Found 50 papers in cond-mat
Date of feed: Mon, 27 Nov 2023 01:30:00 GMT

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Emergent chiral metal near a Kondo breakdown quantum phase transition. (arXiv:2311.13641v1 [cond-mat.str-el])
Tom Drechsler, Matthias Vojta

The destruction of the Kondo effect in a local-moment metal can lead to a topological non-Fermi-liquid phase, dubbed fractionalized Fermi liquid, with spinon-type excitations and an emergent gauge field. We demonstrate that, if the latter displays an internal $\pi$-flux structure, a chiral heavy-fermion metal naturally emerges near the Kondo-breakdown transition. Utilizing a parton mean-field theory describing the transition between a conventional heavy Fermi liquid and a U(1) fractionalized Fermi liquid, we find a novel intermediate phase near the transition whose emergent flux pattern spontaneously breaks both translation and time-reversal symmetries. This phase is an orbital antiferromagnet, and we discuss its relevance to pertinent experiments.


Qudit Stabilizer Codes, CFTs, and Topological Surfaces. (arXiv:2311.13680v1 [hep-th])
Matthew Buican, Rajath Radhakrishnan

We study general maps from the space of rational CFTs with a fixed chiral algebra and associated Chern-Simons (CS) theories to the space of qudit stabilizer codes with a fixed generalized Pauli group. We consider certain natural constraints on such a map and show that the map can be described as a graph homomorphism from an orbifold graph, which captures the orbifold structure of CFTs, to a code graph, which captures the structure of self-dual stabilizer codes. By studying explicit examples, we show that this graph homomorphism cannot always be a graph embedding. However, we construct a physically motivated map from universal orbifold subgraphs of CFTs to operators in a generalized Pauli group. We show that this map results in a self-dual stabilizer code if and only if the surface operators in the bulk CS theories corresponding to the CFTs in question are self-dual. For CFTs admitting a stabilizer code description, we show that the full abelianized generalized Pauli group can be obtained from twisted sectors of certain 0-form symmetries of the CFT. Finally, we connect our construction with SymTFTs, and we argue that many equivalences between codes that arise in our setup correspond to equivalence classes of bulk topological surfaces under fusion with invertible surfaces.


Fractional Quantum Hall State at Filling Factor $\nu=1/4$ in Ultra-High-Quality GaAs 2D Hole Systems. (arXiv:2311.13689v1 [cond-mat.mes-hall])
Chengyu Wang, A. Gupta, S. K. Singh, P. T. Madathil, Y. J. Chung, L. N. Pfeiffer, K. W. Baldwin, R. Winkler, M. Shayegan

Single-component fractional quantum Hall states (FQHSs) at even-denominator filling factors may host non-Abelian quasiparticles that are considered to be building blocks of topological quantum computers. Such states, however, are rarely observed in the lowest-energy Landau level, namely at filling factors $\nu<1$. Here we report evidence for an even-denominator FQHS at $\nu=1/4$ in ultra-high-quality two-dimensional hole systems confined to modulation-doped GaAs quantum wells. We observe a deep minimum in the longitudinal resistance at $\nu=1/4$, superimposed on a highly insulating background, suggesting a close competition between the $\nu=1/4$ FQHS and the magnetic-field-induced, pinned Wigner solid states. Our experimental observations are consistent with the very recent theoretical calculations which predict that substantial Landau level mixing, caused by the large hole effective mass, can induce composite fermion pairing and lead to a non-Abelian FQHS at $\nu=1/4$. Our results demonstrate that Landau level mixing can provide a very potent means for tuning the interaction between composite fermions and creating new non-Abelian FQHSs.


Nonrelaxational FMR peak broadening in spatially inhomogeneous films. (arXiv:2311.13733v1 [cond-mat.mes-hall])
Victor A. L'vov, Julia Kharlan, Vladimir O. Golub

The modification of magnetic properties in spatially inhomogeneous epitaxial films of magnetic shape memory alloys in martensitic state with the temperature variation has been studied. The proposed theoretical model is based on Landau theory of martensitic transformation and statistical model of martensitic state. It was shown that that spatial inhomogeneity of the material leads to the dispersion of local martensitic transformation temperatures resulting in the variation of local magnetic anisotropy values. This model allows describing the dramatic ferromagnetic resonance line broadening observed in the experiments in epitaxial films of magnetic shape memory alloys at low temperatures.


The valleytronic topological filters in silicene-like inner-edge systems. (arXiv:2311.13758v1 [cond-mat.mes-hall])
Hang Xie, Xiao-Long Lü, Jia-En Yang

Inner edge state with spin and valley degrees of freedom is a promising candidate to design a dissipationless device due to the topological protection. The central challenge for the application of inner edge state is to generate and modulate the polarized currents. In this work, we discover a new mechanism to generate fully valley- and spin-valley-polarized current caused by the Bloch wavevector mismatch (BWM). Based on this mechanism, we design some serial-typed inner-edge filters. With once of the BWM, the coincident states could be divided into transmitted and reflected modes, which can serve as a valley or spin-valley filter. In particular, while with twice of the BWM, the incident current is absolutely reflected to support an off state with a specified valley and spin, which is different from the gap effect. These findings give rise to a new platform for designing valleytronics and spin-valleytronics.


B63: the most stable bilayer structure with dual aromaticity. (arXiv:2311.13772v1 [cond-mat.mtrl-sci])
Jinhuang Chen, Rui Liao, Linwei Sai, Xue Wu, Jijun Zhao

The emergence of the first bilayer B48, which has been both theoretically predicted and experimentally observed, as well as the recent experimental synthesis of bilayer borophene on Ag and Cu, has generated tremendous curiosity in the bilayer structure of boron clusters. However, the connection between the bilayer cluster and the bilayer borophene remains unknown. By combining a genetic algorithm and density functional theory calculations, a global search for the low-energy structures of B63 clusters was conducted, revealing that the Cs bilayer structure with three interlayer B-B bonds was the most stable bilayer structure. This structure was further examined in terms of its structural stability, chemical bonding, and aromaticity. Interestingly, the interlayer bonds exhibited electronegativity and robust aromaticity. Furthermore, the double aromaticity stemmed from diatropic currents originating from virtual translational transitions at both the sigma and pi electrons. This new boron bilayer is anticipated to enrich the concept of double aromaticity and serve as a valuable precursor for bilayer borophene.


Quantum Hall and Light Responses in a 2D Topological Semimetal. (arXiv:2311.13922v1 [cond-mat.mes-hall])
Sariah Al Saati, Karyn Le Hur

We investigate the topological characteristics of a recently discovered class of semimetals in two dimensions on the honeycomb lattice. These semimetals reside at the transition between two distinct topological insulators, each existing in a nontrivial topological phase. As a result, these semimetals exhibit specific topological properties, including the presence of edge modes. In a preceding work, we demonstrated the topological robustness of this semimetal phase against disorder and interactions. In this work, we delve deeper into the semimetal's electronic properties, providing a precise calculation of its Hall conductivity and response to circularly polarized light, elaborating further on its bulk-edge correspondance leading to a half topological semimetal.


Semiclassical analysis of two-scale electronic Hamiltonians for twisted bilayer graphene. (arXiv:2311.14011v1 [math-ph])
Eric Cancès, Long Meng

This paper investigates the mathematical properties of independent-electron models for twisted bilayer graphene by examining the density-of-states of corresponding single-particle Hamiltonians using tools from semiclassical analysis. This study focuses on a specific atomic-scale Hamiltonian $H_{d,\theta}$ constructed from Density-Functional Theory, and a family of moir\'e-scale Hamiltonians $H_{d,K,\theta}^{\rm eff}$ containing the Bistritzer-MacDonald model. The parameter $d$ represents the interlayer distance, and $\theta$ the twist angle. It is shown that the density-of-states of $H_{d,\theta}$ and $H_{d,K,\theta}^{\rm eff}$ admit asymptotic expansions in the twist angle parameter $\epsilon:=\sin(\theta/2)$. The proof relies on a twisted version of the Weyl calculus and a trace formula for an exotic class of pseudodifferential operators suitable for the study of twisted 2D materials. We also show that the density-of-states of $H_{d,\theta}$ admits an asymptotic expansion in $\eta:=\tan(\theta/2)$ and comment on the differences between the expansions in $\epsilon$ and $\eta$.


