Found 48 papers in cond-mat
Date of feed: Thu, 06 Jul 2023 00:30:00 GMT

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Polar coherent states in bilayer graphene under a constant uniform magnetic field. (arXiv:2307.01213v1 [cond-mat.mes-hall])
D.I. Martínez Moreno, J. Negro, L.M. Nieto

Symmetries associated with the Hamiltonian describing bilayer graphene subjected to a constant magnetic field perpendicular to the plane of the bilayer are calculated using polar coordinates. These symmetries are then applied to explain some fundamental properties, such as the spectrum and the integer pseudo-spin character of the eigenfunctions. The probability and current densities of the bilayer Hamiltonian have also been calculated in polar coordinates and shown to be gauge invariant and scalar under generalized rotations. We also define appropriate coherent states of this system as eigenfunctions, with complex eigenvalues, of a suitable chose annihilation operator. In this framework, symmetries are also useful to show the meaning of the complex eigenvalue in terms of expected values. The local current density of these coherent states is shown to exhibit a kind of radial component interference effect, something that has gone unnoticed until now. Some of these results that have just been exposed are graphically illustrated throughout the manuscript.

Unveiling Real Triple Degeneracies in Crystals: Exploring Link and Compound Structures. (arXiv:2307.01228v1 [cond-mat.mes-hall])
Wenwen Liu, Hanyu Wang, Biao Yang, Shuang Zhang

With their non-Abelian topological charges, real multi-bandgap systems challenge the conventional topological phase classifications. As the minimal sector of multi-bandgap systems, real triple degeneracies (RTPs), which serves as real "Weyl points", lay the foundation for the research on real topological phases. However, experimental observation of RTP and physical systems with global band configuration consisting of multiple RTPs in crystals has not been reported. In this study, we employ Euler number to characterize RTPs, establish their connection with both Abelian and non-Abelian charges, and provide experimental evidence for the existence of RTPs in photonic meta-crystals. By considering RTPs as the basic elements, we further propose the concept of a topological compound, akin to a chemical compound, where we find that certain phases are not topologically allowed. The topological classification of RTPs in crystals demonstrated in our work plays a similar role as the "no-go" theorem in the Weyl system.

Geometric Stiffness in Interlayer Exciton Condensates. (arXiv:2307.01253v1 [cond-mat.mes-hall])
Nishchhal Verma, Daniele Guerci, Raquel Queiroz

Recent experiments have confirmed the presence of interlayer excitons in the ground state of transition metal dichalcogenide (TMD) bilayers. The interlayer excitons are expected to show remarkable transport properties when they undergo Bose condensation. In this work, we demonstrate that quantum geometry of Bloch wavefunctions plays an important role in the phase stiffness of the Interlayer Exciton Condensate (IEC). Notably, we identify a geometric contribution that amplifies the stiffness, leading to the formation of a robust condensate with an increased BKT temperature. Our results have direct implications for the ongoing experimental efforts on interlayer excitons in materials that have non-trivial geometry. We provide quantitative estimates for the geometric contribution in TMD bilayers through a realistic continuum model with gated Coulomb interaction, and find that the substantially increased stiffness allows for an IEC to be realized at amenable experimental conditions.

Nontrivial worldline winding in non-Hermitian quantum systems. (arXiv:2307.01260v1 [quant-ph])
Shi-Xin Hu, Yongxu Fu, Yi Zhang

Amid the growing interest in non-Hermitian quantum systems, non-interacting models have received the most attention. Here, through the stochastic series expansion quantum Monte Carlo method, we investigate non-Hermitian physics in interacting quantum systems, e.g., various non-Hermitian quantum spin chains. While calculations yield consistent numerical results under open boundary conditions, non-Hermitian quantum systems under periodic boundary conditions observe an unusual concentration of imaginary-time worldlines over nontrivial winding and require enhanced ergodicity between winding-number sectors for proper convergences. Such nontrivial worldline winding is an emergent physical phenomenon that also exists in other non-Hermitian models and analytical approaches. Alongside the non-Hermitian skin effect and the point-gap spectroscopy, it largely extends the identification and analysis of non-Hermitian topological phenomena to quantum systems with interactions, finite temperatures, biorthogonal basis, and periodic boundary conditions in a novel and controlled fashion. Finally, we study the direct physical implications of such nontrivial worldline winding, which bring additional, potentially quasi-long-range contributions to the entanglement entropy.

Symmetry fractionalization, mixed-anomalies and dualities in quantum spin models with generalized symmetries. (arXiv:2307.01266v1 [cond-mat.str-el])
Heidar Moradi, Ömer M. Aksoy, Jens H. Bardarson, Apoorv Tiwari

We investigate the gauging of higher-form finite Abelian symmetries and their sub-groups in quantum spin models in spatial dimensions $d=2$ and 3. Doing so, we naturally uncover gauged models with dual higher-group symmetries and potential mixed 't Hooft anomalies. We demonstrate that the mixed anomalies manifest as the symmetry fractionalization of higher-form symmetries participating in the mixed anomaly. Gauging is realized as an isomorphism or duality between the bond algebras that generate the space of quantum spin models with the dual generalized symmetry structures. We explore the mapping of gapped phases under such gauging related dualities for 0-form and 1-form symmetries in spatial dimension $d=2$ and 3. In $d=2$, these include several non-trivial dualities between short-range entangled gapped phases with 0-form symmetries and 0-form symmetry enriched Higgs and (twisted) deconfined phases of the gauged theory with possible symmetry fractionalizations. Such dualities also imply strong constraints on several unconventional, i.e., deconfined or topological transitions. In $d=3$, among others, we find, dualities between topological orders via gauging of 1-form symmetries. Hamiltonians self-dual under gauging of 1-form symmetries host emergent non-invertible symmetries, realizing higher-categorical generalizations of the Tambara-Yamagami fusion category.

Sequential Quantum Circuits as Maps between Gapped Phases. (arXiv:2307.01267v1 [cond-mat.str-el])
Xie Chen, Arpit Dua, Michael Hermele, David T. Stephen, Nathanan Tantivasadakarn, Robijn Vanhove, Jing-Yu Zhao

Finite-depth quantum circuits preserve the long-range entanglement structure in quantum states and map between states within a gapped phase. To map between states of different gapped phases, we can use Sequential Quantum Circuits which apply unitary transformations to local patches, strips, or other sub-regions of a system in a sequential way. The sequential structure of the circuit on the one hand preserves entanglement area law and hence the gapped-ness of the quantum states. On the other hand, the circuit has generically a linear depth, hence it is capable of changing the long-range correlation and entanglement of quantum states and the phase they belong to. In this paper, we discuss systematically the definition, basic properties, and prototypical examples of sequential quantum circuits that map product states to GHZ states, symmetry-protected topological states, intrinsic topological states, and fracton states. We discuss the physical interpretation of the power of the circuits through connection to condensation, Kramers-Wannier duality, and the notion of foliation for fracton phases.

High-Strength Amorphous Silicon Carbide for Nanomechanics. (arXiv:2307.01271v1 [cond-mat.mes-hall])
Minxing Xu, Dongil Shin, Paolo M. Sberna, Roald van der Kolk, Andrea Cupertino, Miguel A. Bessa, Richard A. Norte

For decades, mechanical resonators with high sensitivity have been realized using thin-film materials under high tensile loads. Although there have been remarkable strides in achieving low-dissipation mechanical sensors by utilizing high tensile stress, the performance of even the best strategy is limited by the tensile fracture strength of the resonator materials. In this study, a wafer-scale amorphous thin film is uncovered, which has the highest ultimate tensile strength ever measured for a nanostructured amorphous material. This silicon carbide (SiC) material exhibits an ultimate tensile strength of over 10 GPa, reaching the regime reserved for strong crystalline materials and approaching levels experimentally shown in graphene nanoribbons. Amorphous SiC strings with high aspect ratios are fabricated, with mechanical modes exceeding quality factors 10^8 at room temperature, the highest value achieved among SiC resonators. These performances are demonstrated faithfully after characterizing the mechanical properties of the thin film using the resonance behaviors of free-standing resonators. This robust thin-film material has significant potential for applications in nanomechanical sensors, solar cells, biological applications, space exploration and other areas requiring strength and stability in dynamic environments. The findings of this study open up new possibilities for the use of amorphous thin-film materials in high-performance applications.

Wavefunction tomography of topological dimer chains with long-range couplings. (arXiv:2307.01283v1 [physics.optics])
F. Pellerin, R. Houvenaghel, W. A. Coish, I. Carusotto, P. St-Jean

The ability to tailor with a high accuracy the inter-site connectivity in a lattice is a crucial tool for realizing novel topological phases of matter. Here, we report the experimental realization of photonic dimer chains with long-range hopping terms of arbitrary strength and phase, providing a rich generalization of the celebrated Su-Schrieffer-Heeger model. Our experiment is based on a synthetic dimension scheme involving the frequency modes of an optical fiber loop platform. This setup provides direct access to both the band dispersion and the geometry of the Bloch wavefunctions throughout the entire Brillouin zone allowing us to extract the winding number for any possible configuration. Finally, we highlight a topological phase transition solely driven by a time-reversal-breaking synthetic gauge field associated with the phase of the long-range hopping, providing a route for engineering topological bands in photonic lattices belonging to the AIII symmetry class.

