: Strongly Correlated Electrons (condmat.strel); Materials Science (condmat.mtrlsci)
We report on the first study of the noncentrosymmetric ternary carbide YbCoC$_{2}$. Our magnetization, specific heat, resistivity and neutron diffraction measurements consistently show that the system behaves as a heavyfermion compound, displaying an amplitudemodulated magnetic structure below the N\'eel temperature reaching $T_{N}$ = 33 K under pressure. Such a large value, being the highest among the Ybbased systems, is explained in the light of our ab initio calculations, which show that the 4f electronic states of Yb have a dual nature  i.e., due to their strong hybridization with the 3d states of Co, 4f states expose both localized and itinerant properties.
 [11] arXiv:2003.11610 [pdf, other]

Title: Detecting chiral pairing and topological superfluidity using circular dichroismComments: 7 pages, 3 figuresSubjects: Quantum Gases (condmat.quantgas); Superconductivity (condmat.suprcon)
Realising and probing topological superfluids is a key goal for fundamental science, with exciting technological promises. Here, we show that chiral px + ipy pairing in a twodimensional topological superfluid can be detected through circular dichroism, namely, as a difference in the excitation rates induced by a clockwise and counterclockwise circular drive. For weak pairing, this difference is to a very good approximation determined by the Chern number of the superfluid, whereas there is a nontopological contribution scaling as the superfluid gap squared that becomes significant for stronger pairing. This gives rise to a competition between the experimentally driven goal to maximise the critical temperature of the superfluid, and observing a signal given by the underlying topology. Using a combination of strong coupling Eliashberg and BerezinskiiKosterlitzThouless theory, we analyse this tension for an atomic BoseFermi gas, which represents a promising platform for realising a chiral superfluid. We identify a wide range of system parameters where both the critical temperature is high and the topological contribution to the dichroic signal is dominant.
 [12] arXiv:2003.11621 [pdf, other]

Title: How Circular Dichroism in time and angleresolved photoemission can be used to spectroscopically detect transient topological states in grapheneAuthors: Michael Schüler, Umberto De Giovannini, Hannes Hübener, Angel Rubio, Michael A. Sentef, Thomas P. Devereaux, Philipp WernerComments: 16 pages, 8 figuresSubjects: Materials Science (condmat.mtrlsci); Strongly Correlated Electrons (condmat.strel)
Pumping graphene with circularly polarized light is the archetype of lighttailoring topological bands. Realizing the induced FloquetChern insulator state and tracing clear experimental manifestions has been a challenge, and it has become clear that scattering effects play a crucial role. We tackle this gap between theory and experiment by employing microscopic quantum kinetic calculations including realistic electronelectron and electronphonon scattering. Our theory provides a direct link to the buildup of the FloquetChern insulator state in lightdriven graphene and its detection in time and angleresolved photoemission spectroscopy (ARPES). This allows us to study the stability of the Floquet features due to dephasing and thermalization effects. We also discuss the ultrafast Hall response in the laserheated state. Furthermore, the induced pseudospin texture and the associated Berry curvature gives rise to momentumdependent orbital magnetization, which is reflected in circular dichroism in ARPES (CDARPES). Combining our nonequilibrium calculations with an accurate onestep theory of photoemission allows us to establish a direct link between the buildup of the topological state and the dichroic pumpprobe photoemission signal. The characteristic features in CDARPES are further corroborated to be stable against heating and dephasing effects. Thus, tracing circular dichroism in timeresolve photoemission provides new insights into transient topological properties.
 [13] arXiv:2003.11629 [pdf, other]

Title: Predicting plasticity in disordered solids from structural indicatorsAuthors: D. Richard, M. Ozawa, S. Patinet, E. Stanifer, B. Shang, S.A. Ridout, B. Xu, G. Zhang, P.K. Morse, J.L. Barrat, L. Berthier, M.L. Falk, P. Guan, A.J. Liu, K. Martens, S. Sastry, D. Vandembroucq, E. Lerner, M.L. ManningSubjects: Soft Condensed Matter (condmat.soft)
Amorphous solids lack longrange order. Therefore identifying structural defects  akin to dislocations in crystalline solids  that carry plastic flow in these systems remains a daunting challenge. By comparing many different structural indicators in computational models of glasses, under a variety of conditions we carefully assess which of these indicators are able to robustly identify the structural defects responsible for plastic flow in amorphous solids. We further demonstrate that the density of defects changes as a function of material preparation and strain in a manner that is highly correlated with the macroscopic material response. Our work represents an important step towards predicting how and when an amorphous solid will fail from its microscopic structure.
 [14] arXiv:2003.11633 [pdf]

Title: Universal Gelation of Metal Oxide Nanocrystals via Depletion AttractionsAuthors: Camila A. Saez Cabezas, Zachary M. Sherman, Michael P. Howard, Manuel N. Dominguez, Shin Hum Cho, Gary K. Ong, Allison Green, Thomas M. Truskett, Delia J. MillironSubjects: Soft Condensed Matter (condmat.soft)
Nanocrystal gelation provides a powerful framework to translate nanoscale properties into bulk materials and to engineer emergent properties through the assembled microstructure. However, many established gelation strategies rely on chemical reactions and specific interactions, e.g., stabilizing ligands or ions on the surface of the nanocrystals, and are therefore not easily transferrable. Here, we report a general gelation strategy via nonspecific and purely entropic depletion attractions applied to three types of metal oxide nanocrystals. The gelation thresholds of two compositionally distinct spherical nanocrystals agree quantitatively, demonstrating the adaptability of the approach for different chemistries. Consistent with theoretical phase behavior predictions, nanocrystal cubes form gels at a lower polymer concentration than nanocrystal spheres, allowing shape to serve as a handle to control gelation. These results suggest that the fundamental underpinnings of depletiondriven assembly, traditionally associated with larger colloidal particles, are also applicable at the nanoscale.
 [15] arXiv:2003.11649 [pdf, other]

Title: Nonreciprocity of spin waves in noncollinear magnets due to the DzyaloshinskiiMoriya interactionComments: 12 figuresSubjects: Mesoscale and Nanoscale Physics (condmat.meshall)
Broken inversion symmetry in combination with the spinorbit interaction generates a finite DzyaloshinskiiMoriya interaction (DMI), which can induce noncollinear spin textures of chiral nature. The DMI is characterized by an interaction vector whose magnitude, direction and symmetries are crucial to determine the stability of various spin textures, such as skyrmions and spin spirals. The DMI can be measured from the nonreciprocity of spin waves in ferromagnets, which can be probed via inelastic scattering experiments. In a ferromagnet, the DMI can modify the spinwave dispersion, moving its minimum away from the $\Gamma$ point. Spin waves propagating with opposite wavevectors are then characterized by different group velocities, energies and lifetimes, defining their nonreciprocity. Here, we address the case of complex spin textures, where the manifestation of DMIinduced chiral asymmetries remains to be explored. We discuss such nonreciprocal effects and propose ways of accessing the magnitude and direction of the DMI vectors in the context of spinpolarized or spinresolved inelastic scattering experiments. We show that only when a periodic magnetic system has finite net magnetization, that is, when the vector sum of all magnetic moments is nonzero, can it present a total nonreciprocal spinwave spectrum. However, even zeronetmagnetization systems, such as collinear antiferromagnets and cycloidal spin spirals, can have spinwave modes that are individually nonreciprocal, while the total spectrum remains reciprocal.
 [16] arXiv:2003.11659 [pdf, other]

Title: HartreeFockBogoliubov theory of trapped onedimensional imbalanced Fermi systemsComments: 11 pages, 3 figuresSubjects: Quantum Gases (condmat.quantgas); Strongly Correlated Electrons (condmat.strel)
Ground state HartreeFockBogoliubov (HFB) theory is applied to imbalanced spin1/2 onedimensional Fermi systems that are spatially confined by either a harmonic or a hardwall trapping potential. It has been hoped that such systems, which can be realized using ultracold atomic gases, would exhibit the longsoughtafter FuldeFerrellLarkinOvchinnikov (FFLO) superfluid phase. The HFB formalism generalizes the standard Bogoliubov quasiparticle transformation, by allowing for Cooper pairing to exist between all possible singleparticle states, and accounts for the effects of the inhomogeneous trapping potential as well as the meanfield Hartree potential. This provides an unbiased framework to describe inhomgenous densities and pairing correlations in the FFLO state of a confined 1D gas. In a harmonic trap, numerical minimization of the HFB ground state energy yields a spatially oscillating order parameter reminiscent of the FFLO state. However, we find that this state has almost no imprint in the local fermion densities (consistent with experiments that found no evidence of the FFLO phase). In contrast, for a hardwall geometry, we find a strong signature of the spatial oscillations of the FFLO pairing amplitude reflected in the local in situ densities. In the hard wall case, the excess spins are strongly localized near regions where there is a node in the pairing amplitude, creating an unmistakeable crystalline modulation of the density.
 [17] arXiv:2003.11669 [pdf, other]

Title: Measuring total density correlations in a FermiHubbard gas via bilayer microscopyComments: 8 pages, 8 figuresSubjects: Quantum Gases (condmat.quantgas)
We report on the single atom and single siteresolved detection of the total density in a cold atom realization of the 2D FermiHubbard model. Fluorescence imaging of doublons is achieved by splitting each lattice site into a double well, thereby separating atom pairs. Full density readout yields a direct measurement of the equation of state, including direct thermometry via the fluctuationdissipation theorem. Siteresolved density correlations reveal the Pauli hole at low filling, and strong doublonhole correlations near half filling. These are shown to account for the difference between local and nonlocal density fluctuations in the Mott insulator. Our technique enables the study of atomresolved charge transport in the FermiHubbard model, the siteresolved observation of molecules, and the creation of bilayer FermiHubbard systems.
 [18] arXiv:2003.11678 [pdf, other]

Title: Magneticfieldinduced FMAFM metamagnetic transition and strong negative magnetoresistance in Mn$_{1/4}$NbS$_2$ under pressureAuthors: S. Polesya, S. Mankovsky, P. G. Naumov, M. A. ElGhazali, W. Schnelle, S. Medvedev, S. Mangelsen, W. Bensch, H. EbertSubjects: Materials Science (condmat.mtrlsci)
Transition metal dichalcogenides (TMDC) stand out with their high chemical stability and the possibility to incorporate a wide range of magnetic species between the layers. The behavior of conduction electrons in such materials intercalated by 3delements is closely related to their magnetic properties and can be sensitively controlled by external magnetic fields. Here, we study the magnetotransport properties of NbS$_2$ intercalated with Mn, Mn$_{1/4}$NbS$_2$, demonstrating a complex behavior of the magnetoresistance and of the ordinary and anomalous Hall resistivities. Application of pressure as tuning parameter leads to the drastic changes of the magnetotransport properties of Mn$_{1/4}$NbS$_2$ exhibiting large negative magnetoresistance up to $65 \%$ at 7.1 GPa. Firstprinciples electronic structure calculations indicates pressureinduced transition from ferromagnetic to antiferromagnetic state. Theoretical calculations accounting for the finite temperature magnetic properties of Mn$_{1/4}$NbS$_2$ suggest a fieldinduced metamagnetic ferromagneticantiferromagnetic transition as an origin of the large negative magentoresistance. These results inspire the development of materials for spintronic applications based on intercalated TMDC with a well controllable metamagnetic transition.
 [19] arXiv:2003.11680 [pdf, other]