Massive topological edge channels in three-dimensional topological materials induced by extreme surface anisotropy. (arXiv:2311.14069v1 [cond-mat.mes-hall])
Fengfeng Zhu, Chenqiang Hua, Xiao Wang, Lin Miao, Yixi Su, Makoto Hashimoto, Donghui Lu, Zhi-Xun Shen, Jin-Feng Jia, Yunhao Lu, Dandan Guan, Dong Qian

A two-dimensional quantum spin Hall insulator exhibits one-dimensional gapless spin-filtered edge channels allowing for dissipationless transport of charge and spin. However, the sophisticated fabrication requirement of two-dimensional materials and the low capacity of one-dimensional channels hinder the broadening applications. We introduce a method to manipulate a three-dimensional topological material to host a large number of one-dimensional topological edge channels utilizing surface anisotropy. Taking ZrTe5 as a model system, we realize a highly anisotropic surface due to the synergistic effect of the lattice geometry and Coulomb interaction, and achieve massive one-dimensional topological edge channels -- confirmed by electronic characterization using angle-resolved photoemission spectroscopy, in combination with first-principles calculations. Our work provides a new avenue to engineer the topological properties of three-dimensional materials through nanoscale tunning of surface morphology and opens up a promising prospect for the development of low-power-consumption electronic nano devices based on one-dimensional topological edge channels.


Two dimensional quantum lattice models via mode optimized hybrid CPU-GPU density matrix renormalization group method. (arXiv:2311.14106v1 [cond-mat.str-el])
Andor Menczer, Kornél Kapás, Miklós Antal Werner, Örs Legeza

We present a hybrid numerical approach to simulate quantum many body problems on two spatial dimensional quantum lattice models via the non-Abelian ab initio version of the density matrix renormalization group method on state-of-the-art high performance computing infrastructures. We demonstrate for the two dimensional spinless fermion model and for the Hubbard model on torus geometry that altogether several orders of magnitude in computational time can be saved by performing calculations on an optimized basis and by utilizing hybrid CPU-multiGPU parallelization. At least an order of magnitude reduction in computational complexity results from mode optimization, while a further order of reduction in wall time is achieved by massive parallelization. Our results are measured directly in FLOP and seconds. A detailed scaling analysis of the obtained performance as a function of matrix ranks and as a function of system size up to $12\times 12$ lattice topology is discussed.


Cosmic string influence on a 2D hydrogen atom and its relationship with the Rytova-Keldysh logarithmic approximation in semiconductors. (arXiv:2311.14144v1 [quant-ph])
Frankbelson dos S. Azevedo, Izael A. Lima, Gallileu Genesis, Rodolfo Casana, Edilberto O. Silva

A two-dimensional hydrogen atom offers a promising alternative for describing the quantum interaction between an electron and a proton in the presence of a straight cosmic string. Reducing the hydrogen atom to two dimensions enhances its suited to capture the cylindrical/conical symmetry associated with the cosmic string, providing a more appropriate description of the physical system. After solving Schr\"dinger's equation, we calculate the eigenenergies, probability distribution function, and expected values for the hydrogen atom with logarithmic potential under the influence of the topological defect. The calculations for the 2D hydrogen atom are performed for the first time using the Finite Difference Method. The results are presented through graphics, tables, and diagrams to elucidate the system's physical properties. We have verified that our calculations agree with a linear variational method result. Our model leads to an interesting analogy with excitons in a two-dimensional monolayer semiconductor located within a specific semiconductor region. To elucidate this analogy, we present and discuss some interaction potentials and their exciton eigenstates by comparing them with the results from the literature.


Bulk-edge correspondence for the nonlinear eigenvalues problem of the Haldane model. (arXiv:2311.14229v1 [cond-mat.dis-nn])
Shujie Cheng, Yonghua Jiang, Gao Xianlong

Recently, there is an interest in studying the bulk-edge correspondence for nonlinear eigenvalues problems in a two-dimensional topological system with spin-orbit coupling. By introducing auxiliary eigenvalues, the nonlinear bulk-edge correspondence was established. In this paper, taking the Haldane model as an example, we address that such a correspondence will appear in two dimensional topological system without spin-orbit coupling. The resulting edge states are characterized by the Chern number of the auxiliary energy band. A full phase diagram containing topological nontrivial phase, topological trivial phase, and metallic phase is obtained. Our work generalizes the study of the bulk-edge correspondence for nonlinear eigenvalue problems in two-dimensional system.


Identification of odd-frequency superconducting pairing in Josephson junctions. (arXiv:2311.14297v1 [cond-mat.mes-hall])
Subhajit Pal, Aabir Mukhopadhyay, Sourin Das

Choosing the right spin polarization of electron enables its local injection into the helical edge state with a well-defined momentum direction, despite the uncertainty principle, owing to spin-momentum locking. This fact facilitates a direct identification of odd-frequency pairing through parity measurement (under frequency reversal) of the anomalous Green's function in a setup comprising multi-terminal Josephson junction on the helical edge state of a 2D topological insulator.


Theory of fractional Chern insulator states in pentalayer graphene moir\'e superlattice. (arXiv:2311.14368v1 [cond-mat.str-el])
Zhongqing Guo, Xin Lu, Bo Xie, Jianpeng Liu

The experimental discoveries of fractional quantum anomalous Hall effects in both transition metal dichalcogenide and pentalayer graphene moir\'e superlattices have aroused significant research interest. In this work, we theoretically study the fractional quantum anomalous Hall states (also known as fractional Chern insulator states) in pentalayer graphene moir\'e superlattice. Starting from the highest energy scale ($\sim\!1\,$eV) of the continuum model, we first construct a renormalized low-energy model that applies to a lower cutoff $\sim\!0.15\,$eV using renormalization group approach. Then, we study the ground states of the renormalized low-energy model at filling 1 under Hartree-Fock approximation in the presence of tunable but self-consistently screend displacement field $D$ with several experimentally relevant background dielectric constant $\epsilon_r$. Two competing Hartree-Fock states are obtained at filling 1, which give rise to two types of topologically distrinct isolated flat bands with Chern number 1 and 0, respectively. We continue to explore the interacting ground states of the two types of isolated flat bands at hole dopings of 1/3, 2/5, 3/5, and 2/3 (corresponding electron fillings of 2/3, 3/5, 2/5, 1/3 with respect to charge neutrality). Our exact-diagonlization calculations suggest that the system stays in fractional Chern insulator (FCI) state at 2/3 electron filling when $0.9\,\textrm{V/nm}\leq\!D\!\leq 0.92\,\textrm{V/nm}$ and $5\lessapprox\epsilon_r\lessapprox 6$; while no robust FCI state is obtained at 1/3 electron filling in the experimentally relevant parameter regime. We have also obtained composite-fermion type FCI ground states at 3/5 electron filling within $0.9\,\textrm{V/nm}\leq\! D \!\leq\!0.96\,\textrm{V/nm}$ and $\epsilon_r\approx 5$. These numerical results are quantitatively consistent with experimental observations.


Electrically tunable correlated domain wall network in twisted bilayer graphene. (arXiv:2311.14384v1 [cond-mat.mes-hall])
Hao-Chien Wang, Chen-Hsuan Hsu

We investigate the domain wall network in twisted bilayer graphene (TBG) under the influence of interlayer bias and screening effect from the layered structure. Starting from the continuum model, we analyze the low-energy domain wall modes within the moir\'e bilayer structure and obtain an analytical form representing charge density distributions of the two-dimensional structure. With the efficient calculation of screened electron-electron interaction strengths both within and between the domain walls, we develop a bosonized model that describes the correlated domain wall network. We demonstrate that these interaction strengths can be modified through an applied interlayer bias, screening length and dielectric materials, and show how the model can be employed to investigate various properties of the domain wall network and its stability. This finding reveals the TBG network as a promising platform for the experimental manipulation of electron-electron interactions in low dimensions and the study of strongly correlated matter. We point out that the investigation not only enhances the understanding of domain wall modes in TBG but also has broader implications for the development of graphene-based devices.