Charge-polarization coupling in the nanostructure "thin Hf$_x$Zr$_{1-x}$O$_2$ film - graphene". (arXiv:2307.01363v1 [cond-mat.mtrl-sci])
Anna N. Morozovska, Maksym V. Strikha, Kyle P. Kelley, Sergei V. Kalinin, Eugene A. Eliseev

To describe the charge-polarization coupling in the nanostructure formed by a thin Hf$_x$Zr$_{1-x}$O$_2$ film with a single-layer graphene as a top electrode, we develop the phenomenological effective Landau-Ginzburg-Devonshire model. This approach is based on the parametrization of the Landau expansion coefficients for the polar and antipolar orderings in thin Hf$_x$Zr$_{1-x}$O$_2$ films from a limited number of polarization-field curves and hysteresis loops. The Landau expansion coefficients are nonlinearly dependent on the film thickness $h$ and Zr/[Hf+Zr] ratio $x$, in contrast to h-independent and linearly $x$-dependent expansion coefficients of a classical Landau energy. We explain the dependence of the Landau expansion coefficients by the strong nonmonotonic dependence of the Hf$_x$Zr$_{1-x}$O$_2$ film polar properties on the film thickness, grain size and surface energy. The proposed Landau free energy with five "effective" expansion coefficients, which are interpolation functions of $x$ and $h$, describes the continuous transformation of polarization dependences on applied electric field and hysteresis loop shapes induced by the changes of $x$ and $h$ in the range $0 < x < 1$ and 5 nm < $h$ < 35 nm. Using this effective free energy, we demonstrated that the polarization of Hf$_x$Zr$_{1-x}$O$_2$ film influences strongly on the graphene conductivity, and the full correlation between the distribution of polarization and charge carriers in graphene is revealed. In accordance with our modeling, the polarization of the (5 - 25) nm thick Hf$_x$Zr$_{1-x}$O$_2$ films, which are in the ferroelectric-like or antiferroelectric-like states for the chemical compositions $0.35 < x < 0.95$, determine the concentration of carriers in graphene and can control its field dependence. The result can be promising for creation of next generation Si-compatible nonvolatile memories and graphene-ferroelectric FETs.

Normal state magneto transport properties of FeSe$_{0.5}$Te$_{0.5}$ superconductor: The role of topological surface states. (arXiv:2307.01476v1 [cond-mat.supr-con])
M.M. Sharma, N. K. Karn, V.P.S. Awana (Csir-Npl, India)

Doped Iron Chalcogenide (FeCh) superconductors are extensively studied in the context of topological superconductivity. However, the evidence of topological surface states in electrical transport measurements of the doped FeCh system is yet warranted. In the present letter, we performed angle-dependent magneto transport measurements on a single crystal of a doped FeCh system, i.e., FeSe$_{0.5}$Te$_{0.5}$. A non-saturating linear magnetoresistance (MR) has been observed under the magnetic field up to 14 T in the normal state of FeSe$_{0.5}$Te$_{0.5}$. The MR is shown to possess anisotropy, which indicates the presence of topological surface states in FeSe$_{0.5}$Te$_{0.5}$. Angle-dependent Magneto-conductivity (MC) at low magnetic fields has been modelled by Hikami Larkin Nagaoka (HLN) formalism, which shows the presence of weak antilocalization (WAL) effect in FeSe$_{0.5}$Te$_{0.5}$. The observed WAL effect is found to be 2D in nature through angle-dependent magneto transport measurements. Theoretical calculations based on Density Functional Theory (DFT) are also performed to get more confidence on the presence of topological surface states in FeSe$_{0.5}$Te$_{0.5}$.

Electrical conductivity of crack-template-based transparent conductive films: A computational point of view. (arXiv:2307.01509v1 [cond-mat.dis-nn])
Yuri Yu. Tarasevich, Andrei V. Eserkepov, Irina V. Vodolazskaya

Crack-template-based transparent conductive films (TCFs) are promising kinds of junction-free, metallic network electrodes that can be used, e.g., for transparent electromagnetic interference (EMI) shielding. Using image processing of published photos of TCFs, we have analyzed the topological and geometrical properties of such crack templates. Additionally, we analyzed the topological and geometrical properties of some computer-generated networks. We computed the electrical conductance of such networks against the number density of their cracks. Comparison of these computations with predictions of the two analytical approaches revealed the proportionality of the electrical conductance to the square root of the number density of the cracks was found, this being consistent with the theoretical predictions.

Efficient computation of optical excitations in two-dimensional materials with the Xatu code. (arXiv:2307.01572v1 [cond-mat.mtrl-sci])
Alejandro José Uría-Álvarez, Juan José Esteve-Paredes, Manuel Antonio García-Blázquez, Juan José Palacios

Here we describe an efficient numerical implementation of the Bethe-Salpeter equation to obtain the excitonic spectrum of semiconductors. This is done on the electronic structure calculated either at the simplest tight-binding level or through density funcional theory calculations based on local orbitals. We use a simplified model for the electron-electron interactions which considers atomic orbitals as point-like orbitals and a phenomenological screening. The optical conductivity can then be optionally computed within the Kubo formalism. Our results for paradigmatic two-dimensional materials such as hBN and MoS2, when compared with those of more sophisticated first-principles methods, are excellent and envision a practical use of our implementation beyond the computational limitations of such methods.

Logarithmically enhanced area-laws for fermions in vanishing magnetic fields in dimension two. (arXiv:2307.01699v1 [math-ph])
Paul Pfeiffer, Wolfgang Spitzer

We consider fermionic ground states of the Landau Hamiltonian, $H_B$, in a constant magnetic field of strength $B>0$ in $\mathbb R^2$ at some fixed Fermi energy $\mu>0$, described by the Fermi projection $P_B:= 1(H_B\le \mu)$. For some fixed bounded domain $\Lambda\subset \mathbb{R}^2$ with boundary set $\partial\Lambda$ and an $L>0$ we restrict these ground states spatially to the scaled domain $L \Lambda$ and denote the corresponding localised Fermi projection by $P_B(L\Lambda)$. Then we study the scaling of the Hilbert-space trace, $\mathrm{tr} f(P_B(L\Lambda))$, for polynomials $f$ with $f(0)=f(1)=0$ of these localised ground states in the joint limit $L\to\infty$ and $B\to0$. We obtain to leading order logarithmically enhanced area-laws depending on the size of $LB$. Roughly speaking, if $1/B$ tends to infinity faster than $L$, then we obtain the known enhanced area-law (by the Widom--Sobolev formula) of the form $L \ln(L) a(f,\mu) |\partial\Lambda|$ as $L\to\infty$ for the (two-dimensional) Laplacian with Fermi projection $1(H_0\le \mu)$. On the other hand, if $L$ tends to infinity faster than $1/B$, then we get an area law with an $L \ln(\mu/B) a(f,\mu) |\partial\Lambda|$ asymptotic expansion as $B\to0$. The numerical coefficient $a(f,\mu)$ in both cases is the same and depends solely on the function $f$ and on $\mu$. The asymptotic result in the latter case is based upon the recent joint work of Leschke, Sobolev and the second named author for fixed $B$, a proof of the sine-kernel asymptotics on a global scale, and on the enhanced area-law in dimension one by Landau and Widom. In the special but important case of a quadratic function $f$ we are able to cover the full range of parameters $B$ and $L$. In general, we have a smaller region of parameters $(B,L)$ where we can prove the two-scale asymptotic expansion $\mathrm{tr} f(P_B(L\Lambda))$ as $L\to\infty$ and $B\to0$.

Billiards with Spatial Memory. (arXiv:2307.01734v1 [nlin.CD])
Thijs Albers, Stijn Delnoij, Nico Schramma, Maziyar Jalaal

Many classes of active matter develop spatial memory by encoding information in space, leading to complex pattern formation. It has been proposed that spatial memory can lead to more efficient navigation and collective behaviour in biological systems and influence the fate of synthetic systems. This raises important questions about the fundamental properties of dynamical systems with spatial memory. We present a framework based on mathematical billiards in which particles remember their past trajectories and react to them. Despite the simplicity of its fundamental deterministic rules, such a system is strongly non-ergodic and exhibits highly-intermittent statistics, manifesting in complex pattern formation. We show how these self-memory-induced complexities emerge from the temporal change of topology and the consequent chaos in the system. We study the fundamental properties of these billiards and particularly the long-time behaviour when the particles are self-trapped in an arrested state. We exploit numerical simulations of several millions of particles to explore pattern formation and the corresponding statistics in polygonal billiards of different geometries. Our work illustrates how the dynamics of a single-body system can dramatically change when particles feature spatial memory and provide a scheme to further explore systems with complex memory kernels.