Title: Phase transition for parameter learning of Hidden Markov ModelsComments: 9 pages, 9 figuresSubjects: Statistical Mechanics (condmat.statmech); Biological Physics (physics.bioph); Computational Physics (physics.compph); Data Analysis, Statistics and Probability (physics.dataan)
We study a phase transition in parameter learning of Hidden Markov Models (HMMs). We do this by generating sequences of observed symbols from given discrete HMMs with uniformly distributed transition probabilities and a noise level encoded in the output probabilities. By using the BaumWelch (BW) algorithm, an ExpectationMaximization algorithm from the field of Machine Learning, we then try to estimate the parameters of each investigated realization of an HMM. We study HMMs with n=4, 8 and 16 states. By changing the amount of accessible learning data and the noise level, we observe a phasetransitionlike change in the performance of the learning algorithm. For bigger HMMs and more learning data, the learning behavior improves tremendously below a certain threshold in the noise strength. For a noise level above the threshold, learning is not possible. Furthermore, we use an overlap parameter applied to the results of a maximumaposteriori (Viterbi) algorithm to investigate the accuracy of the hidden state estimation around the phase transition.
 [20] arXiv:2003.11697 [pdf, other]

Title: Tsquare resistivity without Umklapp scattering in dilute metallic Bi$_2$O$_2$SeAuthors: Jialu Wang, Jing Wu, Tao Wang, Zhuokai Xu, Jifeng Wu, Wanghua Hu, Zhi Ren, Shi Liu, Kamran Behnia, Xiao LinComments: 7 pages, 4 figuresSubjects: Strongly Correlated Electrons (condmat.strel)
The electrical resistivity of Fermi liquids (FLs) displays a quadratic temperature ($T$) dependence because of electronelectron (ee) scattering. For such collisions to decay the charge current, there are two known mechanisms: interband scattering (identified by Baber) and Umklapp events. However, dilute metallic strontium titanate (STO) was found to display $T^2$ resistivity in absence of either of these two mechanisms. The presence of soft phonons and their possible role as scattering centers raised the suspicion that $T$square resistivity in STO is not due to ee scattering. Here, we present the case of Bi$_2$O$_2$Se, a layered semiconductor with hard phonons, which becomes a dilute metal with a small singlecomponent Fermi surface upon doping. It displays $T$square resistivity well below the degeneracy temperature where neither Umklapp nor interband scattering is conceivable. We observe a universal scaling between the prefactor of $T^2$ resistivity and the Fermi energy, which is an extension of the KadowakiWoods plot to dilute metals. Our results imply the absence of a satisfactory theoretical basis for the ubiquity of ee driven $T$square resistivity in Fermi liquids.
 [21] arXiv:2003.11710 [pdf, other]

Title: Fermi polaron revisited: polaronmolecule transition and coexistenceAuthors: Xiaoling CuiComments: 5 pages, 4 figuresSubjects: Quantum Gases (condmat.quantgas)
We revisit the polaronmolecule transition in ultracold Fermi gases using the wellestablished variational approach. It is found that the molecule is in fact an asymptotic limit of a finitemomentum polaron in the strong coupling regime, which can be continuously connected to the weak coupling polaronic state in the same momentum sector. The polaronmolecule transition can therefore be reinterpreted as a firstorder transition between Fermi polarons with different momenta. Within certain interaction window near their transition, both states appear as local minima in the dispersion curve, indicating they can coexist in a realistic system. We have further confirmed the polaronmolecule coexistence in the presence of a finite impurity concentration and at low temperature, which well explains the recent experimental observations of smooth polaronmolecule transition in a threedimensional ultracold Fermi gas. Our results have provided an unambiguous physical picture for the competition and conversion between polaron and molecule, and also shed light on Fermi polaron properties in low dimensions.
 [22] arXiv:2003.11731 [pdf]

Title: Giant linear nonreciprocal charge transport in onedimensional channels with a magnetic proximity effectSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Materials Science (condmat.mtrlsci)
In noncentrosymmetric conducting channels, the electrical resistance $R$ differs when the current flows in forward ($R^+$) and backward ($R^$) directions under an external magnetic field $B$, which results from breaking of both the spatial inversion symmetry (SIS) and time reversal symmetry (TRS). Thus far, this nonreciprocal charge transport has been observed only in the nonlinear transport regime by using second harmonic measurements, where the resistance difference $R^+  R^$ is proportional to both the current intensity $I$ and magnetic field $B$, and these $R^+  R^$ values were minuscule, ~0.01$\%$ of the total resistance. Here, we report a new nonreciprocal charge transport phenomenon observed in the linear response regime, which is independent of $I$, in chiral onedimensional (1D) edge channels of an InAs thin film interfaced with a ferromagnetic semiconductor (FMS) (Ga,Fe)Sb layer.By switching the $B$ direction, the resistance change between $\pm$ 10 T of the 1D channels is as large as 27$\%$ and is clearly detected by DC transport measurements. Our theoretical analysis using Boltzmann's equation suggests that the relativistic spinorbit interaction (SOI) in the 1D channels and the spindependent scattering at the InAs/(Ga,Fe)Sb interface are the origins of this phenomenon. These findings suggest that utilizing the magnetic proximity effect (MPE) is a revolutionary way to study nonreciprocal electrical transport, which is directly related to fundamental issues in condensed matter physics such as symmetries.
 [23] arXiv:2003.11742 [pdf, ps, other]

Title: Possible occurrence of superconductivity by the $π$flux Dirac string formation due to spintwisting itinerant motion of electronsAuthors: Hiroyasu KoizumiSubjects: Superconductivity (condmat.suprcon)
We show that the Rashba spinorbit interaction causes spintwisting itinerant motion of electrons in metals and realizes the quantized cyclotron motion of conduction electrons without an external magnetic field. From the view point of the Berry connection, the cause of this {quantized} motion is the appearance of a nontrivial Berry connection ${\bf A}^{\rm fic}={\hbar \over {2e}}\nabla \chi$ ($\chi$ is an angular variable with period $2\pi$ that generates $\pi$ flux (in the units of $\hbar=1, e=1,c=1$) inside the nodal singularities of the wave function (a "Dirac string") along the centers of spintwisting.
Since it has been shown in our previous work[Ref.1]that the collective mode of $\nabla \chi$ is stabilized by the electronpairing and generates supercurrent, the $\pi$flux Dirac string created by the spintwisting itinerant motion will be stabilized by the electronpairing and produce supercurrent.  [24] arXiv:2003.11752 [pdf, other]

Title: Topological superconductor from superconducting topological surface states and faulttolerant quantum computingComments: 6 pages, 5 figuresSubjects: Superconductivity (condmat.suprcon); Quantum Physics (quantph)
The chiral $p$wave superconductor/superfluid in two dimensions (2D) is the simplest and most robust system for topological quantum computation . Candidates for such topological superconductors/superfluids in nature are very rare. A widely believed chiral $p$wave superfluid is the MooreRead state in the $\nu=\frac{5}2$ fractional quantum Hall effect, although experimental evidence are not yet conclusive. Experimental realizations of chiral $p$wave superconductors using quantum anomalous Hall insulatorsuperconductor hybrid structures have been controversial. Here we report a new mechanism for realizing 2D chiral $p$wave superconductors on the surface of 3D $s$wave superconductors that have a topological band structure and support superconducting topological surface states (SCTSS), such as the ironbased superconductor Fe(Te,Se). We find that tunneling and pairing between the SCTSS on the top and bottom surfaces in a thin film or between two opposing surfaces of two such superconductors can produce an emergent 2D timereversal symmetry breaking chiral topological superconductor. The topologically protected anyonic vortices with Majorana zero modes as well as the chiral Majorana fermion edge modes can be used as a platform for more advantageous nonabelian braiding operations. We propose a novel device for the CNOT gate with six chiral Majorana fermion edge modes, which paves the way for faulttolerant universal quantum computing.
 [25] arXiv:2003.11762 [pdf]

Title: Moire supercells through SrTiO$_3$ nanolayer relaxationAuthors: Max Burian, Bill Francesco Pedrini, Nazaret Ortiz Hernandez, Hiroki Ueda, C. A. F. Vaz, Milan Radovic, Urs StaubComments: 21 pages, 4 figuresSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Strongly Correlated Electrons (condmat.strel)
The interface of complex oxide heterostructures sets the stage for various electronic and magnetic phenomena. Many of these collective effects originate from the precise structural arrangement at the interface that in turn governs local spin and charge interactions. Currently, interfacial straining, so the naturally evolving compressive or tensile strain by mismatch of the neighboring lattices, is the most common route towards engineering collective material properties  yet, significant progress might require exploration of entirely new approaches towards interface correlations. In this work, we turn the page by looking at the interface of a perfectly relaxed, unstrained heterostructure, where we identify a highly ordered Moire lattice at an inherently disordered SrTiO$_3$ (STO)  LSAT interface. Using highresolution reciprocal space mapping via synchrotron based XRay diffraction, we find longranged ordered supercells of 106/107 unit cells of STO/LSAT, caused by lattice relaxation through hightemperature annealing. Model calculations confirm the experimentally observed scattering phenomena, showing that crossinterfacial bonding is locally different at the Moireoverlap points. Notably, the presence of such superordered structures in the family of 2D electron gas systems sets the ideal conditions for Moiremotif tuned plasmonic responses and ferroelectric supercrystallinity and opens up the possibility to novel interface functionalities in these simple perovskites.
 [26] arXiv:2003.11765 [pdf, ps, other]

Title: Fingerprints of spincurrent physics on magnetoelectric response in the spin$1/2$ magnet Ba$_2$CuGe$_2$O$_7$Comments: 15 pages, 8 figuresSubjects: Strongly Correlated Electrons (condmat.strel); Materials Science (condmat.mtrlsci)
The singlesite anisotropy vanishes for the spin1/2 as a consequence of Kramers degeneracy. We argue that similar property holds for the magnetically induced electric polarization P, which should depend only on the relative orientation of spins in the bonds but not on the direction of each individual spin. Thus, for insulating multiferroic compounds, P can be decomposed in terms of pairwise isotropic, antisymmetric, and anisotropic contributions, which can be rigorously derived in the framework of the superexchange (SE) theory, in an analogy with the spin Hamiltonian. The SE theory also allows us to identify the microscopic mechanism, which stands behind each contribution. The most controversial and intriguing one is antisymmetric or spincurrent mechanism. In this work, we propose that the disputed magnetoelectric (ME) properties of Ba2CuGe2O7 can be explained solely by the spincurrent mechanism, while other contributions are either small or forbidden by symmetry. First we explicitly show how the cycloidal spin order induces the experimentally observed P in the direction perpendicular to the xy plane, which can be naturally explained by the spincurrent mechanism operating in the outofplane bonds. Then, we unveil previously overlooked ME effect, where the application of the magnetic field perpendicular to the plane not only causes the incommensuratecommensurate transition, but also flips P into the plane due to the spincurrent mechanism operating in the neighboring bonds within this plane. In both cases, the magnitude and direction of P can be controlled by rotating the spin pattern in the xy plane. Our analysis is based on a realistic spin model, which was rigorously derived from the firstprinciples calculations and supplemented with the new algorithm for the construction of localized Wannier functions obeying the crystallographic symmetry of Ba2CuGe2O7.
 [27] arXiv:2003.11767 [pdf, other]