Commensurate-incommensurate transition in frustrated Wigner crystals. (arXiv:2311.14396v1 [cond-mat.quant-gas])
Raphaël Menu, Jorge Yago Malo, Vladan Vuletić, Maria Luisa Chiofalo, Giovanna Morigi

Geometric frustration in systems with long-range interactions is a largely unexplored phenomenon. In this work we analyse the ground state emerging from the competition between a periodic potential and a Wigner crystal in one dimension, consisting of a selforganized chain of particles with the same charge. This system is a paradigmatic realization of the Frenkel-Kontorova model with Coulomb interactions. We derive the action of a Coulomb soliton in the continuum limit and demonstrate the mapping to a massive (1+1) Thirring model with long-range interactions. Here, the solitons are charged fermionic excitations over an effective Dirac sea. The mismatch between the periodicities of potential and chain, giving rise to frustration, is a chemical potential whose amplitude is majorly determined by the Coulomb self-energy. The mean-field limit is a long-range antiferromagnetic spin chain with uniform magnetic field and predicts that the commensurate, periodic structures form a complete devil's staircase as a function of the charge density. Each step of the staircase correspond to the interval of stability of a stable commensurate phase and scales with the number $N$ of charges as $1/\ln N$. This implies that there is no commensurate-incommensurate phase transition in the thermodynamic limit. For finite systems, however, the ground state has a fractal structure that could be measured in experiments with laser-cooled ions in traps.


Effect of the depolarizing field on the domain structure of an improper ferroelectric. (arXiv:2311.14429v1 [cond-mat.mtrl-sci])
Aaron Merlin Müller, Amadé Bortis, Manfred Fiebig, Thomas Lottermoser

We show that, contrary to common belief, the depolarizing electric field generated by bound charges at thin-film surfaces can have a substantial impact on the domain structure of an improper ferroelectric with topological defects. In hexagonal-manganite thin films, we observe in phase-field simulations that through the action of the depolarizing field, (i) the average magnitude of the polarization density decreases, (ii) the local magnitude of the polarization density decreases with increasing distance from the domain walls, and (iii) there is a significant alteration of the domain-size distribution, which is visualized with the pair-correlation function. We conclude that, in general, it is not appropriate to ignore the effects of the depolarizing field for thin film ferroelectrics.


Correlation between microstructural deformation mechanisms and acoustic parameters on a cold-rolled Cu30Zn brass. (arXiv:2311.14430v1 [cond-mat.mtrl-sci])
Maria Sosa, Linton Carvajal, Vicente Salinas, Fernando Lund, Claudio Aguilar, Felipe Castro

The relationship between acoustic parameters and the microstructure of a Cu30Zn brass plate subjected to plastic deformation was evaluated. The plate, previously annealed at 550 {\deg}C for 30 minutes, was cold rolled to reductions in the 10-70\% range. Using the pulse-echo method, linear ultrasonic measurements were performed on each of the nine specimens, corresponding to the nine different reductions, recording the wave times of flight of longitudinal wave along the thickness axis. Subsequently, acoustic measurements were performed to determine the nonlinear parameter ($\beta$) through the second harmonic generation. X-ray diffraction analysis revealed a steady increase and subsequent saturation of deformation twins at 40\% thickness reduction. At higher deformations, the microstructure revealed the generation and proliferation of shear bands, which coincided with a decrease in the twinning structure and an increase in dislocation density rate. Longitudinal wave velocity exhibited a 0.9\% decrease at 20\% deformation, followed by a continuous increase of 2\% beyond this point. These results can be rationalized as a competition between a proliferation of dislocations, which tends to decrease the linear sound velocity, and a decrease in average grain size, which tends to increase it. These variations are in agreement with the values obtained with XRD, Vickers hardness and metallography measurements. The nonlinear parameter $\beta$ shows a significant maximum, at the factor of 8 level, at 40\% deformation. This maximum correlates well with a similar maximum, at a factor of ten level and also at 40\% deformation, of the twinning fault probability.


Solid-that-flows picture of glass-forming liquids. (arXiv:2311.14460v1 [cond-mat.soft])
Jeppe C. Dyre

This article reviews arguments that glass-forming liquids are different from those of standard liquid-state theory. The latter typically have a viscosity in the mPa$\cdot$s range and relaxation times of order picoseconds, while these numbers grow dramatically and become $10^{12}-10^{15}$ times larger for liquids cooled toward the glass transition. This translates into a qualitative difference, and below the ``solidity length'' which is of order one micron at the glass transition, a glass-forming liquid behaves much like a solid. Recent numerical evidence for the solidity of ultraviscous liquids is reviewed, and experimental consequences are discussed in relation to dynamic heterogeneity, frequency-dependent linear-response functions, and the temperature dependence of the average relaxation time.


Multiple superconducting phases driven by pressure in the topological insulator GeSb4Te7. (arXiv:2311.14472v1 [cond-mat.supr-con])
W. Zhou, B. Li, Y. Shen, J. J. Feng, C. Q. Xu, H. T. Guo, Z. He, B. Qian, Ziming Zhu, Xiaofeng Xu

Tuning superconductivity in topological materials by means of chemical substitution, electrostatic gating, or pressure is thought to be an effective route towards realizing topological superconductivity with their inherent Majorana fermions, the manipulation of which may form the basis for future topological quantum computing. It has recently been established that the pseudo-binary chalcogenides (ACh)m(Pn2Ch3)n (A = Ge, Mn, Pb, etc.; Pn = Sb or Bi; Ch = Te, Se) may host novel topological quantum states such as the quantum anomalous Hall effect and topological axion states. Here we map out the phase diagram of one member in this series, the topological insulator candidate GeSb4Te7 up to pressures of ~35 GPa, through a combination of electrical resistance measurements, Raman spectroscopy, as well as first-principles calculations. Three distinct superconducting phases emerge under the pressure above ~11, ~17, and ~31 GPa, which are accompanied by concomitant structural transitions, evidenced from the changes in the Raman modes. The first-principles calculations validate the existence of a topological insulating state at ambient pressure and predict two possible structural transitions at 10 and 17 GPa, in agreement with the experimental observations. Overall, our results establish the GeSb4Te7 family of materials as a fertile arena for further exploring various topological phenomena, including topological phase transitions and putative topological superconductivity.


Back-action supercurrent diodes. (arXiv:2311.14503v1 [cond-mat.mes-hall])
Daniel Margineda, Alessandro Crippa, Elia Strambini, Yuri Fukaya, Maria Teresa Mercaldo, Carmine Ortix, Mario Cuoco, Francesco Giazotto

Back-action refers to a response that retro-acts on a system to tailor its properties with respect to an external stimulus. This self-induced effect generally belongs to both the natural and technological realm, ranging from neural networks to optics and electronic circuitry. In electronics, back-action mechanisms are at the heart of many classes of devices such as amplifiers, oscillators, and sensors. Here, we demonstrate that back-action can be successfully exploited to achieve $\textit{non-reciprocal}$ transport in superconducting circuits. Our device realizes a supercurrent diode, since the dissipationless current flows in one direction whereas dissipative transport occurs in the opposite direction. Supercurrent diodes presented so far rely on magnetic elements or vortices to mediate charge transport or external magnetic fields to break time-reversal symmetry. In our implementation, back-action solely turns a conventional reciprocal superconducting weak link with no asymmetry between the current bias directions into a diode, where the critical current amplitude depends on the bias sign. The self-interaction of the supercurrent with the device stems from the gate tunability of the critical current, which uniquely promotes up to $\sim$88% of magnetic field-free signal rectification and diode functionality with selectable polarity. The concept we introduce is very general and can be applied directly to a large variety of devices, thereby opening novel functionalities in superconducting electronics.