Spatial organization of slit-confined melts of ring polymers with non-conserved topology: A lattice Monte Carlo study. (arXiv:2307.01739v1 [cond-mat.soft])
Mattia Alberto Ubertini, Angelo Rosa

We present Monte Carlo computer simulations for melts of semiflexible randomly knotted and randomly concatenated ring polymers on the fcc lattice and in slit confinement. Through systematic variation of the slit width at fixed melt density, we first explore the influence of confinement on single-chain conformations and inter-chain interactions. We demonstrate that confinement makes chains globally larger and more elongated, while enhancing both contacts and knottedness propensities. As for multi-chain properties, we show that ring-ring contacts decrease with the confinement, yet neighbouring rings are more overlapped as confinement grows. These aspects are reflected on the decrease of the links formation between pairs of rings. The results suggest that confinement can be used to fine-tune the mechanical properties of the polymer network. In particular, confinement biases the synthesis of networks that are softer to mechanical stress. Finally, in connection with a previous study of us and recent simulations on two-dimensional polymer melts, our findings suggest that entanglements in polymer melts arise from pairwise ring-ring links alone.

A magnetically-induced Coulomb gap in graphene due to electron-electron interactions. (arXiv:2307.01757v1 [cond-mat.mes-hall])
E.E. Vdovin, M.T. Greenaway, Yu.N. Khanin, S.V. Morozov, O. Makarovsky, A. Patanè, A. Mishchenko, S. Slizovskiy, V.I. Fal'ko, A.K. Geim, K.S. Novoselov, L. Eaves

Insights into the fundamental properties of graphene's Dirac-Weyl fermions have emerged from studies of electron tunnelling transistors in which an atomically thin layer of hexagonal boron nitride (hBN) is sandwiched between two layers of high purity graphene. Here, we show that when a single defect is present within the hBN tunnel barrier, it can inject electrons into the graphene layers and its sharply defined energy level acts as a high resolution spectroscopic probe of electron-electron interactions in graphene. We report a magnetic field dependent suppression of the tunnel current flowing through a single defect below temperatures of $\sim$ 2 K. This is attributed to the formation of a magnetically-induced Coulomb gap in the spectral density of electrons tunnelling into graphene due to electron-electron interactions.

Properties of aqueous electrolyte solutions at carbon electrodes: effects of concentration and surface charge on solution structure, ion clustering and thermodynamics in the electric double layer. (arXiv:2307.01758v1 [cond-mat.soft])
Aaron R. Finney, Matteo Salvalaglio

Surfaces are able to control physical-chemical processes in multi-component solution systems and, as such, find application in a wide range of technological devices. Understanding the structure, dynamics and thermodynamics of non-ideal solutions at surfaces, however, is particularly challenging. Here, we use Constant Chemical Potential Molecular Dynamics simulations to gather insight into aqueous NaCl solutions in contact with graphite surfaces at high concentrations and under the effect of applied surface charges: conditions where mean-field theories describing interfaces cannot be (typically) reliably applied. We discover an asymmetric effect of surface charge on the double layer structure and resulting thermodynamic properties, which can be explained by considering the affinity of the surface for cations and anions and the cooperative adsorption of ions that occurs at higher concentrations. We characterise how the sign of the surface charge affects ion densities and water structure in the double layer and how the capacitance of the interface - a function of the electric potential drop across the double layer - is largely insensitive to the bulk solution concentration. Notably, we find that negatively charged graphite surfaces induce an increase in the size and concentration of extended liquid-like ion clusters confined to the double layer. Finally, we discuss how concentration and surface charge affect the activity coefficients of ions and water in the double layer, demonstrating how electric fields in this region should be explicitly considered when characterising the thermodynamics of both solute and solvent at the solid/liquid interface.

Boundary Flat Bands with Topological Spin Textures Protected by Sub-chiral Symmetry. (arXiv:2307.01851v1 [cond-mat.mtrl-sci])
Yijie Mo, Xiao-Jiao Wang, Rui Yu, Zhongbo Yan

Chiral symmetry plays an indispensable role in topological classifications as well as in the understanding of the origin of bulk or boundary flat bands. The conventional definition of chiral symmetry refers to the existence of a constant unitary matrix anticommuting with the Hamiltonian. As a constant unitary matrix has constant eigenvectors, boundary flat bands enforced by chiral symmetry, which share the same eigenvectors with the chiral symmetry operator, are known to carry fixed (pseudo)spin polarizations and be featureless in quantum geometry. In this work, we generalize the chiral symmetry and introduce a concept termed sub-chiral symmetry. Unlike the conventional chiral symmetry operator defined as constant, the sub-chiral symmetry operator depends on partial components of the momentum vector, so as its eigenvectors. We show that topological gapped or gapless systems without the chiral symmetry but with the sub-chiral symmetry can support boundary flat bands, which exhibit topological spin textures and quantized Berry phases. We expect that such intriguing boundary flat bands could give rise to a variety of exotic physics in the presence of interactions or disorders.

From Edge State Physics to Entanglement Spectrum: Studying Interactions and Impurities in Two-Dimensional Topological Insulators. (arXiv:2307.01913v1 [cond-mat.mes-hall])
Marcela Derli, E. Novais

We present a novel theoretical approach to incorporate electronic interactions in the study of two-dimensional topological insulators. By exploiting the correspondence between edge state physics and entanglement spectrum in gapped topological systems, we deconstruct the system into one-dimensional channels. This framework enables a simple and elegant inclusion of fermionic interactions into the discussion of topological insulators. We apply this approach to the Kane-Mele model with interactions and magnetic impurities.

Fragile superconductivity in a Dirac metal. (arXiv:2307.01976v1 [cond-mat.supr-con])
Chris J. Lygouras, Junyi Zhang, Jonah Gautreau, Mathew Pula, Sudarshan Sharma, Shiyuan Gao, Tanya Berry, Thomas Halloran, Peter Orban, Gael Grissonnanche, Juan R. Chamorro, Kagetora Mikuri, Dilip K. Bhoi, Maxime A. Siegler, Kenneth K. Livi, Yoshiya Uwatoko, Satoru Nakatsuji, B. J. Ramshaw, Yi Li, Graeme M. Luke, Collin L. Broholm, Tyrel M. McQueen

Studying superconductivity in Dirac semimetals is an important step in understanding quantum matter with topologically non-trivial order parameters. We report on the properties of the superconducting phase in single crystals of the Dirac material LaCuSb2 prepared by the self-flux method. We find that chemical and hydrostatic pressure drastically suppress the superconducting transition. Furthermore, due to large Fermi surface anisotropy, magnetization and muon spin relaxation measurements reveal Type-II superconductivity for applied magnetic fields along the $a$-axis, and Type-I superconductivity for fields along the $c$-axis. Specific heat confirms the bulk nature of the transition, and its deviation from single-gap $s$-wave BCS theory suggests multigap superconductivity. Our tight-binding model points to an anisotropic gap function arising from the spin-orbital texture near the Dirac nodes, providing an explanation for the appearance of an anomaly in specific heat well below $T_c$. Given the existence of superconductivity in a material harboring Dirac fermions, LaCuSb2 proves an interesting material candidate in the search for topological superconductivity.

Discovery of the high-entropy carbide ceramic topological superconductor candidate (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C. (arXiv:2307.02020v1 [cond-mat.supr-con])
Lingyong Zeng, Zequan Wang, Jing Song, Gaoting Lin, Ruixin Guo, Si-Chun Luo, Shu Guo, Kuan Li, Peifei Yu, Chao Zhang, Wei-Ming Guo, Jie Ma, Yusheng Hou, Huixia Luo

High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements. Material design and property tailoring possibilities emerge from this new class of materials. Here, we report the discovery of superconductivity around 2.35 K and topological properties in the (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C high-entropy carbide ceramic (HECC), which has not been observed before in any of the investigated HECC. Density functional theory calculations showed that six type-II Dirac points exist in (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)C, which mainly contributed from the t2g orbitals of transition metals and the p orbitals of C. Due to the stability of the structure, we also observed robust superconductivity under pressure in this HEC superconductor. This study expands the physical properties of HECs, which may become a new material platform for superconductivity research, especially for studying the coupling between superconductivity and topological physics.

Glass-like thermal conductivity and narrow insulating gap of EuTiO$_3$. (arXiv:2307.02058v1 [cond-mat.mtrl-sci])
Alexandre Jaoui, Shan Jiang, Xiaokang Li, Yasuhide Tomioka, Isao H. Inoue, Johannes Engelmayer, Rohit Sharma, Lara Pätzold, Thomas Lorenz, Benoît Fauqué, Kamran Behnia

Crystals and glasses differ by the amplitude and the temperature dependence of their thermal conductivity. However, there are crystals known to display glass-like thermal conductivity. Here, we show that EuTiO$_3$, a quantum paraelectric known to order antiferromagnetically at 5.5 K, is one such system. The temperature dependence of resistivity and Seebeck coefficient yield an insulating band gap of $\sim 0.22$ eV. Thermal conductivity is drastically reduced. Its amplitude and temperature dependence are akin to what is seen in amorphous silica. Comparison with non-magnetic perovskite solids, SrTiO$_3$, KTaO$_3$, and EuCoO$_3$, shows that what impedes heat transport are $4f$ spins at Eu$^{2+}$ sites, which couple to phonons well above the ordering temperature. Thus, in this case, superexchange and valence fluctuations, not magnetic frustration, are the drivers of the glass-like thermal conductivity.