Title: Study of classical and quantum phase transitions on nonEuclidean geometries in higher dimensionsComments: accepted in Acta Physica Slovaca (a review based on Michal Daniska's PhD thesis)Subjects: Statistical Mechanics (condmat.statmech)
The investigation of the behavior of both classical and quantum systems on nonEuclidean surfaces near the phase transition point represents an interesting research area of modern physics. In the case of classical spin systems, a generalization of the Corner Transfer Matrix Renormalization Group algorithm has been developed and successfully applied to spin models on infinitely many regular hyperbolic lattices. In this work, we extend these studies to specific types of lattices. It is important to say that no suitable algorithms for numerical analysis of groundstates of quantum systems in similar conditions have been implemented yet. In this work, we offer a particular solution by proposing a variational numerical algorithm Tensor Product Variational Formulation, which assumes a quantum groundstate written in the form of a lowdimensional uniform tensor product state. We apply the Tensor Product Variational Formulation to three typical quantum models on a variety of regular hyperbolic lattices. The main outcomes are the following: (1) We propose an algorithm for calculation and classification of the thermodynamic properties of the Ising model on triangulartiled hyperbolic lattices. In addition, we investigate the origin of the meanfield universality on a series of weakly curved lattices. (2) We develop the Tensor Product Variational Formulation algorithm for the numerical analysis of the groundstate of the quantum systems on the hyperbolic lattices. (3) We study quantum phase transition phenomena for the three selected spin models on various types of the hyperbolic lattices including the Bethe lattice.
 [28] arXiv:2003.11800 [pdf]

Title: Distinguishing strain, charge and molecular orbital induced effects on the electronic structure: graphene/ammonia systemSubjects: Materials Science (condmat.mtrlsci)
Molecular adsorption at the surface of a 2D material poses numerous questions regarding the modification to the band structure and interfacial states, which of course deserve full attention. In line with this, firstprinciple density functional theory is employed on the graphene/ammonia system. We identify the effects on the band structure due to strain, charge transfer and presence of molecular orbitals (MOs) of NH3 for six adsorption configurations. The induced strain upon ammoniaadsorption opens the bandgap (Eg) of graphene due to the breaking of translational symmetry and shifts the equilibrium Fermi energy (EF). The Eg and EF values and charge density distribution are dependent on the adsorption configuration, where the MO structure of NH3 plays a crucial role. The presence of MOs of N or H originated pushes the unoccupied states of graphene towards EF. NH3 forms an interfacial occupied state originating from N2p below the EF within 1.6  2.2 eV for all configurations. These findings enhance the fundamental understanding of the graphene/NH3 system.
 [29] arXiv:2003.11804 [pdf, other]

Title: Active Learning Approach to Optimization of Experimental ControlSubjects: Quantum Gases (condmat.quantgas); Machine Learning (cs.LG); Quantum Physics (quantph)
In this work we present a general machine learning based scheme to optimize experimental control. The method utilizes the neural network to learn the relation between the control parameters and the control goal, with which the optimal control parameters can be obtained. The main challenge of this approach is that the labeled data obtained from experiments are not abundant. The central idea of our scheme is to use the active learning to overcome this difficulty. As a demonstration example, we apply our method to control evaporative cooling experiments in cold atoms. We have first tested our method with simulated data and then applied our method to real experiments. We demonstrate that our method can successfully reach the best performance within hundreds of experimental runs. Our method does not require knowledge of the experimental system as a prior and is universal for experimental control in different systems.
 [30] arXiv:2003.11805 [pdf, other]

Title: Chiral Domain Wall Injector Driven by Spinorbit TorquesAuthors: T. Phuong Dao, Marvin Müller, Zhaochu Luo, Manuel Baumgartner, Aleš Hrabec, Laura J. Heyderman, Pietro GambardellaJournalref: Nano Lett. 2019, 19, 9, 59305937Subjects: Mesoscale and Nanoscale Physics (condmat.meshall); Materials Science (condmat.mtrlsci)
Memory and logic devices that encode information in magnetic domains rely on the controlled injection of domain walls to reach their full potential. In this work, we exploit the chiral coupling induced by the DzyaloshinskiiMoriya interaction between inplane and outofplane magnetized regions of a Pt/Co/AlO\textsubscript{x} trilayer in combination with currentdriven spinorbit torques to control the injection of domain walls into magnetic conduits. We demonstrate that the currentinduced domain nucleation is strongly inhibited for magnetic configurations stabilized by the chiral coupling and promoted for those that have the opposite chirality. These configurations allow for efficient domain wall injection using current densities of the order of $4\times$\SI{e11}{A m^{2}}, which are lower than those used in other injection schemes. Furthermore, by setting the orientation of the inplane magnetization using an external field, we demonstrate the use of a chiral domain wall injector to create a controlled sequence of alternating domains in a racetrack structure driven by a steady stream of unipolar current pulses.
 [31] arXiv:2003.11809 [pdf, other]

Title: Theory of absorption lineshape in monolayers of transition metal dichalcogenidesComments: to be published in Physical Review BSubjects: Mesoscale and Nanoscale Physics (condmat.meshall)
The linear absorption spectra in monolayers of transition metal dichalcogenides show pronounced signatures of the exceptionally strong excitonphonon interaction in these materials. To account for both exciton and phonon physics in such optical signals, we compare different theoretical methods to calculate the absorption spectra using the example of $\mathrm{MoSe_2}$. In this paper, we derive the equations of motion for the polarization either using a correlation expansion up to 4th Born approximation or a time convolutionless master equation. We show that the Born approximation might become problematic when not treated in high enough order, especially at high temperatures. In contrast, the time convolutionless formulation gives surprisingly good results despite its simplicity when compared to higherorder corrrelation expansion and therefore provides a powerful tool to calculate the lineshape of linear absorption spectra in the very popular monolayer materials.
 [32] arXiv:2003.11825 [pdf, other]

Title: Multiparticle collision dynamics for fluid interfaces with nearcontact interactionsSubjects: Soft Condensed Matter (condmat.soft)
We present an extension of the multiparticle collision dynamics method for flows with complex interfaces, including supramolecular nearcontact interactions mimicking the effect of surfactants. The new method is demonstrated for the case of (i) short range repulsion of droplets in close contact, (ii) arrested phase separation and (iii) different pattern formation during spinodal decomposition of binary mixtures.
 [33] arXiv:2003.11829 [pdf, other]

Title: Experimental realization of spintensor momentum coupling in ultracold Fermi gasesAuthors: Donghao Li, Lianghui Huang, Peng Peng, Guoqi Bian, Pengjun Wang, Zengming Meng, Liangchao Chen, Jing ZhangComments: 6 pages, 4 figuresSubjects: Quantum Gases (condmat.quantgas)
We experimentally realize the spintensor momentum coupling (STMC) using the three ground Zeeman states coupled by three Raman laser beams in ultracold atomic system of $^{40}$K Fermi atoms. This new type of STMC consists of two brightstate bands as a regular spinorbit coupled spin1/2 system and one darkstate middle band. Using radiofrequency spininjection spectroscopy, we investigate the energy band of STMC. It is demonstrated that the middle state is a dark state in the STMC system. The realized energy band of STMC may open the door for further exploring exotic quantum matters.
 [34] arXiv:2003.11833 [pdf, other]

Title: Quantum corrections to the classical field approximation for 1D quantum manybody systems in equilibriumComments: 16 pages, 6 figuresSubjects: Statistical Mechanics (condmat.statmech); Quantum Gases (condmat.quantgas)
We present a semiclassical treatment of one dimensional manybody quantum systems in equilibrium, where quantum corrections to the classical field approximation are systematically included by a renormalization of the classical field parameters. Our semiclassical approximation is reliable in the limit of weak interactions and high temperatures. As a specific example, we apply our method to the interacting Bose gas and study experimentally observable quantities, such as correlation functions of bosonic fields and the full counting statistics of the number of particles in an interval. Where possible, our method is checked against exact results derived from integrability, showing excellent agreement.
 [35] arXiv:2003.11841 [pdf]

Title: A QM/MD coupling method to model the ioninduced polarization of grapheneComments: 19 pages, 6 figuresSubjects: Materials Science (condmat.mtrlsci)
We report a new Quantum Mechanical/Molecular Dynamics (QM/MD) simulation loop to model the coupling between the electron and atom dynamics in solid/liquid interfacial systems. The method can describe simultaneously both the quantum mechanical surface polarizability emerging from the proximity to the electrolyte, and the electrolyte structure and dynamics. In the current set up Density Functional Tight Binding calculations for the electronic structure calculations of the surface are coupled with classical molecular dynamics to simulate the electrolyte solution. The reduced computational cost of the QM part makes the coupling with a classical simulation engine computationally feasible and allows simulation of large systems for hundreds of nanoseconds. We tested the method by simulating a noncharged graphene flake immersed in an NaCl electrolyte solution at varying concentrations. We found that ions preferentially remained in solution and only cations are mildly attracted to the surface of the graphene. This behaviour is found to originate from the relatively small adsorption energy compared to the value of the ion hydration energy and rules out any possible ions/surface charge transfer.
 [36] arXiv:2003.11847 [pdf, other]

Title: The ManyBody localization transition in the Hilbert spaceAuthors: Marco TarziaComments: 15 pages, 10 figuresSubjects: Statistical Mechanics (condmat.statmech); Disordered Systems and Neural Networks (condmat.disnn)
In this paper we propose a new perspective to analyze the manybody localization (MBL) transition when recast in terms of a singleparticle tightbinding model in the space of manybody configurations. We compute the distribution of tunneling rates between manybody states separated by an extensive number of spin flips at the lowest order in perturbation theory starting from the insulator, and determine the scaling of their typical amplitude with the number of accessible states in the Hilbert space. By using an analogy with the RosenzweigPorter random matrix ensemble, we propose an ergodicity breaking criterion for the MBL transition based on the Fermi Golden Rule. According to this criterion, in the MBL phase many resonances are formed at large distance from an infinite temperature initial state, but they are not enough for the quantum dynamics to decorrelate from it in a finite time. This implies that, differently from Anderson localized states, in the insulating phase manybody eigenstates are multifractal in the Hilbert space, as they occupy a large but subexponential part of the total volume, in agreement with recent numerical results, perturbative calculations, and intuitive arguments. Possible limitations and implications of our interpretation are discussed in the conclusions.
 [37] arXiv:2003.11849 [pdf]