Topological quantum thermometry. (arXiv:2311.14524v1 [quant-ph])
Anubhav Kumar Srivastava, Utso Bhattacharya, Maciej Lewenstein, Marcin Płodzień

An optimal local quantum thermometer is a quantum many-body system that saturates the fundamental lower bound for the thermal state temperature estimation accuracy [L. Correa, et. al., Phys. Rev. Lett. 114, 220405 (2015)]. Such a thermometer has a particular energy level structure with a single ground state and highly degenerated excited states manifold, with an energy gap proportional to the estimated temperature. In this work, we show that the optimal local quantum thermometer can be realized in an experimentally feasible system of spinless fermions confined in a one-dimensional optical lattice described by the Rice-Mele model. We characterize the system's sensitivity to temperature changes in terms of quantum Fisher information and the classical Fisher information obtained from experimentally available site occupation measurements.


Ground states of one-dimensional dipolar lattice bosons at unit filling. (arXiv:2311.14606v1 [cond-mat.quant-gas])
Mateusz Łącki, Henning Korbmacher, G. A. Domínguez-Castro, Jakub Zakrzewski, Luis Santos

Recent experiments on ultracold dipoles in optical lattices open exciting possibilities for the quantum simulation of extended Hubbard models. When considered in one dimension, these models present at unit filling a particularly interesting ground-state physics, including a symmetry-protected topological phase known as Haldane insulator. We show that the tail of the dipolar interaction beyond nearest-neighbors, which may be tailored by means of the transversal confinement, does not only modify quantitatively the Haldane insulator regime and lead to density waves of larger periods, but results as well in unexpected insulating phases. These insulating phases may be topological or topologically trivial, and are characterized by peculiar correlations of the site occupations. These phases may be realized and observed in state-of-the-art experiments.


Emergent Topology in Many-Body Dissipative Quantum Chaos. (arXiv:2311.14640v1 [cond-mat.str-el])
Antonio M. García-García, Lucas Sá, Jacobus J. M. Verbaarschot, Can Yin

The identification, description, and classification of topological features is an engine of discovery and innovation in several fields of physics. This research encompasses a broad variety of systems, from the integer and fractional Chern insulators in condensed matter, to protected states in complex photonic lattices in optics, and the structure of the QCD vacuum. Here, we introduce another playground for topology: the dissipative dynamics of the Sachdev-Ye-Kitaev (SYK) model, $N$ fermions in zero dimensions with strong $q$-body interactions coupled to a Markovian bath. For $q = 4, 8, \ldots$ and certain choices of $N$ and bath details, involving pseudo-Hermiticity, we find a rectangular block representation of the vectorized Liouvillian that is directly related to the existence of an anomalous trace of the unitary operator implementing fermionic exchange. As a consequence of this rectangularization, the Liouvillian has purely real modes for any coupling to the bath. Some of them are demonstrated to be topological by an explicit calculation of the spectral flow, leading to a symmetry-dependent topological index $\nu$. Topological properties have universal features: they are robust to changes in the Liouvillian provided that the symmetries are respected and they are also observed if the SYK model is replaced by a quantum chaotic dephasing spin chain in the same symmetry class. Moreover, the topological symmetry class can be robustly characterized by the level statistics of the corresponding random matrix ensemble. In the limit of weak coupling to the bath, topological modes govern the approach to equilibrium, which may enable a direct path for experimental confirmation of topology in dissipative many-body quantum chaotic systems.


Relativistic Tight-Binding Model for Hexagonal Lattice: Application to Graphene. (arXiv:2204.06836v3 [cond-mat.mtrl-sci] UPDATED)
Rohin Sharma, Amit Shrestha, Masahiko Higuchi, Katsuhiko Higuchi, Dipendra B. Hamal

A non-perturbative relativistic tight-binding (TB) approximation method applicable to crystalline material immersed in a magnetic field was developed in 2015. To apply this method to any material in the magnetic field, the electronic structure of the material in absence of a magnetic field must be calculated. In this study, we present the relativistic TB approximation method for graphene in a zero magnetic field. The Hamiltonian and overlap matrix is constructed considering the nearest neighbouring atomic interactions between the $s$ and $p$ valence orbitals, where the relativistic hopping and overlap integrals are calculated using the relativistic version of the Slater-Koster table. The method of constructing the Hamiltonian and overlap matrix and the resulting energy-band structure of graphene in the first Brillouin zone is presented in this paper. It is found that there is an appearance of a small band-gap at the $\textbf{K}$ points (also known as the spin-orbit gap) due to the relativistic effect, whose magnitude is $25$ $\mu$eV.


A symmetry principle for gauge theories with fractons. (arXiv:2207.00854v3 [cond-mat.str-el] UPDATED)
Yuji Hirono, Minyoung You, Stephen Angus, Gil Young Cho

Fractonic phases are new phases of matter that host excitations with restricted mobility. We show that a certain class of gapless fractonic phases are realized as a result of spontaneous breaking of continuous higher-form symmetries whose conserved charges do not commute with spatial translations. We refer to such symmetries as nonuniform higher-form symmetries. These symmetries fall within the standard definition of higher-form symmetries in quantum field theory, and the corresponding symmetry generators are topological. Worldlines of particles are regarded as the charged objects of 1-form symmetries, and mobility restrictions can be implemented by introducing additional 1-form symmetries whose generators do not commute with spatial translations. These features are realized by effective field theories associated with spontaneously broken nonuniform 1-form symmetries. At low energies, the theories reduce to known higher-rank gauge theories such as scalar/vector charge gauge theories, and the gapless excitations in these theories are interpreted as Nambu--Goldstone modes for higher-form symmetries. Due to the nonuniformity of the symmetry, some of the modes acquire a gap, which is the higher-form analogue of the inverse Higgs mechanism of spacetime symmetries. The gauge theories have emergent nonuniform magnetic symmetries, and some of the magnetic monopoles become fractonic. We identify the 't~Hooft anomalies of the nonuniform higher-form symmetries and the corresponding bulk symmetry-protected topological phases. By this method, the mobility restrictions are fully determined by the choice of the commutation relations of charges with translations. This approach allows us to view existing (gapless) fracton models such as the scalar/vector charge gauge theories and their variants from a unified perspective and enables us to engineer theories with desired mobility restrictions.


Effects of spatial dimensionality and band tilting on the longitudinal optical conductivities in Dirac bands. (arXiv:2210.10410v2 [cond-mat.mes-hall] UPDATED)
Jian-Tong Hou, Chang-Xu Yan, Chao-Yang Tan, Zhi-Qiang Li, Peng Wang, Hong Guo, Hao-Ran Chang

We report a unified theory based on linear response, for analyzing the longitudinal optical conductivity (LOC) of materials with tilted Dirac cones. Depending on the tilt parameter $t$, the Dirac electrons have four phases: untilted, type-I, type-II, and type-III; the Dirac dispersion can be isotropic or anisotropic; the spatial dimension of the material can be one-, two-, or three-dimensions (1D, 2D and 3D). The interband LOCs and intraband LOCs in $d$ dimension (with $d\ge2$) are found to scale as $\sigma_{0}\omega^{d-2}$ and $\sigma_{0}\mu^{d-1}\delta(\omega)$, respectively, where $\omega$ is the frequency and $\mu$ the chemical potential. The interband LOC vanishes in 1D due to lack of extra spatial dimension. In contrast, the interband LOCs in 2D and 3D are nonvanishing and share many similar properties. A universal and robust fixed point of interband LOCs appears at $\omega=2\mu$ no matter $d=2$ or $d=3$, which can be intuitively understood by the geometric structures of Fermi surface and energy resonance contour. The intraband LOCs and the carrier density for 2D and 3D tilted Dirac bands are both closely related to the geometric structure of Fermi surface and the cutoff of integration. The angular dependence of LOCs is found to characterize both spatial dimensionality and band tilting and the constant asymptotic background values of LOC reflect features of Dirac bands. The LOCs in the anisotropic tilted Dirac cone can be connected to its isotropic counterpart by a ratio that consists of Fermi velocities for both 2D and 3D. Most of the findings are universal for tilted Dirac materials and hence valid for a great many Dirac materials in the spatial dimensions of physical interest.