Reflectionless pseudospin-1 Dirac systems via Darboux transformation and flat band solutions. (arXiv:2307.02123v1 [quant-ph])
Vit Jakubsky, Kevin Zelaya

This manuscript explores the Darboux transformation employed in the construction of exactly solvable models for pseudospin-one particles described by the Dirac-type equation. We focus on the settings where a flat band of zero energy is present in the spectrum of the initial system. Using the flat band state as one of the seed solutions substantially improves the applicability of the Darboux transformation, for it becomes necessary to ensure the Hermiticy of the new Hamiltonians. This is illustrated explicitly in four examples, where we show that the new Hamiltonians can describe quasi-particles in Lieb lattice with inhomogeneous hopping amplitudes.

Electric Polarization from Many-Body Neural Network Ansatz. (arXiv:2307.02212v1 [physics.chem-ph])
Xiang Li, Yubing Qian, Ji Chen

Ab initio calculation of dielectric response with high-accuracy electronic structure methods is a long-standing problem, for which mean-field approaches are widely used and electron correlations are mostly treated via approximated functionals. Here we employ a neural network wavefunction ansatz combined with quantum Monte Carlo to incorporate correlations into polarization calculations. On a variety of systems, including isolated atoms, one-dimensional chains, two-dimensional slabs, and three-dimensional cubes, the calculated results outperform conventional density functional theory and are consistent with the most accurate calculations and experimental data. Furthermore, we have studied the out-of-plane dielectric constant of bilayer graphene using our method and re-established its thickness dependence. Overall, this approach provides a powerful tool to consider electron correlation in the modern theory of polarization.

Equivariant graph neural network interatomic potential for Green-Kubo thermal conductivity in phase change materials. (arXiv:2307.02327v1 [cond-mat.mtrl-sci])
Sung-Ho Lee, Jing Li, Valerio Olevano, Benoit Sklénard

Thermal conductivity is a fundamental material property that plays an essential role in technology, but its accurate evaluation presents a challenge for theory. In this letter, we demonstrate the application of E(3)-equivariant neutral network interatomic potentials within Green-Kubo formalism to determine the lattice thermal conductivity in amorphous and crystalline materials. We apply this method to study the thermal conductivity of germanium telluride (GeTe) as a prototypical phase change material. A single deep learning interatomic potential is able to describe the phase transitions between the amorphous, rhombohedral and cubic phases, with critical temperatures in good agreement with experiments. Furthermore, this approach accurately captures the pronounced anharmonicity present in GeTe, enabling precise calculations of thermal conductivity. In contrast, the Boltzmann transport equation tends to overestimate it by approximately a factor of two in the crystalline phases.

Necessary and sufficient symmetries in Event-Chain Monte Carlo with generalized flows and Application to hard dimers. (arXiv:2307.02341v1 [cond-mat.stat-mech])
Tristan Guyon, Arnaud Guillin, Manon Michel

Event-Chain Monte Carlo methods generate continuous-time and non-reversible Markov processes which often display important accelerations compared to their reversible counterparts. However their generalization to any system may appear less straightforward. In this work, we build on the recent analytical characterization of such methods as generating Piecewise Deterministic Markov Processes (PDMP) to clearly decipher the necessary symmetries the PDMP must obey from the sufficient ones which may prove to be too restrictive in a general setting. Thus, we derive a necessary rotational invariance of the probability flows and the minimum event rate, which identifies with the corresponding infinitesimal rejection rate. Such conditions always yield a correct ECMC scheme. We then generalize such results to the case of more general deterministic flows than the translational ones. In particular, we define two classes of interest of general flows, the ideal and uniform-ideal ones, which respectively suppresses or reduces the event rates. From there, we implement a complete non-reversible sampling of a systems of hard dimers, thanks to the introduction of rotational flows, which are uniform-ideal and shows a speed-up of up to ~3 compared to the state-of-the-art ECMC/Metropolis hybrid scheme.

Visible-Light Assisted Covalent Surface Functionalization of Reduced Graphene Oxide Nanosheets with Arylazo Sulfones. (arXiv:2307.02353v1 [cond-mat.mes-hall])
Lorenzo Lombardi, Alessandro Kovtun, Sebastiano Mantovani, Giulio Bertuzzi, Laura Favaretto, Cristian Bettini, Vincenzo Palermo, Manuela Melucci, Marco Bandini

We present an environmentally benign methodology for the covalent functionalization (arylation) of reduced graphene oxide (rGO) nanosheets with arylazo sulfones. A variety of tagged aryl units were conveniently accommodated at the rGO surface via visible light irradiation of suspensions of carbon nanostructured materials in aqueous media. Mild reaction conditions, absence of photosensitizers, functional group tolerance and high atomic fractions (XPS analysis) represent some of the salient features characterizing the present methodology. Control experiments for the mechanistic elucidation (Raman analysis) and chemical nanomanipulation of the tagged rGO surfaces are also reported.

Quantum Fisher Information and multipartite entanglement in spin-1 chains. (arXiv:2307.02407v1 [quant-ph])
Federico Dell'Anna, Sunny Pradhan, Cristian Degli Esposti Boschi, Elisa Ercolessi

In this paper, we study the ground state Quantum Fisher Information (QFI) in one-dimensional spin-1 models, as witness to Multipartite Entanglement. The models addressed are the Bilinear-Biquadratic model, the most general isotropic SU(2)-invariant spin-1 chain, and the XXZ spin-1 chain, both with nearest-neighbor interactions and open boundary conditions. We show that the scaling of the QFI of strictly non-local observables can be used for characterizing the phase diagrams and, in particular, for studying topological phases, where it scales maximally. Analysing its behavior at the critical phases we are also able to recover the scaling dimensions of the order parameters both for local and string observables. The numerical results have been obtained by exploiting the Density Matrix Renormalization Group algorithm and Tensor Network techniques.

Optimization on manifolds: A symplectic approach. (arXiv:2107.11231v2 [cond-mat.stat-mech] UPDATED)
Guilherme França, Alessandro Barp, Mark Girolami, Michael I. Jordan

Optimization tasks are crucial in statistical machine learning. Recently, there has been great interest in leveraging tools from dynamical systems to derive accelerated and robust optimization methods via suitable discretizations of continuous-time systems. However, these ideas have mostly been limited to Euclidean spaces and unconstrained settings, or to Riemannian gradient flows. In this work, we propose a dissipative extension of Dirac's theory of constrained Hamiltonian systems as a general framework for solving optimization problems over smooth manifolds, including problems with nonlinear constraints. We develop geometric/symplectic numerical integrators on manifolds that are "rate-matching," i.e., preserve the continuous-time rates of convergence. In particular, we introduce a dissipative RATTLE integrator able to achieve optimal convergence rate locally. Our class of (accelerated) algorithms are not only simple and efficient but also applicable to a broad range of contexts.

Molecular Beam Epitaxy growth of MoTe$_2$ on Hexagonal Boron Nitride. (arXiv:2111.12433v4 [cond-mat.mtrl-sci] UPDATED)
Bartłomiej Seredyński, Rafał Bożek, Jan Suffczyński, Justyna Piwowar, Janusz Sadowski, Wojciech Pacuski

Hexagonal boron nitride has already been proven to serve as a decent substrate for high quality epitaxial growth of several 2D materials, such as graphene, MoSe$_{\tiny{\textrm{2}}}$, MoS$_{\tiny{\textrm{2}}}$ or WSe$_{\tiny{\textrm{2}}}$. Here, we present for the first time the molecular beam epitaxy growth of MoTe$_{\tiny{\textrm{2}}}$ on atomically smooth hexagonal boron nitride (hBN) substrate. Occurrence of MoTe$_{\tiny{\textrm{2}}}$ in various crystalline phases such as distorted octahedral 1T' phase with semimetal properties or hexagonal 2H phase with semiconducting properties opens a possibility of realisation of crystal-phase homostructures with tunable properties. Atomic force microscopy studies of MoTe$_{\tiny{\textrm{2}}}$ grown in a single monolayer regime enable us to determine surface morphology as a function of the growth conditions. The diffusion constant of MoTe$_{\tiny{\textrm{2}}}$ grown on hBN can be altered 5 times by annealing after the growth, reaching about 5 $\cdot$ 10$^{-6}$ cm$^{2}$/s. Raman spectroscopy results suggest a coexistence of both 2H and 1T' MoTe$_{\tiny{\textrm{2}}}$ phases in the studied samples.