Title: Electronphonon coupling and a resonantlike optical observation of a band inversion in topological crystalline insulator Pb$_{1x}$Sn$_x$SeAuthors: Mariusz Woźny, Wojciech Szuszkiewicz, Mateusz Dyksik, Marcin Motyka, Andrzej Szczerbakow, Witold Bardyszewski, Tomasz Story, Józef CebulskiComments: 12 pages, 5 figuresSubjects: Materials Science (condmat.mtrlsci)
The optical reflectivity of Pb$_{0.865}$Sn$_{0.135}$Se and Pb$_{0.75}$Sn$_{0.25}$Se solid solutions was measured in the THz spectral region energetically corresponding to bulk optical phonon excitations and in the temperature range from 40 K to 280 K. The analysis of Pb$_{0.75}$Sn$_{0.25}$Se data performed within the dynamic dielectric function formalism revealed a new effect due to the electronphonon coupling resulting in resonant changes of LO phonon frequency for energy gap equal to zero or to LO phonon energy. This effect is absent for Pb$_{0.865}$Sn$_{0.135}$Se that exhibits an open energy gap with trivial band ordering at all temperatures. These results show that reflectivity in the THz range constitute a versatile experimental method for precise determination of band inversion in narrowgap topological materials. For Pb$_{0.75}$Sn$_{0.25}$Se the transition from trivial insulator to topological crystalline insulator phase takes place at temperature T$_0$ = (172 $\pm$ 2) K.
 [38] arXiv:2003.11866 [pdf, other]

Title: Griffithslike phase close to the Mott transitionComments: 5 pages, 3 figuresSubjects: Strongly Correlated Electrons (condmat.strel); Materials Science (condmat.mtrlsci); Other Condensed Matter (condmat.other)
We explore the coexistence region in the vicinity of the Mott critical end point employing a coupled energyvolume spin$1/2$ Isinglike model. We analyze the case for the spinliquid candidate $\kappa$(BEDTTTF)$_2$Cu$_2$(CN)$_3$, where close to the Mott critical end point metallic puddles coexist with an insulating ferroelectric phase. Our results are fourfold: $i$) a universal divergentlike behavior of the Gr\"uneisen parameter upon crossing the spinodal line; $ii$) based on scaling arguments, we show that in the coexistence region, for $any$ system close to the critical point, the relaxation time is entropydependent; $iii$) we propose the electric Gr\"uneisen parameter $\Gamma_E$, which quantifies the electrocaloric effect; $iv$) we identify the metallic/insulating coexistence region as a Griffiths phase. Our findings suggest that $\Gamma_E$ governs the dielectric response close to the critical point and that a Griffithslike phase emerges in the coexistence region of any system.
 [39] arXiv:2003.11873 [pdf, other]

Title: Unveiling the Physics of the Mutual Interactions in ParamagnetsAuthors: Lucas Squillante, Isys F. Mello, Gabriel O. Gomes, A. C. Seridonio, R. E. LagosMonaco, H. Eugene Stanley, Mariano de SouzaComments: 21 pages, 8 figuresSubjects: Strongly Correlated Electrons (condmat.strel); Materials Science (condmat.mtrlsci); Other Condensed Matter (condmat.other); Statistical Mechanics (condmat.statmech)
In real paramagnets, there is always a subtle manybody contribution to the system's energy, which can be regarded as a small effective local magnetic field $B_{loc}$. Usually, it is neglected, since it is very small when compared with thermal fluctuations and/or external magnetic fields $B$. Nevertheless, as both the temperature $T \rightarrow$ 0K and $B \rightarrow$ 0T, such manybody contributions become ubiquitous. Here, employing the magnetic Gr\"uneisen parameter $\Gamma_{mag}$ and entropy arguments, we report on the pivotal role played by the mutual interactions in the regime of ultralow$T$ and vanishing $B$. Our key results are: $i$) absence of a genuine zerofield quantum phase transition due to the presence of $B_{loc}$; $ii$) connection between the canonical definition of temperature and $\Gamma_{mag}$; and $iii$) possibility of performing adiabatic magnetization by only manipulating the mutual interactions. Our findings unveil unprecedented aspects emerging from the mutual interactions.
 [40] arXiv:2003.11876 [pdf, other]

Title: Emergence of a nematic paramagnet via quantum orderbydisorder and pseudoGoldstone modes in Kitaev magnetsComments: 14 pages, 9 figureSubjects: Strongly Correlated Electrons (condmat.strel)
The appearance of nontrivial phases in Kitaev materials exposed to an external magnetic field has recently been a subject of intensive studies. Here, we elucidate the relation between the fieldinduced ground states of the classical and quantum spin models proposed for such materials, by using the infinite density matrix renormalization group (iDMRG) and the linear spin wave theory (LSWT). We consider the $K \Gamma \Gamma'$ model, where $\Gamma$ and $\Gamma'$ are offdiagonal spin exchanges on top of the dominant Kitaev interaction $K$. We show that a nematic paramagnet, which breaks the latticerotational symmetry, emerges in the quantum model. This phenomenon can be understood as the effect of quantum orderbydisorder in the frustrated ferromagnet discovered in the corresponding classical model. In addition, various classical ordering patterns with large unit cells are replaced by the nematic paramagnet in the quantum model. We compute the dynamical spin structure factors using a matrix operator based time evolution and compare them with the predictions from LSWT. We point out the existence of a pseudoGoldstone mode, which results from the lifting of a continuous degeneracy via quantum fluctuations. We also discuss these results in the light of inelastic neutron scattering experiments.
 [41] arXiv:2003.11879 [pdf, other]

Title: Pressure and electric field dependence of quasicrystalline electronic states in 30$^{\circ}$ twisted bilayer grapheneComments: 7 pages, 8 figures, 1 tableSubjects: Materials Science (condmat.mtrlsci); Mesoscale and Nanoscale Physics (condmat.meshall)
30$^{\circ}$ twisted bilayer graphene demonstrates the quasicrystalline electronic states with 12fold symmetry. These states are however far away from the Fermi level, which makes conventional Dirac fermion behavior dominating the low energy spectrum in this system. By using tightbinding approximation, we study the effect of external pressure and electric field on the quasicrystalline electronic states. Our results show that by applying the pressure perpendicular to graphene plane one can push the quasicrystalline electronic states towards the Fermi level. Then, the electron or hole doping of the order of $\sim$ $4\times10^{14}$ $cm^{2}$ is sufficient for the coincidence of the Fermi level with these quasicrystalline states. Moreover, our study indicates that applying the electric field perpendicular to the graphene plane can destroy the 12fold symmetry of these states and break the energy degeneracy of the 12wave states, and it is easier to reach this in the conduction band than in the valence band. Importantly, the application of the pressure can recover the 12fold symmetry of these states to some extent against the electric field. We propose a hybridization picture which can explain all these phenomena.
 [42] arXiv:2003.11898 [pdf, other]

Title: A simple approach to bulk bioinspired tough ceramicsAuthors: Hassan Saad, Kaoutar Radi, Thierry Douillard, David Jauffres, Christophe L. Martin, Sylvain Meille, Sylvain DevilleComments: 7 pages, 4 figuresSubjects: Materials Science (condmat.mtrlsci); Applied Physics (physics.appph)
The development of damageresistant structural materials that can withstand harsh environments is a major issue in materials science and engineering. Bioinspired brickandmortar designs have recently demonstrated a range of interesting mechanical properties in proofofconcept studies. However, reproducibility and scalability issues associated with the actual processing routes have impeded further developments and industrialization of such materials. Here we demonstrate a simple approach based on uniaxial pressing and field assisted sintering of commercially available raw materials to process bioinspired ceramic/ceramic composites of larger thickness than previous approaches, with a sample thickness up to 1 cm. The ceramic composite retains the strength typical of dense alumina ($430~\pm 30MPa$) while keeping the excellent damage resistance demonstrated previously at the millimeter scale with a crack initiation toughness of $6.6MPa.m^{1/2}$ and fracture toughness up to $17.6 MPa.m^{1/2}$. These results validate the potential of these allceramic composites, previously demonstrated at lab scale only, and could enable their optimization, scaleup, and industrialization.
 [43] arXiv:2003.11905 [pdf]

Title: Fermi liquid behavior and colossal magnetoresistance in layered MoOCl2Authors: Zhi Wang, Meng Huang, Jianzhou Zhao, Cong Chen, Haoliang Huang, Xiangqi Wang, Ping Liu, Jianlin Wang, Junxiang Xiang, Chao Feng, Zengming Zhang, Xudong Cui, Yalin Lu, Shengyuan A. Yang, Bin XiangSubjects: Materials Science (condmat.mtrlsci)
A characteristic of a Fermi liquid is the T^2 dependence of its resistivity, sometimes referred to as the Baber law. However, for most metals, this behavior is only restricted to very low temperatures, usually below 20 K. Here, we experimentally demonstrate that for the singlecrystal van der Waals layered material MoOCl2, the Baber law holds in a wide temperature range up to ~120 K, indicating that the electronelectron scattering plays a dominant role in this material. Combining with the specific heat measurement, we find that the modified KadowakiWoods ratio of the material agrees well with many other strongly correlated metals. Furthermore, in the magnetotransport measurement, a colossal magnetoresistance is observed, which reaches ~350% at 9 T and displays no sign of saturation. With the help of firstprinciples calculations, we attribute this behavior to the presence of open orbits on the Fermi surface. We also suggest that the dominance of electronelectron scattering is related to an incipient charge density wave state of the material. Our results establish MoOCl2 as a strongly correlated metal and shed light on the underlying physical mechanism, which may open a new path for exploring the effects of electronelectron interaction in van der Waals layered structures.
 [44] arXiv:2003.11935 [pdf, ps, other]

Title: Full counting statistics and fluctuationdissipation relation for periodically driven systemsComments: 11 pages, 7 figuresSubjects: Statistical Mechanics (condmat.statmech); Mesoscale and Nanoscale Physics (condmat.meshall)
We derive the fluctuation theorem for a stochastic and periodically driven system coupled to two reservoirs with the aid of a master equation. We write down the cumulant generating functions for both the current and entropy production in closed compact forms so as to treat the adiabatic and nonadiabatic contributions systematically. We derive the fluctuation theorem by taking into account the property that the instantaneous currents flowing into the left and the right reservoir are not equal. It is found that the fluctuationdissipation relation derived from the fluctuation theorem involves an expansion with respect to the time derivative of the affinity in addition to the standard contribution.
 [45] arXiv:2003.11957 [pdf]

Title: Large Nernst Power Factor over a Broad Temperature Range in Polycrystalline Weyl Semimetal NbPAuthors: Chenguang Fu, Satya N. Guin, Sarah J. Watzman, Guowei Li, Enke Liu, Nitesh Kumar, Vicky Süß, Walter Schnelle, Gudrun Auffermann, Chandra Shekhar, Yan Sun, Johannes Gooth, Claudia FelserJournalref: Energy Environ. Sci. 11 (2018) 28132820Subjects: Materials Science (condmat.mtrlsci)
The discovery of topological materials has provided new opportunities to exploit advanced materials for heattoelectricity energy conversion as they share many common characteristics with thermoelectric materials. In this work, we report the magnetothermoelectric properties and Nernst effect of the topological Weyl semimetal NbP. We find that polycrystalline, bulk NbP shows a significantly larger Nernst thermopower than its conventional thermopower under magnetic field. As a result, a maximum Nernst power factor of ~ 35*104 Wm1K2 is achieved at 9 T and 136 K, which is 4 times higher than its conventional power factor and is also comparable to that of stateoftheart thermoelectrics. Moreover, the Nernst power factor maintains relatively large value over a broad temperature range. These results highlight that the enhancement of thermoelectric performance can be achieved in topological semimetals based on the Nernst effect and transverse transport.
 [46] arXiv:2003.11966 [pdf, other]