Mott insulators with boundary zeros. (arXiv:2301.05588v2 [cond-mat.str-el] UPDATED)
Niklas Wagner, Lorenzo Crippa, Adriano Amaricci, Philipp Hansmann, Marcel Klett, Elio König, Thomas Schäfer, Domenico Di Sante, Jennifer Cano, Andrew Millis, Antoine Georges, Giorgio Sangiovanni

The topological classification of electronic band structures is based on symmetry properties of Bloch eigenstates of single-particle Hamiltonians. In parallel, topological field theory has opened the doors to the formulation and characterization of non-trivial phases of matter driven by strong electron-electron interaction. Even though important examples of topological Mott insulators have been constructed, the relevance of the underlying non-interacting band topology to the physics of the Mott phase has remained unexplored. Here, we show that the momentum structure of the Green's function zeros defining the ``Luttinger surface" provides a topological characterization of the Mott phase related, in the simplest description, to the one of the single-particle electronic dispersion. Considerations on the zeros lead to the prediction of new phenomena: a topological Mott insulator with an inverted gap for the bulk zeros must possess gapless zeros at the boundary, which behave as a form of ``topological antimatter'' annihilating conventional edge states. Placing band and Mott topological insulators in contact produces distinctive observable signatures at the interface, revealing the otherwise spectroscopically elusive Green's function zeros.


Dirac equation in curved spacetime: the role of local Fermi velocity. (arXiv:2301.12952v3 [cond-mat.mes-hall] UPDATED)
B. Bagchi, A. Gallerati, R. Ghosh

We study the motion of charge carriers in curved Dirac materials, in the presence of a local Fermi velocity. An explicit parameterization of the latter emerging quantity for a nanoscroll cylindrical geometry is also provided, together with a discussion of related physical effects and observable properties.


Light-matter correlations in Quantum Floquet engineering. (arXiv:2302.12290v2 [cond-mat.mes-hall] UPDATED)
Beatriz Pérez-González, Gloria Platero, Álvaro Gómez-León

Quantum Floquet engineering seeks to externally control systems by means of quantum fields. However, to faithfully capture the physics at arbitrary coupling, a gauge-invariant description of light-matter interaction is required, which makes the Hamiltonian highly nonlinear in the photonic operators. Here we provide a non-perturbative truncation scheme, which is valid for arbitrary coupling strength. With this framework, we investigate the role of light-matter correlations, which are absent in systems described by semiclassical Floquet engineering. We find that even in the high-frequency regime, their importance can be crucial, in particular for the topological properties of the system. As an example we show that in an SSH chain coupled to a cavity, light-matter correlations break chiral symmetry, strongly affecting the robustness of its edge states. In addition, we show how light-matter correlations are imprinted in the photonic spectral function, and discuss their relation with the topology of the photonic bands.


Experimental investigation of the effect of topological insulator on the magnetization dynamics of ferromagnetic metal: $BiSbTe_{1.5}Se_{1.5}$ and $Ni_{80}Fe_{20}$ heterostructure. (arXiv:2303.07025v2 [cond-mat.mes-hall] UPDATED)
Sayani Pal, Soumik Aon, Subhadip Manna, Sambhu G Nath, Kanav Sharma, Chiranjib Mitra

We have studied ferromagnetic metal/topological insulator bilayer system to understand magnetization dynamics of ferromagnetic metal (FM) in contact with a topological insulator (TI). At magnetic resonance condition, the precessing magnetization in the metallic ferromagnet ($Ni_{80}Fe_{20}$) injects spin current into the topological insulator ($BiSbTe_{1.5}Se_{1.5}$), a phenomenon known as spin-pumping. Due to the spin pumping effect, fast relaxation in the ferromagnet results in the broadening of ferromagnetic resonance linewidth ($\Delta H$). We evaluated the parameters like effective Gilbert damping coefficient ($\alpha_{eff}$), spin-mixing conductance ($g_{eff}^{\uparrow \downarrow}$) and spin current density ($j_S^0$) to confirm a successful spin injection due to spin-pumping into the $BiSbTe_{1.5}Se_{1.5}$ layer. TIs embody a spin-momentum locked surface state that span the bulk band-gap. It can act differently to the FM magnetization than the other normal metals. To probe the effect of topological surface state, a systematic low temperature study is crucial as surface state of TI dominates at lower temperatures. The exponential growth of $\Delta H$ for all different thickness combination of FM/TI bilayers and effective Gilbert damping coefficient ($\alpha_{eff}$) with lowering temperature confirms the prediction that spin chemical bias generated from spin-pumping induces surface current in TI due to spin-momentum locking. The hump-like feature of magnetic anisotropy field ($H_K$)of the bilayer around 60K suggests that the decrease of interfacial in-plane magnetic anisotropy can result from exchange coupling between the TI surface state and the local moments of FM layer.


Coherent Charge Oscillations in a Bilayer Graphene Double Quantum Dot. (arXiv:2303.10119v4 [cond-mat.mes-hall] UPDATED)
Katrin Hecker, Luca Banszerus, Aaron Schäpers, Samuel Möller, Anton Peters, Eike Icking, Kenji Watanabe, Takashi Taniguchi, Christian Volk, Christoph Stampfer

The coherent dynamics of a quantum mechanical two-level system passing through an anti-crossing of two energy levels can give rise to Landau-Zener-St\"uckelberg-Majorana (LZSM) interference. LZSM interference spectroscopy has proven to be a fruitful tool to investigate charge noise and charge decoherence in semiconductor quantum dots (QDs). Recently, bilayer graphene has developed as a promising platform to host highly tunable QDs potentially useful for hosting spin and valley qubits. So far, in this system no coherent oscillations have been observed and little is known about charge noise in this material. Here, we report coherent charge oscillations and $T_2^*$ charge decoherence times in a bilayer graphene double QD. The charge decoherence times are measured independently using LZSM interference and photon assisted tunneling. Both techniques yield $T_2^*$ average values in the range of 400 to 500 ps. The observation of charge coherence allows to study the origin and spectral distribution of charge noise in future experiments.


Designing nontrivial one-dimensional Floquet topological phases using a spin-1/2 double-kicked rotor. (arXiv:2303.13982v2 [cond-mat.quant-gas] UPDATED)
Yusuke Koyama, Kazuya Fujimoto, Shuta Nakajima, Yuki Kawaguchi

A quantum kicked rotor model is one of the promising systems to realize various Floquet topological phases. We consider a double-kicked rotor model for a one-dimensional quasi-spin-1/2 Bose-Einstein condensate with spin-dependent and spin-independent kicks which are implementable for cold atomic experiments. We theoretically show that the model can realize all the Altland-Zirnbauer classes with nontrivial topology in one dimension. In the case of class CII, we show that a pair of winding numbers $(w_0,w_\pi)\in 2\mathbb{Z}\times 2\mathbb{Z}$ featuring the edge states at zero and $\pi$ quasienergy, respectively, takes various values depending on the strengths of the kicks. We also find that the winding numbers change to $\mathbb{Z}$ when we break the time-reversal and particle-hole symmetries by changing the phase of a kicking lattice. We numerically confirm that the winding numbers can be obtained by measuring the mean chiral displacement in the long-time limit in the present case with four internal degrees of freedom. We further propose two feasible methods to experimentally realize the spin-dependent and spin-independent kicks required for various topological phases.