Locality and error correction in quantum dynamics with measurement. (arXiv:2206.09929v4 [quant-ph] UPDATED)
Aaron J. Friedman, Chao Yin, Yifan Hong, Andrew Lucas

The speed of light $c$ sets a strict upper bound on the speed of information transfer in both classical and quantum systems. In nonrelativistic quantum systems, the Lieb-Robinson Theorem imposes an emergent speed limit $v \hspace{-0.2mm} \ll \hspace{-0.2mm} c$, establishing locality under unitary evolution and constraining the time needed to perform useful quantum tasks. We extend the Lieb-Robinson Theorem to quantum dynamics with measurements. In contrast to the expectation that measurements can arbitrarily violate spatial locality, we find at most an $(M \hspace{-0.5mm} +\hspace{-0.5mm} 1)$-fold enhancement to the speed $v$ of quantum information, provided the outcomes of measurements in $M$ local regions are known. This holds even when classical communication is instantaneous, and extends beyond projective measurements to weak measurements and other nonunitary channels. Our bound is asymptotically optimal, and saturated by existing measurement-based protocols. We tightly constrain the resource requirements for quantum computation, error correction, teleportation, and generating entangled resource states (Bell, GHZ, quantum-critical, Dicke, W, and spin-squeezed states) from short-range-entangled initial states. Our results impose limits on the use of measurements and active feedback to speed up quantum information processing, resolve fundamental questions about the nature of measurements in quantum dynamics, and constrain the scalability of a wide range of proposed quantum technologies.

Two-dimensional non-linear hydrodynamics and nanofluidics. (arXiv:2207.02870v2 [cond-mat.mtrl-sci] UPDATED)
Maxim Trushin, Alexandra Carvalho, A. H. Castro Neto

A water monolayer squeezed between two solid planes experiences strong out-of-plane confinement effects while expanding freely within the plane. As a consequence, the transport of such two-dimensional water combines hydrodynamic and nanofluidic features, intimately linked with each other. In this paper, we propose and explicitly solve a non-linear hydrodynamic equation describing two-dimensional water flow with viscosity parameters deduced from molecular dynamic simulations. We demonstrate that the very ability of two-dimensional water to flow in short channels is governed by the second (dilatational) viscosity coefficient, leading to flow compression and velocity saturation in the high-pressure limit. The viscosity parameter values depend strongly on whether graphene or hexoganal boron nitride layers are used to confine 2D water that offers an interesting opportunity to obtain various nanofluids out of the same water molecules just by using alternate materials to fabricate the 2D channels.

Non-degenerate surface pair density wave in the Kagome superconductor CsV$_3$Sb$_5$ -- application to vestigial orders. (arXiv:2210.00023v3 [cond-mat.supr-con] UPDATED)
Yue Yu

On the Sb-layer of the Kagome superconductor CsV$_3$Sb$_5$, pair density wave states have been observed. When the high-temperature charge orderings are treated as static backgrounds, these PDW states exhibit the same wavevector in the effective 2D Brillouin zone. Interestingly, these PDW states break the same symmetry on the surface. Considering the presence of this non-degenerate PDW, we investigate the implications for the possible existence of a vestigial charge-4e phase with a non-zero center-of-mass momentum. To distinguish between different vestigial phases, we propose scanning tunneling microscopy experiments. We aim to provide insights into the nature of the vestigial phases and their distinct characteristics in CsV$_3$Sb$_5$. This research sheds light on the interplay between PDW states, charge orderings, and superconductivity of the Kagome superconductor.

Solitonic symmetry beyond homotopy: Invertibility from bordism and noninvertibility from topological quantum field theory. (arXiv:2210.13780v4 [hep-th] UPDATED)
Shi Chen, Yuya Tanizaki

Solitonic symmetry has been believed to follow the homotopy-group classification of topological solitons. Here, we point out a more sophisticated algebraic structure when solitons of different dimensions coexist in the spectrum. We uncover this phenomenon in a concrete quantum field theory, the $4$d $\mathbb{C}P^1$ model. This model has two kinds of solitonic excitations, vortices and hopfions, which would follow two $U(1)$ solitonic symmetries according to homotopy groups. Nevertheless, we demonstrate the nonexistence of the hopfion $U(1)$ symmetry by evaluating the hopfion charge of vortex operators. We clarify that what conserves hopfion numbers is a non-invertible symmetry generated by 3d spin topological quantum field theories (TQFTs). Its invertible part is just $\mathbb{Z}_2$, which we recognize as a spin bordism invariant. Compared with the 3d $\mathbb{C}P^1$ model, our work suggests a unified description of solitonic symmetries and couplings to topological phases.

Magnetization Dynamics in Synthetic Antiferromagnets with Perpendicular Magnetic Anisotropy. (arXiv:2211.07744v2 [cond-mat.mes-hall] UPDATED)
Dingbin Huang, Delin Zhang, Yun Kim, Jian-Ping Wang, Xiaojia Wang

Understanding the rich physics of magnetization dynamics in perpendicular synthetic antiferromagnets (p-SAFs) is crucial for developing next-generation spintronic devices. In this work, we systematically investigate the magnetization dynamics in p-SAFs combining time-resolved magneto-optical Kerr effect (TR-MOKE) measurements with theoretical modeling. These model analyses, based on a Landau-Lifshitz-Gilbert approach incorporating exchange coupling, provide details about the magnetization dynamic characteristics including the amplitudes, directions, and phases of the precession of p-SAFs under varying magnetic fields. These model-predicted characteristics are in excellent quantitative agreement with TR-MOKE measurements on an asymmetric p-SAF. We further reveal the damping mechanisms of two procession modes co-existing in the p-SAF and successfully identify individual contributions from different sources, including Gilbert damping of each ferromagnetic layer, spin pumping, and inhomogeneous broadening. Such a comprehensive understanding of magnetization dynamics in p-SAFs, obtained by integrating high-fidelity TR-MOKE measurements and theoretical modeling, can guide the design of p-SAF-based architectures for spintronic applications.

Fermionic defects of topological phases and logical gates. (arXiv:2211.12394v2 [cond-mat.str-el] UPDATED)
Ryohei Kobayashi

We discuss the codimension-1 defects of (2+1)D bosonic topological phases, where the defects can support fermionic degrees of freedom. We refer to such defects as fermionic defects, and introduce a certain subclass of invertible fermionic defects called "gauged Gu-Wen SPT defects" that can shift self-statistics of anyons. We derive a canonical form of a general fermionic invertible defect, in terms of the fusion of a gauged Gu-Wen SPT defect and a bosonic invertible defect decoupled from fermions on the defect. We then derive the fusion rule of generic invertible fermionic defects. The gauged Gu-Wen SPT defects give rise to interesting logical gates of stabilizer codes in the presence of additional ancilla fermions. For example, we find a realization of the CZ logical gate on the (2+1)D $\mathbb{Z}_2$ toric code stacked with a (2+1)D ancilla trivial atomic insulator, which is implemented by a finite depth circuit. We also investigate a gapped fermionic interface between (2+1)D bosonic topological phases realized on the boundary of the (3+1)D Walker-Wang model. In that case, the gapped interface can shift the chiral central charge of the (2+1)D phase. Among these fermionic interfaces, we study an interesting example where the (3+1)D phase has a spatial reflection symmetry, and the fermionic interface is supported on a reflection plane that interpolates a (2+1)D surface topological order and its orientation-reversal. We construct a (3+1)D exactly solvable Hamiltonian realizing this setup, and find that the model generates the $\mathbb{Z}_8$ classification of the (3+1)D invertible phase with spatial reflection symmetry and fermion parity on the reflection plane. We make contact with an effective field theory, known in literature as the exotic invertible phase with spacetime higher-group symmetry.

Kagome chiral spin liquid in transition metal dichalcogenide moir\'e bilayers. (arXiv:2211.15696v2 [cond-mat.str-el] UPDATED)
Johannes Motruk, Dario Rossi, Dmitry A. Abanin, Louk Rademaker

At $n=3/4$ filling of the moir\'e flat band, transition metal dichalcogenide moir\'e bilayers will develop kagome charge order. We derive an effective spin model for the resulting localized spins and find that its further neighbor spin interactions can be much less suppressed than the corresponding electron hopping strength. Using density matrix renormalization group simulations, we study its phase diagram and, for realistic model parameters relevant for WSe$_2$/WS$_2$, we show that this material can realize the exotic chiral spin liquid phase and the highly debated kagome spin liquid. Our work thus demonstrates that the frustration and strong interactions present in TMD heterobilayers provide an exciting platform to study spin liquid physics.