Title: Van der Waals materials for energyefficient spinorbit torque devicesComments: Comments are welcomeSubjects: Mesoscale and Nanoscale Physics (condmat.meshall); Materials Science (condmat.mtrlsci)
Spinorbit torques (SOTs), which rely on spin current generation from charge current in a nonmagnetic material, promise an energyefficient scheme for manipulating magnetization in magnetic devices. A critical topic for spintronic devices using SOTs is to enhance the charge to spin conversion efficiency. Besides, the currentinduced spin polarization is usually limited to inplane, whereas out of plane spin polarization could be favored for efficient perpendicular magnetization switching. Recent advances in utilizing two important classes of van der Waals materials$$topological insulators and transitionmetal dichalcogenides$$as spin source to generate SOT shed light on addressing these challenges. Topological insulators such as bismuth selenide have shown a giant SOT efficiency, which is larger than those from threedimensional heavy metals by at least one order of magnitude. Transitionmetal dichalcogenides such as tungsten telluride have shown a currentinduced out of plane spin polarization, which is allowed by the reduced symmetry. In this review, we use symmetry arguments to predict and analyze SOTs in van der Waal materialbased heterostructures. We summarize the recent progress of SOT studies based on topological insulators and transitionmetal dichalcogenides and show how these results are in line with the symmetry arguments. At last, we identify unsolved issues in the current studies and suggest three potential research directions in this field.
 [47] arXiv:2003.11968 [pdf, other]

Title: Efficient Calculation of Excitonic Effects in Solids Including Approximated Quasiparticle EnergiesSubjects: Materials Science (condmat.mtrlsci)
In this work we present a new procedure to compute optical spectra including excitonic effects and approximated quasiparticle corrections with reduced computational effort. The excitonic effects on optical spectra are included by solving the BetheSalpeter equation, considering quasiparticle eigenenergies and respective wavefunctions obtained within DFT1/2 method. The electronhole ladder diagrams are approximated by the screened exchange. To prove the capability of the procedure, we compare the calculated imaginary part of the dielectric functions of Si, Ge, GaAs, GaP, GaSb, InAs, InP, and InSb with experimental data. The energy position of the absorption peaks are correctly described. The good agreement with experimental results together with the very significant reduction of computational effort makes the procedure suitable on the investigation of optical spectra of more complex systems.
 [48] arXiv:2003.11977 [pdf, other]

Title: High frequency mechanical excitation of a silicon nanostring with piezoelectric aluminum nitride layersAuthors: A. Pitanti, T. Makkonen, M. F. Colombano, S. Zanotto, L. Vicarelli, A. Griol, D. NavarroUrrios, C. SotomayorTorres, A. Martinez, J. AhopeltoSubjects: Applied Physics (physics.appph); Mesoscale and Nanoscale Physics (condmat.meshall)
A strong trend for quantum based technologies and applications follows the avenue of combining different platforms to exploit their complementary technological and functional advantages. Micro and nanomechanical devices are particularly suitable for hybrid integration due to the easiness of fabrication at multiscales and their pervasive coupling with electrons and photons. Here, we report on a nanomechanical technological platform where a silicon chip is combined with an aluminum nitride layer. Exploiting the AlN piezoelectricity, Surface Acoustic Waves are injected in the Si layer where the material has been localy patterned and etched to form a suspended nanostring. Characterizing the nanostring vertical displacement induced by the SAW, we found an external excitation peak efficiency in excess of 500 pm/V at 1 GHz mechanical frequency. Exploiting the long term expertise in silicon photonic and electronic devices as well as the SAW robustness and versatility, our technological platform represents a strong candidate for hybrid quantum systems.
 [49] arXiv:2003.12024 [pdf, other]

Title: SubTHz momentum drag and violation of Matthiessen's rule in an ultraclean ferromagnetic SrRuO$_3$ metallic thin filmAuthors: Youcheng Wang, G. Bosse, H. P. Nair, N. J. Schreiber, J. P. Ruf, B. Cheng, C. Adamo, D. E. Shai, Y. Lubashevsky, D. G. Schlom, K. M. Shen, N. P. ArmtageComments: main text 5 pages, 3 figuresSubjects: Strongly Correlated Electrons (condmat.strel); Materials Science (condmat.mtrlsci)
SrRuO$_3$, a ferromagnet with an approximately 160\,K Curie temperature, exhibits a $T^2$ dependent dc resistivity below $\approx$ 30 K. Nevertheless, previous optical studies in the infrared and terahertz range show nonDrude dynamics at low temperatures which seem to contradict a Fermiliquid picture with longlived quasiparticles. In this work, we measure the lowfrequency THz range response of thin films with residual resistivity ratios, $\rho_{300K}/ \rho_{4K} \approx$ 74. Such low disorder samples allow an unprecedented look at the effects of electronelectron interactions on lowfrequency transport. At temperatures below 30 K, we found both a very sharp zerofrequency mode which has a width narrower than $k_BT/\hbar$ as well as a broader zero frequency Lorentzian that has at least an order of magnitude larger scattering rate. Both features have temperature dependencies consistent with a Fermiliquid with the wider feature explicitly showing a T$^2$ scaling. Such two Drude transport sheds light on previous reports of the violation of Mathielssen's rule and extreme sensitivity to disorder in metallic ruthenates. We consider a number of possibilities for the origin of the two feature optical conductivity including multiband effects that arise from momentum conserving interband scattering and the approximate conservation of a pseudomomentum that arises from quasi1D Fermi surfaces.
 [50] arXiv:2003.12026 [pdf]

Title: Diversity of anisotropy effects in the breakup of metallic FCC nanowires into ordered nanodroplet chainsComments: 18 pages, 6 figuresJournalref: CrystEngComm, March 2020Subjects: Mesoscale and Nanoscale Physics (condmat.meshall)
We have analyzed the expressed manifestation of the anisotropy of surface energy density in the dynamics of ultrathin nanowires, which break up into disjointed clusters when annealed below their melting temperature. The breakup process is studied for different temperatures and orientations of the nanowire axis relative to its internal crystal structure using the Monte Carlo kinetic method. We have also presented an approximate analytical model of the instability of nanowires. Generally, the interpretation of experimental results refers to the theoretical model developed by Nichols and Mullins, which is based on conceptions about the Rayleigh instability of liquid jets. In both cases, the theories  which do not take into account the anisotropy of surface energy density  predict the breakup of a nanowire/liquid jet with radius r into fragments with an average length {\Lambda}=9r. However, the observed value, {\Lambda}/r, often deviates from 9 either to lower values or to substantially greater ones (up to 2430). Our results explain various observed features of the breakup and the significant variations in the values of its parameter {\Lambda}/r depending on experimental conditions. In particular, the ambiguous role of exchange by atoms of the surface of a nanowire with the surrounding layer of free atoms formed as a result of their rather intensive sublimation, which occurs in a number of cases, has been investigated. We have shown that this exchange can lead both to a decrease, and to a significant increase, in the parameter {\Lambda}/r. The obtained results could be potentially useful in applications such as the development of optical waveguides based on ordered nanoparticles chains.
 [51] arXiv:2003.12036 [pdf, other]

Title: AnDi: The Anomalous Diffusion ChallengeAuthors: Gorka MuñozGil, Giovanni Volpe, Miguel Angel GarciaMarch, Ralf Metzler, Maciej Lewenstein, Carlo ManzoComments: 6 pages, 2 figure  AnDi Challenge webpage:Subjects: Statistical Mechanics (condmat.statmech); Computational Physics (physics.compph); Data Analysis, Statistics and Probability (physics.dataan); Quantitative Methods (qbio.QM)
The deviation from pure Brownian motion generally referred to as anomalous diffusion has received large attention in the scientific literature to describe many physical scenarios. Several methods, based on classical statistics and machine learning approaches, have been developed to characterize anomalous diffusion from experimental data, which are usually acquired as particle trajectories. With the aim to assess and compare the available methods to characterize anomalous diffusion, we have organized the Anomalous Diffusion (AnDi) Challenge (\url{}). Specifically, the AnDi Challenge will address three different aspects of anomalous diffusion characterization, namely: (i) Inference of the anomalous diffusion exponent. (ii) Identification of the underlying diffusion model. (iii) Segmentation of trajectories. Each problem includes subtasks for different number of dimensions (1D, 2D and 3D). In order to compare the various methods, we have developed a dedicated opensource framework for the simulation of the anomalous diffusion trajectories that are used for the training and test datasets. The challenge was launched on March 1, 2020, and consists of three phases. Currently, the participation to the first phase is open. Submissions will be automatically evaluated and the performance of the topscoring methods will be thoroughly analyzed and compared in an upcoming article.
 [52] arXiv:2003.12054 [pdf, ps, other]

Title: Thermodynamic properties of the onedimensional Ising model with magnetoelastic interactionSubjects: Statistical Mechanics (condmat.statmech); Mesoscale and Nanoscale Physics (condmat.meshall)
The Ising onedimensional (1D) chain with spin $S=1/2$ is studied with the lattice contribution included in the form of elastic interaction and thermal vibrations simultaneously taken into account. The magnetic energy term and the elastic (static) energy term based on the Morse potential are calculated exactly. The vibrational energy is calculated in the Debye approximation, in which the anharmonicity is introduced by the Gr{\"u}neisen parameter. The total Gibbs potential, including both the magnetic field, as well as the external force term, is constructed and from its minimum the equation of state is derived.
From the Gibbs energy all the thermodynamic properties are calculated in a selfconsistent manner. The comprehensive numerical calculations are performed in a full temperature range, i.e., from zero temperature up to the vicinity of melting. In particular, a role of magnetoelastic coupling is emphasized and examined. The numerical results are illustrated in figures and discussed.
Crosslists for Fri, 27 Mar 20
 [53] arXiv:2003.11550 (crosslist from hepth) [pdf, ps, other]

Title: Anomaly inflow and $p$form gauge theoriesComments: 123 pagesSubjects: High Energy Physics  Theory (hepth); Strongly Correlated Electrons (condmat.strel)
Chiral and nonchiral $p$form gauge fields have gravitational anomalies and anomalies of GreenSchwarz type. This means that they are most naturally realized as the boundary modes of bulk topological phases in one higher dimensions. We give a systematic description of the total bulkboundary system which is analogous to the realization of a chiral fermion on the boundary of a massive fermion. The anomaly of the boundary theory is given by the partition function of the bulk theory, which we explicitly compute in terms of the AtiyahPatodiSinger $\eta$invariant. We use our formalism to determine the $\mathrm{SL}(2,{\mathbb Z})$ anomaly of the 4d Maxwell theory. We also apply it to study the worldvolume theories of a single Dbrane and an M5brane in the presence of orientifolds, orbifolds, and Sfolds in string, M, and F theories. In an appendix we also describe a simple class of nonunitary invertible topological theories whose partition function is not a bordism invariant, illustrating the necessity of the unitarity condition in the cobordism classification of the invertible phases.
 [54] arXiv:2003.11556 (crosslist from quantph) [pdf, other]