Highly anisotropic optical conductivities in two-dimensional tilted semi-Dirac bands. (arXiv:2303.18155v2 [cond-mat.mes-hall] UPDATED)
Chang-Xu Yan, Chao-Yang Tan, Hong Guo, Hao-Ran Chang

Within linear response theory, the absorptive part of highly anisotropic optical conductivities are analytically calculated for distinct tilts in two-dimensional (2D) tilted semi-Dirac bands (SDBs). The transverse optical conductivities always vanish. The interband longitudinal optical conductivities (LOCs) in 2D tilted SDBs differ qualitatively in the power-law scaling of $\omega$ as $\mathrm{Re}\sigma_{\perp}^{\mathrm{IB}}(\omega)\propto\sigma_0\sqrt{\omega}$ and $\mathrm{Re}\sigma_{\parallel}^{\mathrm{IB}}(\omega)\propto\sigma_0/\sqrt{\omega}$. By contrast, the intraband LOCs in 2D tilted SDBs depend on $\mu$ in the power-law scaling as $\mathrm{Re}\sigma_{\perp}^{\mathrm{D}}(\omega)\propto\sigma_0\mu \sqrt{\mu}$ and $\mathrm{Re}\sigma_{\parallel}^{\mathrm{D}}(\omega)\propto\sigma_0\mu/\sqrt{\mu}$. The tilt-dependent behaviors of LOCs could qualitatively characterize distinct impact of band tilting in 2D tilted SDBs. In particular, for arbitrary tilt $t$ satisfying $0<t\le 2$, the interband LOCs always possess a robust fixed point at $\omega=2\mu$. The power-law scalings and tilt-dependent behaviors further dictate significant differences in the asymptotic background values and angular dependence of LOCs. Our theoretical predictions should be valid for a broad class of 2D tilted SDB materials, and can also be used to fingerprint 2D tilted SDB from 2D untilted SDB as well as tilted Dirac bands.


Magnon-magnon interaction in monolayer MnBi$_2$Te$_4$. (arXiv:2304.09637v3 [cond-mat.str-el] UPDATED)
Yiqun Liu, Liangjun Zhai, Songsong Yan, Di Wang, Xiangang Wan

MnBi$_2$Te$_4$, the first confirmed intrinsic antiferromagnetic topological insulator, has garnered increasing attention in recent years. Here we investigate the energy correction and lifetime of magnons in MnBi$_2$Te$_4$ caused by magnon-magnon interaction. First, a calculation based on the density functional theory was performed to get the parameters of the magnetic Hamiltonian of MnBi$_2$Te$_4$. Subsequently, the perturbation method of many-body Green's function was employed and the first-order self-energy [$\Sigma^{(1)}(\bm k)$] and second-order self-energy [$\Sigma^{(2)}(\bm k,\varepsilon_{\bm k})$] of magnon were obtained. Numerical computations reveal that the corrections from both $\Sigma^{(1)}(\bm k)$ and $\Sigma^{(2)}(\bm k,\varepsilon_{\bm k})$ strongly rely on momentum and temperature, with the energy renormalization near the Brillouin zone (BZ) boundary being significantly more pronounced than that near the BZ center. Furthermore, our findings indicate the occurrence of dip structures in the renormalized magnon spectrum near the $\rm K$ and $\rm M$ points. These dip structures are determined to be attributed to the influence of $\Sigma^{(2)}(\bm k,\varepsilon_{\bm k})$.


From Ergodicity to Many-Body Localization in a One-Dimensional Interacting Non-Hermitian Stark System. (arXiv:2305.13636v3 [cond-mat.dis-nn] UPDATED)
Jinghu Liu, Zhihao Xu

Recent studies on disorder-induced many-body localization (MBL) in non-Hermitian quantum systems have attracted great interest. However, the non-Hermitian disorder-free MBL still needs to be clarified. We consider a one-dimensional interacting Stark model with nonreciprocal hoppings having time-reversal symmetry, the properties of which are boundary dependent. Under periodic boundary conditions (PBCs), such a model exhibits three types of phase transitions: the real-complex transition of eigenenergies, the topological phase transition, and the non-Hermitian Stark MBL transition. The real-complex and topological phase transitions occur at the same point in the thermodynamic limit but do not coincide with the non-Hermitian Stark MBL transition, which is quite different from the non-Hermitian disordered cases. By the level statistics, the system transitions from the Ginibre ensemble (GE) to the Gaussian orthogonal ensemble (GOE) to the Possion ensemble with the increase of the linear tilt potential's strength. The real-complex transition of the eigenvalues is accompanied by the GE-to-GOE transition in the ergodic regime. Moreover, the second transition of the level statistics corresponds to the occurrence of non-Hermitian Stark MBL. We demonstrate that the non-Hermitian Stark MBL is robust and shares many similarities with disorder-induced MBL, which several existing characteristic quantities of the spectral statistics and eigenstate properties can confirm. The dynamical evolutions of the entanglement entropy and the density imbalance can distinguish the real-complex and Stark MBL transitions. Finally, we find that our system under open boundary conditions lacks a real-complex transition, and the transition of non-Hermitian Stark MBL is the same as that under PBCs.


Shift photoconductivity in the Haldane model. (arXiv:2305.17035v2 [cond-mat.mes-hall] UPDATED)
Javier Sivianes (1), Julen Ibañez-Azpiroz (1 and 2) ((1) Centro de Física de Materiales (CSIC-UPV/EHU), Donostia-San Sebastián, Spain, (2) Ikerbasque Foundation, Bilbao, Spain)

The shift current is part of the second-order optical response of materials with a close connection to topology. Here we report a sign inversion in the band-edge shift photoconductivity of the Haldane model when the system undergoes a topological phase transition. This result is obtained following two complementary schemes. On one hand, we derive an analytical expression for the band-edge shift current in a two-band tight-binding model showing that the sign reversal is driven by the mass term. On the other hand, we perform a numerical evaluation on a continuum version of the Haldane model. This approach allows us to include off-diagonal matrix elements of the position operator, which are discarded in tight-binding models but can contribute significantly to the shift current. Explicit evaluation of the shift current shows that while the model predictions remain accurate in the deep tight-binding regime, significant deviations arise for shallow potential landscapes. Notably, the sign reversal across the topological phase transition is observed in all regimes, implying it is a robust effect that could be observable in a wide range of topological insulators.


Universal defect density scaling in an oscillating dynamic phase transition. (arXiv:2306.03803v4 [cond-mat.stat-mech] UPDATED)
Wei-can Yang, Makoto Tsubota, Adolfo del Campo, Hua-Bi Zeng

Universal scaling laws govern the density of topological defects generated while crossing an equilibrium continuous phase transition. The Kibble-Zurek mechanism (KZM) predicts the dependence on the quench time for slow quenches. By contrast, for fast quenches, the defect density scales universally with the amplitude of the quench. We show that universal scaling laws apply to dynamic phase transitions driven by an oscillating external field. The difference in the energy response of the system to a periodic potential field leads to energy absorption, spontaneous breaking of symmetry, and its restoration. We verify the associated universal scaling laws, providing evidence that the critical behavior of non-equilibrium phase transitions can be described by time-average critical exponents combined with the KZM. Our results demonstrate that the universality of critical dynamics extends beyond equilibrium criticality, facilitating the understanding of complex non-equilibrium systems.


Piercing the Dirac spin liquid: From a single monopole to chiral states. (arXiv:2307.01149v2 [cond-mat.str-el] UPDATED)
Sasank Budaraju, Yasir Iqbal, Federico Becca, Didier Poilblanc

The parton approach for quantum spin liquids gives a transparent description of low-energy elementary excitations, e.g., spinons and emergent gauge-field fluctuations. The latter ones are directly coupled to the hopping/pairing of spinons. By using the fermionic representation of the $U(1)$ Dirac state on the kagome lattice and variational Monte Carlo techniques to include the Gutzwiller projection, we analyse the effect of modifying the gauge fields in the spinon kinematics. In particular, we construct low-energy monopole excitations, which are shown to be gapless in the thermodynamic limit. States with a finite number of monopoles or with a finite density of them are also considered, with different patterns of the gauge fluxes. We show that these chiral states are not stabilized in the Heisenberg model with nearest-neighbor super-exchange couplings, and the Dirac state corresponds to the lowest-energy Ansatz within this family of variational wave functions. Our results support the idea that spinons with a gapless conical spectrum coexist with gapless monopole excitations, even for the spin-1/2 case.