Weyl Metal Phase in Delafossite Oxide PtNiO$_2$. (arXiv:2212.00579v2 [cond-mat.mtrl-sci] UPDATED)
Gang Bahadur Acharya, Mohan Bikram Neupane, Rojila Ghimire, Madhav Prasad Ghimire

On the basis of density functional theory calculations we predict Weyl points in rhombohedral structure of PtNiO$_2$ having symmorphic symmetry. From the formation energy and phonon calculations, PtNiO$_2$ is found to be structurally stable. The magnetic ground state is ferromagnetic with an effective magnetic moment of 1.01 $\mu_B$ per unit cell. The electronic structure shows major contributions from Pt-$5d$, Ni-$3d$ and O-$2p$ orbitals with band crossing close to the Fermi level. The orbital contribution around 8 eV above the Fermi level are from the Pt-$s,p$ orbitals forming a kagome like electronic structure confirmed by surface Fermi surface spectral function. We found 20 pairs of confirmed Weyl nodes along the magnetic easy axis [100]. These results are expected to provide a useful and exciting platform for exploring and understanding the magnetic Weyl physics in delafossites.

Quadrupole partial orders and triple-$q$ states on the face-centered cubic lattice. (arXiv:2212.12920v2 [cond-mat.str-el] UPDATED)
Kazumasa Hattori, Takayuki Ishitobi, Hirokazu Tsunetsugu

We study $\Gamma_3$ quadrupole orders in a face-centered cubic lattice. The $\Gamma_3$ quadrupole moments under cubic symmetry possess a unique cubic invariant in their free energy in the uniform ($q=0$) sector and the triple-q sector for the X points $q=(2\pi,0,0),(0,2\pi,0)$, and $(0,0,2\pi)$. Competition between this cubic anisotropy and anisotropic quadrupole-quadrupole interactions causes a drastic impact on the phase diagram both in the ground state and at finite temperatures. We show details about the model construction and its properties, the phase diagram, and the mechanism of the various triple-$q$ quadrupole orders reported in our preceding letter [J. Phys. Soc. Jpn. 90, 43701 (2021), arXiv:2102.06346]. By using a mean-field approach, we analyze a quadrupole exchange model that consists of a crystalline-electric field scheme with the ground-state $\Gamma_3$ non-Kramers doublet and the excited singlet $\Gamma_1$ state. We find various triple-$q$ orders in the four-sublattice mean-field approximation. A few partial orders of quadrupoles are stabilized in a wide range of parameter space at a higher transition temperature than single-$q$ orders. With lowering the temperature, these partial orders undergo phase transitions into further symmetry broken phases in which nonvanishing quadrupole moments emerge at previously disordered sites. The obtained phases in the mean-field approximation are investigated by a phenomenological Landau theory, which clearly shows that the cubic invariant plays an important role for stabilizing the triple-$q$ states. We also discuss its implications for recent experiments in a few f- and d-electron compounds.

Electronic structure of biased alternating-twist multilayer graphene. (arXiv:2212.14541v2 [cond-mat.mes-hall] UPDATED)
Kyungjin Shin, Yunsu Jang, Jiseon Shin, Jeil Jung, Hongki Min

We theoretically study the energy and optical absorption spectra of alternating twist multilayer graphene (ATMG) under a perpendicular electric field. We obtain analytically the low-energy effective Hamiltonian of ATMG up to pentalayer in the presence of the interlayer bias by means of first-order degenerate-state perturbation theory, and present general rules for constructing the effective Hamiltonian for an arbitrary number of layers. Our analytical results agree to an excellent degree of accuracy with the numerical calculations for twist angles $\theta \gtrsim 2.2^{\circ}$ that are larger than the typical range of magic angles. We also calculate the optical conductivity of ATMG and determine its characteristic optical spectrum, which is tunable by the interlayer bias. When the interlayer potential difference is applied between consecutive layers of ATMG, the Dirac cones at the two moir\'{e} Brillouin zone corners $\bar{K}$ and $\bar{K}'$ acquire different Fermi velocities, generally smaller than that of monolayer graphene, and the cones split proportionally in energy resulting in a step-like feature in the optical conductivity.

Advanced magnon-optic effects with spin-wave leaky modes. (arXiv:2302.11507v3 [cond-mat.mes-hall] UPDATED)
Krzysztof Sobucki, Wojciech Śmigaj, Piotr Graczyk, Maciej Krawczyk, and Paweł Gruszecki

We numerically demonstrate the excitation of leaky spin waves (SWs) guided along a ferromagnetic stripe by an obliquely incident SW beam on the thin film edge placed below the stripe. During propagation, leaky waves emit energy back to the layer in the form of plane waves and several laterally shifted parallel SW beams. This resonance excitation, combined with interference effects of the reflected and re-emitted waves, results in the magnonic Woods anomaly and significant increase of the Goos-Hanchen shift magnitude. Hence, we provide a unique platform to control SW reflection and to transfer SWs from a 2D platform into the 1D guiding mode that can be used to form a transdimensional magnonic router.

Finite-temperature phase transitions in $S=1/2$ three-dimensional Heisenberg magnets from high-temperature series expansions. (arXiv:2303.03135v3 [cond-mat.str-el] UPDATED)
M. G. Gonzalez, B. Bernu, L. Pierre, L. Messio

Many frustrated spin models on three-dimensional (3D) lattices are currently being investigated, both experimentally and theoretically, and develop new types of long-range orders in their respective phase diagrams. They present finite-temperature phase transitions, most likely in the Heisenberg 3D universality class. However, the combination between the 3D character and frustration makes them hard to study. We present here several methods derived from high-temperature series expansions (HTSEs), which give exact coefficients directly in the thermodynamic limit up to a certain order; for several 3D lattices, supplementary orders than in previous literature are reported for the HTSEs. We introduce an interpolation method able to describe thermodynamic quantities at $T > T_c$, which we use here to reconstruct the magnetic susceptibility and the specific heat and to extract universal and non-universal quantities (for example critical exponents, temperature, energy, entropy, and other parameters related to the phase transition). While the susceptibility associated with the order parameter is not usually known for more exotic long-range orders, the specific heat is indicative of a phase transition for any kind of symmetry breaking. We present examples of applications on ferromagnetic and antiferromagnetic models on various 3D lattices and benchmark our results whenever possible.

Extracting higher central charge from a single wave function. (arXiv:2303.04822v3 [cond-mat.str-el] UPDATED)
Ryohei Kobayashi, Taige Wang, Tomohiro Soejima, Roger S. K. Mong, Shinsei Ryu

A (2+1)D topologically ordered phase may or may not have a gappable edge, even if its chiral central charge $c_-$ is vanishing. Recently, it is discovered that a quantity regarded as a ``higher'' version of chiral central charge gives a further obstruction beyond $c_-$ to gapping out the edge. In this Letter, we show that the higher central charges can be characterized by the expectation value of the \textit{partial rotation} operator acting on the wavefunction of the topologically ordered state. This allows us to extract the higher central charge from a single wavefunction, which can be evaluated on a quantum computer. Our characterization of the higher central charge is analytically derived from the modular properties of edge conformal field theory, as well as the numerical results with the $\nu=1/2$ bosonic Laughlin state and the non-Abelian gapped phase of the Kitaev honeycomb model, which corresponds to $\mathrm{U}(1)_2$ and Ising topological order respectively. The letter establishes a numerical method to obtain a set of obstructions to the gappable edge of (2+1)D bosonic topological order beyond $c_-$, which enables us to completely determine if a (2+1)D bosonic Abelian topological order has a gappable edge or not. We also point out that the expectation values of the partial rotation on a single wavefunction put a constraint on the low-energy spectrum of the bulk-boundary system of (2+1)D bosonic topological order, reminiscent of the Lieb-Schultz-Mattis type theorems.

Projectability disentanglement for accurate and automated electronic-structure Hamiltonians. (arXiv:2303.07877v2 [physics.comp-ph] UPDATED)
Junfeng Qiao, Giovanni Pizzi, Nicola Marzari

Maximally-localized Wannier functions (MLWFs) are a powerful and broadly used tool to characterize the electronic structure of materials, from chemical bonding to dielectric response to topological properties. Most generally, one can construct MLWFs that describe isolated band manifolds, e.g. for the valence bands of insulators, or entangled band manifolds, e.g. in metals or describing both the valence and the conduction manifolds in insulators. Obtaining MLWFs that describe a target manifold accurately and with the most compact representation often requires chemical intuition and trial and error, a challenging step even for experienced researchers and a roadblock for automated high-throughput calculations. Here, we present a powerful approach that automatically provides MLWFs spanning the occupied bands and their natural complement for the empty states, resulting in Wannier Hamiltonian models that provide a tight-binding picture of optimized atomic orbitals in crystals. Key to the success of the algorithm is the introduction of a projectability measure for each Bloch state onto atomic orbitals (here, chosen from the pseudopotential projectors) that determines if that state should be kept identically, discarded, or mixed into a disentangling algorithm. We showcase the accuracy of our method by comparing a reference test set of 200 materials against the selected-columns-of-the-density-matrix algorithm, and its reliability by constructing Wannier Hamiltonians for 21737 materials from the Materials Cloud.