Title: Thermodynamics of ultrastrongly coupled lightmatter systemsComments: 15 pages, 7 figuresSubjects: Quantum Physics (quantph); Other Condensed Matter (condmat.other)
We study the thermodynamic properties of a system of twolevel dipoles that are coupled ultrastrongly to a single cavity mode. By using exact numerical and approximate analytical methods, we evaluate the free energy of this system at arbitrary interaction strengths and discuss strongcoupling modifications of derivative quantities such as the specific heat or the electric susceptibility. From this analysis we identify the lowestorder cavityinduced corrections to those quantities in the collective ultrastrong coupling regime and show that for even stronger interactions the presence of a single cavity mode can strongly modify extensive thermodynamic quantities of a large ensemble of dipoles. In this nonperturbative coupling regime we also observe a significant shift of the ferroelectric phase transition temperature and a characteristic broadening and collapse of the blackbody spectrum of the cavity mode. Apart from a purely fundamental interest, these general insights will be important for identifying potential applications of ultrastrongcoupling effects, for example, in the field of quantum chemistry or for realizing quantum thermal machines.
 [55] arXiv:2003.11665 (crosslist from physics.appph) [pdf]

Title: Accurate Determination of Semiconductor Diffusion Coefficient Using Confocal MicroscopyComments: Main Text: 12 pages and 5 figures. Supporting Information: 7 pages and 6 figuresSubjects: Applied Physics (physics.appph); Materials Science (condmat.mtrlsci)
Confocal microscopy is a versatile tool capable of directly monitoring photoexcited carrier transport and recombination in thin film and single crystal samples. The diffusion coefficient, an important material property for designing efficient optoelectronic devices, is often determined by fitting the evolution of the photoexcited carrier population to a simplified Gaussian function. Although this model has gained widespread adoption, its application to different material systems and its sensitivity to various experimental conditions has not been explored. Here, we simulate the diffusive processes in metal halide perovskites and find that the diffusion coefficient can be inaccurately fit when higherorder processes, such as bimolecular and Auger recombination, dominate. Significant fitting error (> 5%) is introduced if the initial photoexcited carrier density exceeds 1x10$^1$$^7$ cm$^$$^3$ and if the material diffusion coefficient is less than ~ 1 cm$^2$ s$^$$^1$, both conditions commonly encountered in confocal microscopy measurements of perovskites. In addition, we find that grain size and grain boundaries present in polycrystalline thin films impact the carrier density temporal profiles, introducing more error in the diffusion coefficient fits. This analysis highlights important considerations in the interpretation of confocal microscopy data and provides critical steps towards the development of more robust diffusion models.
 [56] arXiv:2003.11745 (crosslist from hepth) [pdf, other]

Title: Quantum quench, large N, and symmetry restorationComments: 13 pages + appendicesSubjects: High Energy Physics  Theory (hepth); Statistical Mechanics (condmat.statmech)
We globally quench the theory of two dimensional massless fermions (many flavours) with quartic interactions by making the quartic coupling a smooth function of time. Working in a derivative expansion we show that the discrete Z2 symmetry in case of the GrossNeveu model, and the U(1) symmetry in case of the NambuJonaLasinio model, are restored during the zerotemperature quench. For the GrossNeveu model we show that this can be understood as an effective thermalization. The time of symmetry restoration shows scaling with the quench rate. We identify this with the KibbleZurek scaling in the problem. In a suitable double scaling limit, the symmetry restoration may be understood in terms of Liouville quantum mechanics.
 [57] arXiv:2003.11776 (crosslist from physics.appph) [pdf, other]

Title: Bipolar spin Hall nanooscillatorsAuthors: T. Hache, Y. Li, T. Weinhold, B. Scheumann, F. J. T. Gonçalves, O. Hellwig, J. Fassbender, H. SchultheissSubjects: Applied Physics (physics.appph); Materials Science (condmat.mtrlsci)
We demonstrate a novel type of spin Hall nanooscillator (SHNO) that allows for efficient tuning of magnetic autooscillations over an extended range of gigahertz frequencies, using bipolar direct currents at constant magnetic fields. This is achieved by stacking two distinct ferromagnetic layers with a platinum interlayer. In this device, the orientation of the spin polarised electrons accumulated at the top and bottom interfaces of the platinum layer is switched upon changing the polarity of the direct current. As a result, the effective antidamping required to drive large amplitude autooscillations can appear either at the top or bottom magnetic layer. Tuning of the autooscillation frequencies by several gigahertz can be obtained by combining two materials with sufficiently different saturation magnetization. Here we show that the combination of NiFe and CoFeB can result in 3 GHz shifts in the autooscillation frequencies. Bipolar SHNOs as such may bring enhanced synchronisation capabilities to neuromorphic computing applications.
 [58] arXiv:2003.11845 (crosslist from quantph) [pdf, other]

Title: Going beyond Local and Global approaches for localized thermal dissipationSubjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall)
Identifying which master equation is preferable for the description of a multipartite open quantum system is not trivial and has led in the recent years to the local vs. global debate in the context of Markovian dissipation. We treat here a paradigmatic scenario in which the system is composed of two interacting harmonic oscillators A and B, with only A interacting with a thermal bath  collection of other harmonic oscillators  and we study the equilibration process of the system initially in the ground state with the bath finite temperature. We show that the completely positive version of the Redfield equation obtained using coarsegrain and an appropriate timedependent convex mixture of the local and global solutions give rise to the most accurate semigroup approximations of the whole exact system dynamics, i.e. both at short and at long time scales, outperforming the local and global approaches.
 [59] arXiv:2003.11850 (crosslist from physics.optics) [pdf, other]

Title: The critical role of shell in enhanced fluorescence of metaldielectric coreshell nanoparticlesSubjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (condmat.meshall); Applied Physics (physics.appph); Chemical Physics (physics.chemph)
Large scale simulations are performed by means of the transfermatrix method to reveal optimal conditions for metaldielectric coreshell particles to induce the largest fluorescence on their surfaces. With commonly used plasmonic cores (Au and Ag) and dielectric shells (SiO2, Al2O3, ZnO), optimal core and shell radii are determined to reach maximum fluorescence enhancement for each wavelength within 550~850 nm (Au core) and 390~500 nm (Ag core) bands, in both air and aqueous hosts. The peak value of the maximum achievable fluorescence enhancement factors of coreshell nanoparticles, taken over entire wavelength interval, increases with the shell refractive index and can reach values up to 9 and 70 for Au and Ag cores, within 600~700 nm and 400~450 nm wavelength ranges, respectively, which is much larger than that for corresponding homogeneous metal nanoparticles. Replacing air by an aqueous host has a dramatic effect of nearly halving the sizes of optimal coreshell configurations at the peak value of the maximum achievable fluorescence. In the case of Au cores,the fluorescence enhancements for wavelengths within the first nearinfrared biological window (NIRI) between 700 and 900 nm can be improved twofold compared to homogeneous Au particle when the shell refractive index ns > 2. As a rule of thumb, the wavelength region of optimal fluorescence (maximal nonradiative decay) turns out to be redshifted (blueshifted) by as much as 50 nm relative to the localized surface plasmon resonance wavelength of corresponding optimized coreshell particle. Our results provide important design rules and general guidelines for enabling versatile platforms for imaging, light source, and biological applications.
 [60] arXiv:2003.11860 (crosslist from qbio.PE) [pdf, other]

Title: Attacking the Covid19 with the Isingmodel and the FermiDirac Distribution FunctionComments: 15 pages, 2 figures, 1 tableSubjects: Populations and Evolution (qbio.PE); Statistical Mechanics (condmat.statmech); Physics and Society (physics.socph)
We employ a spin $S$ = 1/2 Isinglike model and a FermiDiraclike function to describe the spread of Covid19. Our analysis, using the available official infections rate data reveals: $i$) that the epidemic curves, i.e., the number of reported cases $versus$ time, is welldescribed by a Gaussian function; $ii$) that the temporal evolution of the cumulative number of infected people follows a distorted FermiDiraclike distribution function; $iii$) the key role played by the quarantine in the prevention of the spread of Covid19 in terms of an $interacting$ parameter, which emulates the contact between infected and noninfected people. An analysis of the epidemic curves for Ebola, SARS, and Influenza A/H1N1 is also presented and described by a Gaussian function as well. Our findings demonstrate the universal character of wellestablished concepts in condensed matter Physics and their applications in different areas.
 [61] arXiv:2003.11874 (crosslist from condmat.mtrlsci) [pdf, ps, other]

Title: Electron spin relaxations of phosphorus donors in bulk silicon under large electric fieldComments: 7 pages, 5 figuresJournalref: Scientific Reports 9:2951 (2019)Subjects: Materials Science (condmat.mtrlsci); Applied Physics (physics.appph)
Modulation of donor electron wavefunction via electric fields is vital to quantum computing architectures based on donor spins in silicon. For practical and scalable applications, the donorbased qubits must retain sufficiently long coherence times in any realistic experimental conditions. Here, we present pulsed electron spin resonance studies on the longitudinal $(T_1)$ and transverse $(T_2)$ relaxation times of phosphorus donors in bulk silicon with various electric field strengths up to near avalanche breakdown in high magnetic fields of about 1.2 T and low temperatures of about 8 K. We find that the $T_1$ relaxation time is significantly reduced under large electric fields due to electric current, and $T_2$ is affected as the $T_1$ process can dominate decoherence. Furthermore, we show that the magnetoresistance effect in silicon can be exploited as a means to combat the reduction in the coherence times. While qubit coherence times must be much longer than quantum gate times, electrically accelerated $T_1$ can be found useful when qubit state initialization relies on thermal equilibration.
 [62] arXiv:2003.11887 (crosslist from quantph) [pdf, other]

Title: Probabilistic Hysteresis in an Isolated Quantum System: The Microscopic Onset of Irreversibility from a Quantum PerspectiveSubjects: Quantum Physics (quantph); Quantum Gases (condmat.quantgas)
Recently probabilistic hysteresis in isolated Hamiltonian systems of ultracold atoms has been studied in the limit of large particle numbers, where a semiclassical treatment is adequate. The origin of irreversibility in these sweep experiments, where a control parameter is slowly (adiabatically) tuned back and forth, turned out to be a passage blue back and forth across a separatrix (integrable case) or a passage in and out of a chaotic sea in phase space (chaotic case). Here we focus on the full quantum mechanical description of the integrable system and show how the semiclassical results emerge in the limit of large particle numbers. Instead of the crossing of a separatrix in phase space, where classical adiabaticity fails, the origin of irreversibility in the quantum system is a series of avoided crossings of the adiabatic energy levels: they become so close that already for modest particle numbers the change of the external parameter has to be unrealistically slow to reach the quantum adiabatic limit of perfectly reversible evolution. For a slow but finite sweep rate we find a broad regime where the quantum results agree with the semiclassical results, but only if besides the limit $N\to \infty$ an initial ensemble of states is considered, with sufficient initial energy width. For a single initial energy eigenstate we find in contrast that the backward sweep reveals strong quantum effects even for very large particle numbers.
 [63] arXiv:2003.11897 (crosslist from physics.appph) [pdf]