The topological Kondo model out of equilibrium. (arXiv:2307.03773v2 [cond-mat.str-el] UPDATED)
Matteo M. Wauters, Chia-Min Chung, Lorenzo Maffi, Michele Burrello

The topological Kondo effect is a genuine manifestation of the nonlocality of Majorana modes. We investigate its out-of-equilibrium signatures in a model with a Cooper-pair box hosting four of these topological modes, each connected to a metallic lead. Through an advanced matrix-product-state approach tailored to study the dynamics of superconductors, we simulate the relaxation of the Majorana magnetization, which allows us to determine the related Kondo temperature, and we analyze the onset of electric transport after a quantum quench of a lead voltage. Our results apply to Majorana Cooper-pair boxes fabricated in double nanowire devices and provide nonperturbative evidence of the crossover from weak-coupling states to the strongly correlated topological Kondo regime. The latter dominates at the superconductor charge degeneracy points and displays the expected universal fractional zero-bias conductance.


Emerging topological bound states in Haldane model zigzag nanoribbons. (arXiv:2307.14771v2 [cond-mat.mes-hall] UPDATED)
Simone Traverso, Maura Sassetti, Niccolò Traverso Ziani

Zigzag nanoribbons hosting the Haldane Chern insulator model are considered. In this context, an unreported reentrant topological phase, characterized by the emergence of quasi zero dimensional in-gap states, is discussed. The bound states, which reside in the gap opened by the hybridization of the counter-propagating edge modes of the Haldane phase, are localized at the ends of the strip and are found to be robust against on-site disorder. These findings are supported by the behavior of the Zak phase over the parameter space, which exhibits jumps of $\pi$ in correspondence to the phase transitions between the trivial and the non-trivial phases. The effective mass inversion leading to the jumps in the Zak phase is interpreted in a low energy framework. Setups with non-uniform parameters also show topological bound states via the Jackiw-Rebbi mechanism. All the properties reported are shown to be extremely sensitive to the strip width.


Selective Manipulation and Tunneling Spectroscopy of Broken-Symmetry Quantum Hall States in a Hybrid-edge Quantum Point Contact. (arXiv:2307.15728v3 [cond-mat.mes-hall] UPDATED)
Wei Ren, Xi Zhang, Jaden Ma, Xihe Han, Kenji Watanabe, Takashi Taniguchi, Ke Wang

We present a device architecture of hybrid-edge and dual-gated quantum point contact. We demonstrate improved electrostatic control over the separation, position, and coupling of each broken-symmetry compressible strip in graphene. Via low-temperature magneto-transport measurement, we demonstrate selective manipulation over the evolution, hybridization, and transmission of arbitrarily chosen quantum Hall states in the channel. With gate-tunable tunneling spectroscopy, we characterize the energy gap of each symmetry-broken quantum Hall state with high resolution on the order of ~0.1 meV.


The 1/4 occupied O atoms induced ultraflat band and the one dimensional channels in the Pb$_{10-x}$Cu$_{x}$(PO$_4$)$_{6}$O$_{4}$ (x=0,0.5) crystal. (arXiv:2308.03218v4 [cond-mat.supr-con] UPDATED)
Kun Tao, Rongrong Chen, Lei Yang, Jin Gao, Desheng Xue, Chenglong Jia

The search for room-temperature superconductors has been a long-standing goal in condensed matter physics. In this study, we investigate the electronic and geometric properties of lead apatite with and without Cu doped within the frame work of the density functional theory. Based on our calculations, we found that without the Cu doped the lead apatite shows an insulator character with flat bands straddle the Fermi level. Once we introduce the O1 vacancies, the flat bands disappear. Furthermore, we analyze the effects of Cu doping on the crystal structure and electronic band structure of the material. Our calculations reveal the presence of one-dimensional channels induced by fully occupied O1 atoms, that are only 1/4 occupied in the literature, which may play a crucial role in the realization of room-temperature superconductivity. Based on our findings, we propose a possible solution to improve the quality of superconductivity by annealing the material in an oxygen atmosphere. These results contribute to a better understanding of the unusual properties of Cu-doped lead apatite and will pave the way for further exploration of its potential as a room-temperature superconductor.


Biorthogonal Majorana zero modes, extended waves in continuum of bound states and non-Hermitian Toda soliton-fermion duality. (arXiv:2310.03215v2 [hep-th] UPDATED)
Harold Blas

We study the non-Hermitian (NH) Toda model coupled to fermions through soliton theory techniques and the realizations of the pseudo-chiral and pseudo-Hermitian symmetries. The interplay of non-Hermiticity, integrability, nonlinearity, and topology significantly influence the formation and behavior of a continuum of bound state modes (CBM) and extended waves in the localized continuum (ELC). The non-Hermitian soliton-fermion duality, the complex scalar field topological charges and winding numbers in the spectral topology are uncovered. The Hermitian bound states/solitons lie on the unit circle $|z|=1$ defined by the uniformization parameter $z \in \IC \backslash \{0\}$ related to the complex energy eigenvalue, whereas the non-Hermitian bound states/solitons lie on the complex plane such that $|z| \neq 1$. The biorthogonal Majorana zero modes, dual to the NH Toda solitons with topological charges $\pm 1$, appear at the complex-energy point gap and are pinned at zero energy. The regions of $\IC\backslash \{0\}$ with real eigenvalues are uncovered, and these come in real pairs $\pm \l_1\, (\l_1 \in \IR)$ preserving the pseudo-chiral symmetry. Our findings improve the understanding of exotic quantum states, but also paves the way for future research in harnessing non-Hermitian phenomena for topological quantum computation, as well as the exploration of integrability and NH solitons in the theory of topological phases of matter.the theory of topological phases of matter.


Designing Moir\'e Patterns by Bending. (arXiv:2310.13743v2 [cond-mat.mes-hall] UPDATED)
Pierre A. Pantaleón, Héctor Sainz-Cruz, Francisco Guinea

Motivated by a recent experiment [Kapfer et. al., Science {\bf 381}, 677 (2023)], we analyze the structural effects and low-energy physics of a bent nanoribbon placed on top of graphene, which creates a gradually changing moir\'e pattern. By means of a classical elastic model we derive the strains in the ribbon and we obtain its spectrum with a scaled tight-binding model. The size of the bent region is determined by the balance between elastic and van der Waals energy, and different regimes are identified. Near the clamped edge, strong strains and small angles leads to one-dimensional channels. Near the bent edge, a long region behaves like magic angle twisted bilayer graphene (TBG), showing a sharp peak in the density of states, mostly isolated from the rest of the spectrum. We also calculate the band topology along the ribbon and we find that it is stable for large intervals of strains an twist angles. Together with the experimental observations, these results show that the bent nanoribbon geometry is ideal for exploring superconductivity and correlated phases in TBG in the very sought-after regime of ultra-low twist angle disorder.


Theory of fractional quantum anomalous Hall phases in pentalayer rhombohedral graphene moir\'e structures. (arXiv:2311.03445v2 [cond-mat.str-el] UPDATED)
Zhihuan Dong, Adarsh S. Patri, T. Senthil

Remarkable recent experiments on the moir\'e structure formed by pentalayer rhombohedral graphene aligned with a hexagonal Boron-Nitride substrate report the discovery of a zero field fractional quantum hall effect. These ``(Fractional) Quantum Anomalous Hall" ((F)QAH) phases occur for one sign of a perpendicular displacement field, and correspond, experimentally, to full or partial filling of a valley polarized Chern-$1$ band. Such a band is absent in the non-interacting band structure. Here we show that electron-electron interactions play a crucial role, and present microscopic theoretical calculations demonstrating the emergence of a nearly flat, isolated, Chern-$1$ band and FQAH phases in this system. We also study the four and six-layer analogs and identify parameters where a nearly flat isolated Chern-$1$ band emerges which may be suitable to host FQAH physics.