Stationary Two-State System in Optics using Layered Materials. (arXiv:2303.08395v2 [quant-ph] UPDATED)
Ken-ichi Sasaki

When electrodynamics is quantized in a situation where the electrons exist only at a flat surface such as graphene, one of the Maxwell equations appears as a local part of the Hamiltonian. As a consequence of gauge invariance, any physical state has to be a zero-energy state of the local Hamiltonian. We construct two stationary quantum states; one reproduces scattering and absorption of light, which is familiar in classical optics and the other is more fundamentally related to photon creation. These two states are inseparable by the Hamiltonian and forming a two-state system, but there is a special number of surfaces for which two states are decoupled. The number is $2/\pi \alpha$ where $\pi \alpha$ is the absorption probability of single surface.

Hyperfine interactions in open-shell planar $sp^2$-carbon nanostructures. (arXiv:2303.11422v2 [cond-mat.mes-hall] UPDATED)
Sanghita Sengupta, Thomas Frederiksen, Geza Giedke

We investigate hyperfine interaction (HFI) using density-functional theory for several open-shell planar $sp^2$-carbon nanostructures displaying $\pi$ magnetism. Our prototype structures include both benzenoid ([$n$]triangulenes and a graphene nanoribbon) as well as non-benzenoid (indene, fluorene, and indene[2,1-b]fluorene) molecules. Our results obtained with ORCA indicate that isotropic Fermi contact and anisotropic dipolar terms contribute in comparable strength, rendering the HFI markedly anisotropic. We find that the magnitude of HFI in these molecules can reach more than 100 MHz, thereby opening up the possibility of experimental detection via methods such as electron spin resonance-scanning tunneling microscopy (ESR-STM). Using these results, we obtain empirical models based on $\pi$-spin polarizations at carbon sites. These are defined by generic $sp^{2}$ HFI fit parameters which are derived by matching the computed HFI couplings to $\pi$-spin polarizations computed with methods such as ORCA, SIESTA, or mean-field Hubbard (MFH) models. This approach successfully describes the Fermi contact and dipolar contributions for $^{13}$C and $^{1}$H nuclei. These fit parameters allow to obtain hyperfine tensors for large systems where existing methodology is not suitable or computationally too expensive. As an example, we show how HFI scales with system size in [$n$]triangulenes for large $n$ using MFH. We also discuss some implications of HFI for electron-spin decoherence and for coherent nuclear dynamics.

On the size of superconducting islands on the density-wave background in organic metals. (arXiv:2305.14510v2 [cond-mat.supr-con] UPDATED)
Vladislav D. Kochev, Seidali S. Seidov, Pavel D. Grigoriev

Most high-$T_c$ superconductors are spatially inhomogeneous. Usually, this heterogeneity originates from the interplay of various types of electronic ordering. It affects various superconducting properties, such as the transition temperature, the magnetic upper critical field, the critical current, etc. In this paper, we analyze the parameters of spatial phase segregation during the first-order transition between superconductivity (SC) and a charge- or spin-density wave state in quasi-one-dimensional metals with imperfect nesting, typical of organic superconductors. An external pressure or another driving parameter increases the transfer integrals in electron dispersion, which only slightly affects SC but violates the Fermi surface nesting and suppresses the density wave (DW). At a critical pressure $P_{c}$, the transition from a DW to SC occurs. We estimate the characteristic size of superconducting islands during this phase transition in organic metals in two ways. Using the Ginzburg-Landau expansion, we analytically obtain a lower bound for the size of SC domains. To estimate a more specific interval of the possible size of the superconducting islands in (TMTSF)$_2$PF$_6$ samples, we perform numerical calculations of the percolation probability via SC domains and compare the results with experimental resistivity data. This helps to develop a consistent microscopic description of SC spatial heterogeneity in various organic superconductors.

Symmetric Mass Generation of K\"ahler-Dirac Fermions from the Perspective of Symmetry-Protected Topological Phases. (arXiv:2306.17420v2 [cond-mat.str-el] UPDATED)
Yuxuan Guo, Yi-Zhuang You

The K\"ahler-Dirac fermion, recognized as an elegant geometric approach, offers an alternative to traditional representations of relativistic fermions. Recent studies have demonstrated that symmetric mass generation (SMG) can precisely occur with two copies of K\"ahler-Dirac fermions across any spacetime dimensions. This conclusion stems from the study of anomaly cancellation within the fermion system. Our research provides an alternative understanding of this phenomenon from a condensed matter perspective, by associating the interacting K\"ahler-Dirac fermion with the boundary of bosonic symmetry-protected topological (SPT) phases. We show that the low-energy bosonic fluctuations in a single copy of the K\"ahler-Dirac fermion can be mapped to the boundary modes of a $\mathbb{Z}_2$-classified bosonic SPT state, protected by an inversion symmetry universally across all dimensions. This implies that two copies of K\"ahler-Dirac fermions can always undergo SMG through interactions mediated by these bosonic modes. This picture aids in systematically designing SMG interactions for K\"ahler-Dirac fermions in any dimension. We present the exact lattice Hamiltonian of these interactions and validate their efficacy in driving SMG.

Found 18 papers in prb
Date of feed: Thu, 06 Jul 2023 03:17:07 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Meron configurations in easy-plane chiral magnets
David Bachmann, Michail Lianeris, and Stavros Komineas
Author(s): David Bachmann, Michail Lianeris, and Stavros Komineas

We demonstrate the existence and study in detail the features of chiral bimerons which are static solutions in an easy-plane magnet with the Dzyaloshinskii-Moriya interaction. These are skyrmionic textures with an integer topological charge, and they present essential analogies to the meron configur…

[Phys. Rev. B 108, 014402] Published Wed Jul 05, 2023

Van Roosbroeck's equations with topological terms: The case of Weyl semimetals
Pierre-Antoine Graham, Simon Bertrand, Michaël Bédard, Robin Durand, and Ion Garate
Author(s): Pierre-Antoine Graham, Simon Bertrand, Michaël Bédard, Robin Durand, and Ion Garate

For decades, van Roosbroeck’s (VR) equations have been used to model microelectronic devices made from ordinary semiconductors. The advent of topological materials raises a largely unexplored question: how are VR equations and their solutions modified when electronic bands are topological? Here, the authors solve VR equations analytically in a Weyl semimetal placed under a magnetic field and subjected to a spatially inhomogeneous light pulse. They predict photoinduced plasma oscillations, which originate from a topological term in VR equations.

[Phys. Rev. B 108, 024301] Published Wed Jul 05, 2023

Exploring terahertz-scale exchange resonances in synthetic ferrimagnets with ultrashort optically induced spin currents
Julian Hintermayr, Youri L. W. van Hees, and Bert Koopmans
Author(s): Julian Hintermayr, Youri L. W. van Hees, and Bert Koopmans

Using spin currents generated by fs laser pulses, we demonstrate excitation of GHz ferromagnetic resonance and THz ferrimagnetic exchange resonances in Co/Gd/Co/Gd multilayers by time-resolved magneto-optic Kerr effect measurements. Varying the Gd layer thickness allows for a tuning of the resonance…

[Phys. Rev. B 108, 024401] Published Wed Jul 05, 2023

Spin-current driven Dzyaloshinskii-Moriya interaction in multiferroic ${\mathrm{BiFeO}}_{3}$ from first principles
Sebastian Meyer, Bin Xu, Matthieu J. Verstraete, Laurent Bellaiche, and Bertrand Dupé
Author(s): Sebastian Meyer, Bin Xu, Matthieu J. Verstraete, Laurent Bellaiche, and Bertrand Dupé

The electrical control of magnons opens up new ways to transport and process information for logic devices. In magnetoelectrical multiferroics, the Dzyaloshinskii-Moriya (DM) interaction directly allows for such control and hence is of major importance. We determine the origin and the strength of th…

[Phys. Rev. B 108, 024403] Published Wed Jul 05, 2023

Dark Andreev states in superconductors
Andrey Grankin and Victor Galitski
Author(s): Andrey Grankin and Victor Galitski

The conventional Bardeen-Cooper-Schrieffer model of superconductivity assumes a frequency-independent order parameter, which allows a relatively simple description of the superconducting state. In particular, its excitation spectrum readily follows from the Bogoliubov–de Gennes (BdG) equations. A mo…

[Phys. Rev. B 108, 024501] Published Wed Jul 05, 2023

Interlayer electronic superfluid in an external magnetic field in graphene double layers
Andreas Sinner
Author(s): Andreas Sinner

We investigate the formation mechanism of the recently proposed interlayer electronic superfluid state due to repulsive interaction in graphene double layers. Using the renormalization group argumentation we show how the emergence of a particular interlayer staggered order parameter wins the competi…

[Phys. Rev. B 108, 024502] Published Wed Jul 05, 2023

Magnetic, electronic, and thermal properties of buckled kagome ${\mathrm{Fe}}_{3}{\mathrm{Ge}}_{2}\mathrm{Sb}$
Quinn D. Gibson, Ramzy Daou, Marco Zanella, Jonathan Alaria, and Matthew J. Rosseinsky
Author(s): Quinn D. Gibson, Ramzy Daou, Marco Zanella, Jonathan Alaria, and Matthew J. Rosseinsky