Title: Optical and electronic properties of colloidal CdSe Quantum RingsAuthors: James Xiao, Yun Liu, Violette Steinmetz, Mustafa Çağlar, Jeffrey Mc Hugh, Tomi Baikie, Nicolas Gauriot, Malgorzata Nguyen, Edoardo Ruggeri, Zahra AndajiGarmaroudi, Samuel D. Stranks, Laurent Legrand, Thierry Barisien, Richard H. Friend, Neil C. Greenham, Akshay Rao, Raj PandyaComments: 38 pages, 10 figuresSubjects: Applied Physics (physics.appph); Mesoscale and Nanoscale Physics (condmat.meshall); Materials Science (condmat.mtrlsci); Chemical Physics (physics.chemph); Quantum Physics (quantph)
Luminescent colloidal CdSe nanorings are a new type of semiconductor structure that have attracted interest due to the potential for unique physics arising from their nontrivial toroidal shape. However, the exciton properties and dynamics of these materials with complex topology are not yet well understood. Here, we use a combination of femtosecond vibrational spectroscopy, temperatureresolved photoluminescence (PL), and single particle measurements to study these materials. We find that on transformation of CdSe nanoplatelets to nanorings, by perforating the center of platelets, the emission lifetime decreases and the emission spectrum broadens due to ensemble variations in the ring size and thickness. The reduced PL quantum yield of nanorings (~10%) compared to platelets (~30%) is attributed to an enhanced coupling between: (i) excitons and CdSe LOphonons at 200 cm1 and (ii) negatively charged seleniumrich traps which give nanorings a high surface charge (~50 mV). Population of these weakly emissive trap sites dominates the emission properties with an increased trap emission at low temperatures relative to excitonic emission. Our results provide a detailed picture of the nature of excitons in nanorings and the influence of phonons and surface charge in explaining the broad shape of the PL spectrum and the origin of PL quantum yield losses. Furthermore, they suggest that the excitonic properties of nanorings are not solely a consequence of the toroidal shape but are also a result of traps introduced by puncturing the platelet center.
 [64] arXiv:2003.11925 (crosslist from quantph) [pdf, ps, other]

Title: Probabilistic magnetometry with twospin system in diamondSubjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall)
Solidstate magnetometers like the NitrogenVacancy center in diamond have been of paramount importance for the development of quantum sensing with nanoscale spatial resolution. The basic protocol is a Ramsey sequence, that imprints an external static magnetic field into phase of the quantum sensor, which is subsequently readout. In this work we show that the hyperfine coupling between the NitrogenVacancy and a nearby Carbon13 can be used to set a postselection protocol that leads to an enhancement of the sensitivity under realistic experimental conditions. We found that for an isotopically purified sample the detection of weak magnetic fields in the $\mu$T range can be achieved with a sensitivity of few nTHz$^{1/2}$ at cryogenic temperature ($4$ K), and $0.1$ $\mu$THz$^{1/2}$ at room temperature.
 [65] arXiv:2003.11933 (crosslist from physics.compph) [pdf, other]

Title: Spin textures in chiral magnetic monolayers with suppressed nearestneighbor exchangeSubjects: Computational Physics (physics.compph); Strongly Correlated Electrons (condmat.strel)
High tunability of two dimensional magnetic materials (by strain, gating, heterostructuring or otherwise) provides unique conditions for studying versatile magnetic properties and controlling emergent magnetic phases. Expanding the scope of achievable magnetic phenomena in such materials is important for both fundamental and technological advances. Here we perform atomistic spindynamics simulations to explore the (chiral) magnetic phases of atomic monolayers in the limit of suppressed firstneighbors exchange interaction. We report the rich phase diagram of exotic magnetic configurations, obtained for both square and honeycomb lattice symmetries, comprising coexistence of ferromagnetic and antiferromagnetic spincycloids, as well as multiple types of magnetic skyrmions. We perform a minimumenergy path analysis for the skyrmion collapse to evaluate the stability of such topological objects, and reveal that magnetic monolayers could be good candidates to host the antiferromagnetic skyrmions that are experimentally evasive to date.
 [66] arXiv:2003.11996 (crosslist from cs.NE) [pdf, other]

Title: Accelerated Analog Neuromorphic ComputingSubjects: Neural and Evolutionary Computing (cs.NE); Disordered Systems and Neural Networks (condmat.disnn); Neurons and Cognition (qbio.NC)
This paper presents the concepts behind the BrainScales (BSS) accelerated analog neuromorphic computing architecture. It describes the secondgeneration BrainScales2 (BSS2) version and its most recent insilico realization, the HICANNX Application Specific Integrated Circuit (ASIC), as it has been developed as part of the neuromorphic computing activities within the European Human Brain Project (HBP). While the first generation is implemented in an 180nm process, the second generation uses 65nm technology. This allows the integration of a digital plasticity processing unit, a highlyparallel micro processor specially built for the computational needs of learning in an accelerated analog neuromorphic systems. The presented architecture is based upon a continuoustime, analog, physical model implementation of neurons and synapses, resembling an analog neuromorphic accelerator attached to buildin digital compute cores. While the analog part emulates the spikebased dynamics of the neural network in continuoustime, the latter simulates biological processes happening on a slower timescale, like structural and parameter changes. Compared to biological timescales, the emulation is highly accelerated, i.e. all timeconstants are several orders of magnitude smaller than in biology. Programmable ion channel emulation and intercompartmental conductances allow the modeling of nonlinear dendrites, backpropagating actionpotentials as well as NMDA and Calcium plateau potentials. To extend the usability of the analog accelerator, it also supports vectormatrix multiplication. Thereby, BSS2 supports inference of deep convolutional networks as well as locallearning with complex ensembles of spiking neurons within the same substrate.
 [67] arXiv:2003.12051 (crosslist from physics.atomph) [pdf, ps, other]

Title: Accurate ab initio properties of the NaLi molecule in the $a^3Σ^+$ electronic stateComments: 7 pages, 2 figures, 2 tablesSubjects: Atomic Physics (physics.atomph); Quantum Gases (condmat.quantgas); Chemical Physics (physics.chemph); Quantum Physics (quantph)
We calculate the electronic and rovibrational structure of the 14electron ${}^{23}$Na${}^6$Li molecule in the $a^3\Sigma^+$ state with spectroscopic accuracy ($<0.5\,$cm$^{1}$) using stateoftheart ab initio methods of quantum chemistry. We show that the inclusion of higherlevel excitations, coreelectron correlation, relativistic, QED, and adiabatic corrections is necessary to reproduce accurately scattering and spectroscopic properties of alkalimetal systems. We obtain the well depth, $D_e=229.9(5)\,$cm$^{1}$, the dissociation energy, $D_0=208.2(5)\,$cm$^{1}$, and the scattering length, $a_s=84^{+25}_{41}\,$bohr, in good agreement with recent experimental measurements. These values are obtained without any adjustment to experimental data, showing that quantum chemistry methods are capable of predicting scattering properties of manyelectron systems, provided relatively weak interaction and small reduced mass of the system.
 [68] arXiv:2003.12055 (crosslist from qbio.PE) [pdf, other]

Title: Agestructured impact of social distancing on the COVID19 epidemic in IndiaComments: Code and updates at 9 pages, 5 figures, and 2 tablesSubjects: Populations and Evolution (qbio.PE); Statistical Mechanics (condmat.statmech)
The outbreak of the novel coronavirus, COVID19, has been declared a pandemic by the WHO. The structures of social contact critically determine the spread of the infection and, in the absence of vaccines, the control of these structures through largescale social distancing measures appears to be the most effective means of mitigation. Here we use an agestructured SIR model with social contact matrices obtained from surveys and Bayesian imputation to study the progress of the COVID19 epidemic in India. The basic reproductive ratio R0 and its timedependent generalization are computed based on case data, age distribution and social contact structure. The impact of social distancing measures  workplace nonattendance, school closure, lockdown  and their efficacy with durations are then investigated. A threeweek lockdown is found insufficient to prevent a resurgence and, instead, protocols of sustained lockdown with periodic relaxation are suggested. Forecasts are provided for the reduction in agestructured morbidity and mortality as a result of these measures. Our study underlines the importance of age and social contact structures in assessing the countryspecific impact of mitigatory social distancing.
Replacements for Fri, 27 Mar 20
 [69] arXiv:1703.07358 (replaced) [pdf, other]

Title: Highdensity quantum sensing with dissipative first order transitionsComments: 6+3 pages, 6+3 figuresJournalref: Phys. Rev. Lett. 120, 150501 (2018)Subjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall); Statistical Mechanics (condmat.statmech)
 [70] arXiv:1810.02446 (replaced) [pdf, other]

Title: Physical Origin of the OneQuarter Exact Exchange in Density Functional TheoryAuthors: Marco BernardiSubjects: Materials Science (condmat.mtrlsci); Chemical Physics (physics.chemph)
 [71] arXiv:1811.00555 (replaced) [pdf, other]

Title: Floquet HigherOrder Topological Insulators with Anomalous Dynamical PolarizationComments: 4+2+18 pages, major update for a new anomalous dynamical polarization theorySubjects: Strongly Correlated Electrons (condmat.strel); Quantum Gases (condmat.quantgas)
 [72] arXiv:1901.02019 (replaced) [pdf, other]

Title: Initialization of quantum simulators by sympathetic coolingComments: 8+4 pages, 6+5 figuresJournalref: Sci. Adv. 6, eaaw9268 (2020)Subjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall); Atomic Physics (physics.atomph)
 [73] arXiv:1902.07759 (replaced) [pdf, other]

Title: Generalized wavepacket model for studying coherence of matterwave interferometersAuthors: Yonathan JaphaComments: 24 pages, 8 figuresSubjects: Quantum Gases (condmat.quantgas); Quantum Physics (quantph)
 [74] arXiv:1905.02173 (replaced) [pdf, other]

Title: Assisted concentration of Gaussian resourcesComments: 21 pages, 3 figures. In v2 we changed the title and added the new Figures 1 and 2, illustrating the oneway and twoway Gaussian collaboration protocols, respectivelySubjects: Quantum Physics (quantph); Other Condensed Matter (condmat.other); Mathematical Physics (mathph)
 [75] arXiv:1905.03090 (replaced) [pdf, other]

Title: Kondoinduced giant isotropic negative thermal expansionAuthors: D. G. Mazzone, M. Dzero, M. Abeykoon, H. Yamaoka, H. Ishii, N. Hiraoka, J. P. Rueff, J. Ablett, K. Imura, H. S. Suzuki, J. N. Hancock, I. JarrigeSubjects: Strongly Correlated Electrons (condmat.strel)
 [76] arXiv:1906.06317 (replaced) [pdf, other]

Title: freud: A Software Suite for High Throughput Analysis of Particle Simulation DataAuthors: Vyas Ramasubramani, Bradley D. Dice, Eric S. Harper, Matthew P. Spellings, Joshua A. Anderson, Sharon C. GlotzerComments: GitHub repository: ; Documentation: ; Accepted for publication in Computer Physics CommunciationSubjects: Computational Physics (physics.compph); Materials Science (condmat.mtrlsci); Computational Engineering, Finance, and Science (cs.CE)
 [77] arXiv:1907.01111 (replaced) [pdf, other]