Fractional quantum anomalous Hall effects in rhombohedral multilayer graphene in the moir\'eless limit and in Coulomb imprinted superlattice. (arXiv:2311.04217v2 [cond-mat.str-el] UPDATED)
Boran Zhou, Hui Yang, Ya-Hui Zhang

The standard theoretical framework for fractional quantum anomalous Hall effect (FQAH) assumes an isolated flat Chern band in the single particle level. In this paper we challenges this paradigm for the FQAH recently observed in the pentalayer rhombohedral stacked graphene aligned with hexagon boron nitride (hBN). We show that the external moir\'e superlattice potential is simply a perturbation in a model with continuous translation symmetry. Through Hartree Fock calculation, we find that interaction opens a sizable remote band gap, resulting an isolated narrow $C=1$ Chern band at filling $\nu=1$. From exact diagonalization (ED) we identify FQAH phases at various fillings. But they exist also in the calculations without any external moir\'e potential. We suggest that the QAH insulator at $\nu=1$ should be viewed as an interaction driven QAH-Wigner crystal, which is then pinned by a small moir\'e potential. In the second part we propose a new setup with Coulomb generated moir\'e superlattice. For example, we separate $n$-layer graphene and twisted bilayer graphene (TBG) with a thin hBN and imprint the superlattice of the TBG to the $n$-layer graphene. Now the superlattice potential is controlled by the thickness $d$ of the hBN and the superlattice period is controlled by the twist angle of the TBG. Overall in both setups the $C=1$ QAH-Wigner crystal is robust with a crystal period around $10\mathrm{nm}$ in 4-layer, 5-layer, 6-layer and 7-layer graphene systems. Our work suggests a new direction to explore the interplay of topology and FQAH with spontaneous Wigner crystal formation in the vanishing moir\'e potential limit.


Electronic interactions in Dirac fluids visualized by nano-terahertz spacetime mapping. (arXiv:2311.11502v2 [cond-mat.str-el] UPDATED)
Suheng Xu, Yutao Li, Rocco A. Vitalone, Ran Jing, Aaron J. Sternbach, Shuai Zhang, Julian Ingham, Milan Delor, James. W. McIver, Matthew Yankowitz, Raquel Queiroz, Andrew J. Millis, Michael M. Fogler, Cory R. Dean, James Hone, Mengkun Liu, D.N. Basov

Ultraclean graphene at charge neutrality hosts a quantum critical Dirac fluid of interacting electrons and holes. Interactions profoundly affect the charge dynamics of graphene, which is encoded in the properties of its collective modes: surface plasmon polaritons (SPPs). The group velocity and lifetime of SPPs have a direct correspondence with the reactive and dissipative parts of the tera-Hertz (THz) conductivity of the Dirac fluid. We succeeded in tracking the propagation of SPPs over sub-micron distances at femto-second (fs) time scales. Our experiments uncovered prominent departures from the predictions of the conventional Fermi-liquid theory. The deviations are particularly strong when the densities of electrons and holes are approximately equal. Our imaging methodology can be used to probe the electromagnetics of quantum materials other than graphene in order to provide fs-scale diagnostics under near-equilibrium conditions.


Tilted Dirac superconductor at quantum criticality: Restoration of Lorentz symmetry. (arXiv:2311.12797v2 [cond-mat.supr-con] UPDATED)
Pablo Reiser, Vladimir Juricic

Lorentz symmetry appears as a quite robust feature of the strongly interacting Dirac materials even though the lattice interactions break such a symmetry. We here demonstrate that the Lorentz symmetry is restored at the quantum-critical point (QCP) separating the tilted Dirac semimetal, breaking this symmetry already at the noninteracting level, from a gapped $s-$wave superconducting instability. To this end, we employ a one-loop $\epsilon=(3-D)-$expansion close to the $D=3$ upper critical dimension of the corresponding Gross-Neveu-Yukawa field theory. In particular, we show that the tilt parameter is irrelevant and ultimately vanishes at the QCP separating the two phases. In fact, as we argue here, such a Lorentz symmetry restoration may be generic for the strongly interacting tilted Dirac semimetals, irrespective of whether they feature mirror-symmetric or mirror-asymmetric tilting, and is also insensitive to whether the instability represents an insulator or a gapped superconductor. The proposed scenario can be tested in the quantum Monte Carlo simulations of the interacting tilted Dirac fermion lattice models.


Non-equilibrium dynamics of topological defects in the 3d O(2) model. (arXiv:2311.13074v1 [hep-lat] CROSS LISTED)
Edgar López-Contreras, Jaime Fabián Nieto Castellanos, Elías Natanael Polanco-Euán, Wolfgang Bietenholz

We present a study of the 3d O(2) non-linear $\sigma$-model on the lattice, which exhibits topological defects in the form of vortices. They tend to organize into vortex lines that bear close analogies with global cosmic strings. Therefore, this model serves as a testbed for studying the dynamics of topological defects. It undergoes a second order phase transition, hence it is appropriate for investigating the Kibble-Zurek mechanism. In this regard, we explore the persistence of topological defects when the temperature is rapidly reduced from above to below the critical temperature; this cooling (or "quenching") process takes the system out of equilibrium. We probe a wide range of inverse cooling rates $\tau_{\rm Q}$ and final temperatures, employing distinct Monte Carlo algorithms. The results consistently show that the density of persisting topological defects follows a power-law in $\tau_{\rm Q}$, in agreement with Zurek's conjecture. On the other hand, at this point our results do not confirm Zurek's prediction for the exponent in this power-law, but its final test is still under investigation.


Found 1 papers in acs-nano
Date of feed: Sun, 26 Nov 2023 14:12:36 GMT

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[ASAP] Molybdenum Chloride Nanostructures with Giant Lattice Distortions Intercalated into Bilayer Graphene
Qiunan Liu, Yung-Chang Lin, Silvan Kretschmer, Mahdi Ghorbani-Asl, Pablo Solís-Fernández, Ming-Deng Siao, Po-Wen Chiu, Hiroki Ago, Arkady V. Krasheninnikov, and Kazu Suenaga

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ACS Nano
DOI: 10.1021/acsnano.3c06958

Found 3 papers in comm-phys


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Topological and high-performance nonreciprocal extraordinary optical transmission from a guided mode to free-space radiation
Kosmas L. Tsakmakidis

Communications Physics, Published online: 24 November 2023; doi:10.1038/s42005-023-01462-z

This paper theoretically predicts near-unity efficiency in converting a guided mode to free space radiation via a deep-subwavelength metallic hole. This phenomenon is enabled by a topologically protected one-way waveguide mode, where reciprocity is broken through an external magnetic field at terahertz frequencies.

Author Correction: Spontaneous superconducting diode effect in non-magnetic Nb/Ru/Sr2RuO4 topological junctions
Yoshiteru Maeno

Communications Physics, Published online: 22 November 2023; doi:10.1038/s42005-023-01448-x

Author Correction: Spontaneous superconducting diode effect in non-magnetic Nb/Ru/Sr2RuO4 topological junctions

Breakdown of conventional winding number calculation in one-dimensional lattices with interactions beyond nearest neighbors
Jihong Ma

Communications Physics, Published online: 21 November 2023; doi:10.1038/s42005-023-01461-0

Topological insulators are bulk insulators with conducting zero-energy edge states conventionally predicted by topological indices, such as winding numbers in one-dimensional lattices. Here, the authors use the Jackiw-Rebbi theory to reveal that the number of topologically protected zero-energy states can be higher than the winding number.