The magnetic, electronic, and thermal properties of ${\mathrm{Fe}}_{3}{\mathrm{Ge}}_{2}\mathrm{Sb}$ single crystals, a derivative of the hexagonal FeGe structure with a buckled Fe kagome net and Sb-Sb dimers are reported. Electronic structure calculations show most of the kagome-derived bands remain…

[Phys. Rev. B 108, 035102] Published Wed Jul 05, 2023

Slow diffusion and Thouless localization criterion in modulated spin chains
P. Prelovšek, J. Herbrych, and M. Mierzejewski
Author(s): P. Prelovšek, J. Herbrych, and M. Mierzejewski

In recent years the ergodicity of disordered spin chains has been investigated via extensive numerical studies of the level statistics or the transport properties. However, a clear relationship between these results has yet to be established. We present the relation between the diffusion constant an…

[Phys. Rev. B 108, 035106] Published Wed Jul 05, 2023

Mixed higher-order topology: Boundary non-Hermitian skin effect induced by a Floquet bulk
Hui Liu and Ion Cosma Fulga
Author(s): Hui Liu and Ion Cosma Fulga

We show that anomalous Floquet topological insulators generate intrinsic, non-Hermitian topology on their boundaries. As a consequence, removing a boundary hopping from the time-evolution operator stops the propagation of chiral edge modes, leading to a non-Hermitian skin effect. This does not occur…

[Phys. Rev. B 108, 035107] Published Wed Jul 05, 2023

Emergence of Rashba spin valley state in two-dimensional strained bismuth oxychalcogenides ${\mathrm{Bi}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$
Muhammad Darwis Umar, Lalu Dalilul Falihin, Arief Lukmantoro, Harsojo, and Moh. Adhib Ulil Absor
Author(s): Muhammad Darwis Umar, Lalu Dalilul Falihin, Arief Lukmantoro, Harsojo, and Moh. Adhib Ulil Absor

The experimental evidence of the ultrahigh electron mobility and strong spin-orbit coupling in the two-dimensional (2D) layered bismuth-based oxyselenide, ${\mathrm{Bi}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$, makes it a potential material for spintronic devices. However, its spin-related properties have n…

[Phys. Rev. B 108, 035109] Published Wed Jul 05, 2023

Topologically nontrivial and trivial zero modes in chiral molecules
Xiao-Feng Chen, Wenchen Luo, Tie-Feng Fang, Yossi Paltiel, Oded Millo, Ai-Min Guo, and Qing-Feng Sun
Author(s): Xiao-Feng Chen, Wenchen Luo, Tie-Feng Fang, Yossi Paltiel, Oded Millo, Ai-Min Guo, and Qing-Feng Sun

Recently, electron transport along chiral molecules has been attracting extensive interest and a number of intriguing phenomena have been reported in recent experiments, such as the emergence of zero-bias conductance peaks in the transmission spectrum upon the adsorption of single-helical protein on…

[Phys. Rev. B 108, 035401] Published Wed Jul 05, 2023

Universal control of superexchange in linear triple quantum dots with an empty mediator
Guo Xuan Chan, Peihao Huang, and Xin Wang
Author(s): Guo Xuan Chan, Peihao Huang, and Xin Wang

Superexchange is one of the vital resources to realize long-range interaction between distant spins for large-scale quantum computing. Recent experiments have demonstrated coherent oscillations between logical states defined by remote spins whose coupling is given by the superexchange interaction me…

[Phys. Rev. B 108, 035402] Published Wed Jul 05, 2023

Determination of the Zak phase of one-dimensional diffractive systems with inversion symmetry via radiation in Fourier space
C. Liu, H. R. Wang, and H. C. Ong
Author(s): C. Liu, H. R. Wang, and H. C. Ong

Bloch waves in one-dimensional periodic systems carry the Zak phase, which plays a key role in determining the band topology. In general, for a system that possesses inversion symmetry, the Zak phase of an isolated band is quantized as 0 or $π$ and is associated with the spatial-field symmetries of …

[Phys. Rev. B 108, 035403] Published Wed Jul 05, 2023

Thermal decomposition of the Kitaev material $α\text{−}{\mathrm{RuCl}}_{3}$ and its influence on low-temperature behavior
Franziska A. Breitner, Anton Jesche, Vladimir Tsurkan, and Philipp Gegenwart
Author(s): Franziska A. Breitner, Anton Jesche, Vladimir Tsurkan, and Philipp Gegenwart

We explore the effect of heat treatment in argon atmosphere under various temperatures up to $500{\phantom{\rule{0.16em}{0ex}}}^{∘}\mathrm{C}$ on single crystals of $α\text{−}{\mathrm{RuCl}}_{3}$ by the study of the mass loss, microprobe energy-dispersive x-ray spectroscopy, powder x-ray diffraction…

[Phys. Rev. B 108, 045103] Published Wed Jul 05, 2023

Entanglement in tripartitions of topological orders: A diagrammatic approach
Ramanjit Sohal and Shinsei Ryu
Author(s): Ramanjit Sohal and Shinsei Ryu

Recent studies have demonstrated that measures of tripartite entanglement can probe data characterizing topologically ordered phases to which bipartite entanglement is insensitive. Motivated by these observations, we compute the reflected entropy and logarithmic negativity, a mixed-state entanglemen…

[Phys. Rev. B 108, 045104] Published Wed Jul 05, 2023

Topological domain walls in graphene nanoribbons with carrier doping
Takuto Kawakami, Gen Tamaki, and Mikito Koshino
Author(s): Takuto Kawakami, Gen Tamaki, and Mikito Koshino

We theoretically study magnetic ground states of doped zigzag graphene nanoribbons and the emergence of topological domain walls. Using the Hartree-Fock mean-field approach and an effective continuum model, we demonstrated that the carrier doping stabilizes a magnetic structure with alternating anti…

[Phys. Rev. B 108, 045401] Published Wed Jul 05, 2023

Accurate force-field methodology capturing atomic reconstructions in transition metal dichalcogenide moiré system
Carl Emil Mørch Nielsen, Miguel da Cruz, Abderrezak Torche, and Gabriel Bester
Author(s): Carl Emil Mørch Nielsen, Miguel da Cruz, Abderrezak Torche, and Gabriel Bester

In this work, a generalized force-field methodology for the relaxation of large moiré heterostructures is proposed. The force-field parameters are optimized to accurately reproduce the structural degrees of freedom of some computationally manageable cells relaxed using density functional theory. The…

[Phys. Rev. B 108, 045402] Published Wed Jul 05, 2023

Chirality and correlations in the spontaneous spin-valley polarization of rhombohedral multilayer graphene
Yunsu Jang, Youngju Park, Jeil Jung, and Hongki Min
Author(s): Yunsu Jang, Youngju Park, Jeil Jung, and Hongki Min

We investigate the total energies of spontaneous spin-valley polarized states in bi-, tri-, and tetralayer rhombohedral graphene where the long-range Coulomb correlations are accounted for within the random phase approximation. Our analysis of the phase diagrams for varying carrier doping and perpen…

[Phys. Rev. B 108, L041101] Published Wed Jul 05, 2023

Found 1 papers in prl
Date of feed: Thu, 06 Jul 2023 03:17:06 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Tunable Interband Transitions in Twisted $h\text{−}\mathrm{BN}/\text{Graphene}$ Heterostructures
Bingyao Liu, Yu-Tian Zhang, Ruixi Qiao, Ruochen Shi, Yuehui Li, Quanlin Guo, Jiade Li, Xiaomei Li, Li Wang, Jiajie Qi, Shixuan Du, Xinguo Ren, Kaihui Liu, Peng Gao, and Yu-Yang Zhang
Author(s): Bingyao Liu, Yu-Tian Zhang, Ruixi Qiao, Ruochen Shi, Yuehui Li, Quanlin Guo, Jiade Li, Xiaomei Li, Li Wang, Jiajie Qi, Shixuan Du, Xinguo Ren, Kaihui Liu, Peng Gao, and Yu-Yang Zhang

In twisted $h\text{−}\mathrm{BN}/\text{graphene}$ heterostructures, the complex electronic properties of the fast-traveling electron gas in graphene are usually considered to be fully revealed. However, the randomly twisted heterostructures may also have unexpected transition behaviors, which may in…

[Phys. Rev. Lett. 131, 016201] Published Wed Jul 05, 2023

Found 1 papers in pr_res
Date of feed: Thu, 06 Jul 2023 03:17:07 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Berry curvature associated to Fermi arcs in continuum and lattice Weyl systems
Dennis Wawrzik and Jeroen van den Brink
Author(s): Dennis Wawrzik and Jeroen van den Brink

Recently it has been discovered that in Weyl semimetals the surface state Berry curvature can diverge in certain regions of momentum. This occurs in a continuum description of tilted Weyl cones, which for a slab geometry results in the Berry curvature dipole associated to the surface Fermi arcs grow…

[Phys. Rev. Research 5, 033007] Published Wed Jul 05, 2023