Title: How trapped particles interact with and sample superfluid vortex excitationsComments: 13 pages, 7 figuresSubjects: Other Condensed Matter (condmat.other); Fluid Dynamics (physics.fludyn)
 [78] arXiv:1907.07079 (replaced) [pdf, other]

Title: Simulation methods for open quantum manybody systemsComments: revised versionSubjects: Quantum Physics (quantph); Strongly Correlated Electrons (condmat.strel); Computational Physics (physics.compph)
 [79] arXiv:1907.11610 (replaced) [pdf, other]

Title: Collapse of layer dimerization in the photoinduced hidden state of 1TTaS2Authors: Quirin Stahl, Maximilian Kusch, Florian Heinsch, Gaston Garbarino, Norman Kretzschmar, Kerstin Hanff, Kai Rossnagel, Jochen Geck, Tobias RitschelJournalref: Nat Commun 11, 1247 (2020)Subjects: Strongly Correlated Electrons (condmat.strel)
 [80] arXiv:1908.06977 (replaced) [pdf, ps, other]

Title: Superfluids as Higherform AnomaliesComments: 29 pages; v3 corrected Eq. (1.25), published versionSubjects: High Energy Physics  Theory (hepth); Strongly Correlated Electrons (condmat.strel)
 [81] arXiv:1909.05281 (replaced) [pdf]

Title: Chemical bonding in chalcogenides: the concept of multicentre hyperbondingComments: 4 figuresSubjects: Materials Science (condmat.mtrlsci)
 [82] arXiv:1909.05802 (replaced) [pdf, other]

Title: Ecological communities from random generalised LotkaVolterra dynamics with nonlinear feedbackComments: 48 pages, 11 figuresJournalref: Phys. Rev. E 101, 032101 (2020)Subjects: Populations and Evolution (qbio.PE); Disordered Systems and Neural Networks (condmat.disnn); Statistical Mechanics (condmat.statmech)
 [83] arXiv:1910.01134 (replaced) [pdf, ps, other]

Title: Unifying Lattice Models, Links and Quantum Geometric Langlands via Branes in String TheoryComments: 31 pages. Typo correctedSubjects: High Energy Physics  Theory (hepth); Statistical Mechanics (condmat.statmech); Geometric Topology (math.GT); Quantum Algebra (math.QA); Representation Theory (math.RT)
 [84] arXiv:1910.07759 (replaced) [pdf, ps, other]

Title: Unusual slow magnetic fluctuations and critical slowing down in Sr$_{2}$Ir$_{1x}$Rh$_{x}$O$_{4}$Authors: C. Tan, Z. F. Ding, J. Zhang, Z. H. Zhu, O. O. Bernal, P.C. Ho, A. D. Hillier, A. Koda, H. Luetkens, G. D. Morris, D. E. MacLaughlin, L. ShuSubjects: Strongly Correlated Electrons (condmat.strel)
 [85] arXiv:1911.04187 (replaced) [pdf, other]

Title: Signatures of unconventional pairing in spinimbalanced onedimensional fewfermion systemsJournalref: Physical Review Research 2, 012077(R) (2020)Subjects: Quantum Gases (condmat.quantgas); Superconductivity (condmat.suprcon); Quantum Physics (quantph)
 [86] arXiv:1911.12340 (replaced) [pdf, other]

Title: Elastoviscoplastic rheology and ageing in a simplified soft glassy constitutive modelAuthors: Suzanne M. FieldingComments: 15 pages, 9 figures; version accepted, Journal of RheologySubjects: Soft Condensed Matter (condmat.soft)
 [87] arXiv:1912.01207 (replaced) [pdf, ps, other]

Title: Straininduced enhancement of the Seebeck effect in magnetic tunneling junctions via interface resonant tunneling: Abinitio studyComments: 9 pages, 10 figures, published versionJournalref: Phys. Rev. B 101, 094430 (2020)Subjects: Materials Science (condmat.mtrlsci); Mesoscale and Nanoscale Physics (condmat.meshall)
 [88] arXiv:1912.05230 (replaced) [pdf, other]

Title: First Principles Heisenberg Models of 2D magnetic materials: The Importance of Quantum Corrections to the Exchange CouplingComments: Version 3. Modified expression for singleion anisotropy to make the sign of the spinwave consistent with the sign of the magnetic anisotropy. Numbers in tables changed slightly according to the modificationSubjects: Materials Science (condmat.mtrlsci); Mesoscale and Nanoscale Physics (condmat.meshall)
 [89] arXiv:1912.06799 (replaced) [pdf]

Title: Spinmediated chargetoheat current conversion phenomena in ferromagnetic binary alloysComments: 21 pages, 14 figuresJournalref: Physical Review Materials 4, 034409 (2020)Subjects: Materials Science (condmat.mtrlsci)
 [90] arXiv:2001.07419 (replaced) [pdf, other]

Title: Progress in cooling nanoelectronic devices to ultralow temperaturesComments: 19 pages, 13 figuresSubjects: Mesoscale and Nanoscale Physics (condmat.meshall)
 [91] arXiv:2001.08461 (replaced) [pdf, other]

Title: Exfoliated hexagonal BN as gate dielectric for InSb nanowire quantum dots with improved gate hysteresis and charge noiseAuthors: Felix Jekat, Benjamin Pestka, Diana Car, Saša Gazibegović, Kilian Flöhr, Sebastian Heedt, Jürgen Schubert, Marcus Liebmann, Erik P. A. M. Bakkers, Thomas Schäpers, Markus MorgensternSubjects: Mesoscale and Nanoscale Physics (condmat.meshall)
 [92] arXiv:2001.09194 (replaced) [pdf, ps, other]

Title: Ab initio manybody GW correlations in the electronic structure of LaNiO$_2$Comments: 6 pages, 6 figures, 2 tablesSubjects: Superconductivity (condmat.suprcon); Materials Science (condmat.mtrlsci)
 [93] arXiv:2002.03771 (replaced) [pdf, ps, other]

Title: Two universal laws for plastic flows and the consistent thermodynamic dislocation theoryAuthors: Khanh Chau LeComments: 8 pages, 2 figuresSubjects: Materials Science (condmat.mtrlsci)
 [94] arXiv:2002.06192 (replaced) [pdf, other]

Title: Signatures of topological ground state degeneracy in Majorana islandsComments: 27 pages, 6 figures. Submitted versionSubjects: Superconductivity (condmat.suprcon); Mesoscale and Nanoscale Physics (condmat.meshall)
 [95] arXiv:2002.08589 (replaced) [pdf]

Title: Intense Dark Exciton Emission from Strongly Quantum Confined CsPbBr$_3$ NanocrystalsAuthors: Daniel Rossi, Xiaohan Liu, Yangjin Lee, Mohit Khurana, Joseph Puthenpurayil, Kwanpyo Kim, Alexey Akimov, Jinwoo Cheon, Dong Hee SonSubjects: Applied Physics (physics.appph); Materials Science (condmat.mtrlsci)
 [96] arXiv:2003.02423 (replaced) [pdf]

Title: Gatetunable van der Waals heterostructure for reconfigurable neural network vision sensorAuthors: ChenYu Wang, ShiJun Liang, Shuang Wang, Pengfei Wang, Zhuan Li, Zhongrui Wang, Anyuan Gao, Chen Pan, Chuan Liu, Jian Liu, Huafeng Yang, Xiaowei Liu, Wenhao Song, Cong Wang, Xiaomu Wang, Kunji Chen, Zhenlin Wang, Kenji Watanabe, Takashi Taniguchi, J. Joshua Yang, Feng MiaoComments: 20 pages, 4 figuresSubjects: Materials Science (condmat.mtrlsci); Disordered Systems and Neural Networks (condmat.disnn); Mesoscale and Nanoscale Physics (condmat.meshall); Applied Physics (physics.appph)
 [97] arXiv:2003.03555 (replaced) [pdf]

Title: Honeycomb Layered Oxides: Structure, Energy Storage, Transport, Topology and Relevant InsightsAuthors: Godwill Mbiti Kanyolo, Titus Masese, Nami Matsubara, ChihYao Chen, Josef Rizell, Ola Kenji Forslund, Elisabetta Nocerino, Konstantinos Papadopoulos, Anton Zubayer, Minami Kato, Kohei Tada, Keigo Kubota, Hiroshi Senoh, ZhenDong Huang, Yasmine Sassa, Martin Mansson, Hajime Matsumoto, Qiang XuComments: 55 pages, 8 figures, 1 cover art, Review ManuscriptSubjects: Materials Science (condmat.mtrlsci)
 [98] arXiv:2003.04885 (replaced) [pdf, other]

Title: Flux noise in superconducting qubits and the gap states continuumComments: 6 pages, 2 figuresSubjects: Superconductivity (condmat.suprcon)
 [99] arXiv:2003.05566 (replaced) [pdf, ps, other]

Title: Ion Modes in Dense Ionized Plasmas through NonAdiabatic Molecular DynamicsComments: 5 pages and 4 figures in the main manuscript, 6 pages and 9 figures in the supplementary information; typos corrected; corrected grammar, references fixed, author name adjustedSubjects: Plasma Physics (physics.plasmph); Statistical Mechanics (condmat.statmech); Computational Physics (physics.compph)
 [100] arXiv:2003.07261 (replaced) [pdf, other]

Title: Protected helical transport in magnetically doped quantum wires: beyond the 1D paradigmComments: Slightly polished version, improved bibliographySubjects: Strongly Correlated Electrons (condmat.strel); Mesoscale and Nanoscale Physics (condmat.meshall)
 [101] arXiv:2003.07834 (replaced) [pdf, other]

Title: Fractional viscoelastic models for powerlaw materialsComments: 28 pages, 12 figuresSubjects: Soft Condensed Matter (condmat.soft); Biological Physics (physics.bioph); Quantitative Methods (qbio.QM); Tissues and Organs (qbio.TO)
 [102] arXiv:2003.10364 (replaced) [pdf]

Title: OpticalField Driven ChargeTransfer Modulations near Composite NanostructuresAuthors: Kwang Jin Lee, Elke Beyreuther, Sohail A. Jalil, Sang Jun Kim, Lukas Eng, Chunlei Guo, Pascal AndreComments: 8 pages, 6 figuresSubjects: Materials Science (condmat.mtrlsci); Soft Condensed Matter (condmat.soft); Chemical Physics (physics.chemph)
 [103] arXiv:2003.11130 (replaced) [pdf, other]

Title: Thermal Hall effect in the pseudogap phase of cupratesAuthors: Chandra M. VarmaSubjects: Strongly Correlated Electrons (condmat.strel)
 [104] arXiv:2003.11168 (replaced) [pdf, other]

Title: Measurementbased cooling of a nonlinear mechanical resonatorComments: 8 pages, 5 figuresSubjects: Quantum Physics (quantph); Mesoscale and Nanoscale Physics (condmat.meshall)
 [105] arXiv:2003.11532 (replaced) [pdf, other]

Title: Managing Flow of Liquid LightComments: 5 pages, 4 figuresSubjects: Quantum Gases (condmat.quantgas); Mesoscale and Nanoscale Physics (condmat.meshall); Pattern Formation and Solitons (nlin.PS); Optics (physics.optics)
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