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Based on the quantum valley Hall effect analogy, this work proposes a phononic crystal plate with ligament-type beams to obtain the topological valley transmission of elastic waves. A pure Bragg degenerate state appears in the high-frequency region with a resonator introduced. By rotating the central scatterer and the beams, the mirror symmetry is broken to form a topological bandgap. Subsequently, this work finds that two selective edge states also appear beside the commonly non-trivial crossing edge states in the topological bandgap by calculating the projected band and eigenvalue spectrum of the supercell with different valley Hall phases phononic crystals. Their appearance is due to band separation of the topological edge states caused by an increase in the rotation angle. Both selective edge states can transmit topologically in specific paths. They will help further to broaden the width of the frequency band of topological transmission. Besides, an elastic wave splitter is designed and demonstrated numerically, which can form two channels and three channels in different frequency bands. With the topological selective edge state disappearing, a topological corner state exists in the edge bandgap. This work provides a theoretical reference for practical applications of broadband elastic wave topological transmission and elastic energy trapping. [ABSTRACT FROM AUTHOR]

Fullerene-assembled low-dimensional materials have been experimentally realized in polymorphic forms and have attracted significant interest very recently. Here, we predict a two-dimensional (2D) honeycomb lattice material TM2(C60)3 (TM = Cr, Mo, and W) assembled from exohedral metallofullerene clusters TM(C60)3 that could exhibit planar triangular geometries. According to first-principles calculations combined with Monte Carlo simulations, we suggest that these 2D assembled materials exhibit various exotic physical properties, including ferromagnetism, ferroelectricity, and quantum anomalous Hall effect. Interestingly, mechanical strains could effectively tune their magnetic moments and switch the conducting spin channel of the Dirac bands at the Fermi level. Our work provides a new cluster-assembly design strategy toward cluster-assembled 2D materials based on fullerene characters. [ABSTRACT FROM AUTHOR]

Hole mobility anisotropy in 4H-SiC was investigated based on both experimental and theoretical approaches. First, the authors established a complete database of the anisotropic hole mobility along both directions parallel and perpendicular to the c -axis in 4H-SiC over the wide acceptor density and temperature ranges by preparing Hall bar structures on p-type SiC(11 2 ¯ 0) epitaxial layers. Empirical equations for the mobility along each direction vs the acceptor density and temperature were determined, which should be useful for the simulation and designing of any SiC devices. In addition to that, the anisotropy in the hole mobility was extracted from the experimental results, and its origin was discussed focusing on that in the effective mass (m ∗) of holes. The obtained mobility ratio was far from the m ∗ ratio at the valence band maximum, and an averaged m ∗ along each direction was determined by theoretical calculation taking into account the energy distribution of holes. Consequently, the authors revealed that the anisotropic hole mobility is explained quantitatively by the anisotropic m ∗ considering the E – k dispersion over the entire first Brillouin zone. [ABSTRACT FROM AUTHOR]

The body–boundary correspondence refers to the relationship between the body and boundary states of topological insulators (TIs). In TIs, the presence of boundary states is connected to the bulk topological properties of the material. The topology can be identified by studying the energy of the topological modes within the bulk bandgap. However, not all topological materials exhibit boundary states within the insulating energy gap. In many cases, the presence of boundary states can be hidden or masked by the bulk energy bands, making it difficult to measure TIs. Recent experiments have shown that defects, which are commonly found in crystalline materials, can be used as probes to explore higher-order topologies that have been recently realized on various platforms. These defects can generate fractional charges and stable bound states in the dispersion region, allowing us to observe the clear body–disclination correspondence. We have performed simulations using a coupled acoustic cavity system with C3 and C5 symmetries to investigate the body–disclination correspondence in topological crystal insulators (TCIs) in the field of acoustics. Simulation and theoretical results have demonstrated that defects such as disclinations can be used to probe higher-order topologies that were previously unobservable in three-dimensional structures. This approach allows us to detect fractional mode charges and stable bound states, which are crucial for understanding the topological nature of TCIs. Our work demonstrates the potential of using disclination defects to study the intricate relationship between the body and boundary states in topological materials, particularly in the context of acoustics. [ABSTRACT FROM AUTHOR]

Exploring the physics coupled with layer degrees of freedom in materials has become a hot topic in quantum layertronics. We propose a robust second-order topological insulator monolayer RuOHX (X = F, Cl, and Br), a two-dimensional ferromagnetic semiconductor with large valley polarization, capable of undergoing topological phase transition induced by strain effect. In the bilayer RuOHX, we achieve layer-polarized anomalous Hall effect through interlayer sliding, originating from layer-stacking Berry curvature. Moreover, it can be controlled and reversed by the direction of ferroelectric polarization. Under appropriate biaxial strain, the bilayer RuOHX exhibits quantum layer spin Hall effect in which the helical edge states are manifested as spin-chirality-locking, due to the degeneracy of layer-polarized quantum anomalous Hall effect. Our work explores the potential application via layer-stacking topological properties for future quantum device applications. [ABSTRACT FROM AUTHOR]

Topology is essential for achieving unchanged (or protected) quantum properties in the presence of perturbations. A challenge facing the application is the variable protection levels displayed in real systems associated with the reconstructive behaviors of the dissipationless modes. Despite various insights on potential causes of backscattering, the edge-state-based approach is incomplete because the bulk states also contribute indispensably. This study investigates sample-scale reconstruction where dissipationless modes are global objects instead of being restricted to the sample edge. An integer quantum Hall effect hosted in a Corbino geometry is adopted and brought to the verge of a breakdown. Two independent and simultaneous detections are performed to capture transport responses in both longitudinal and transverse directions. The real-time correspondence between orthogonal results confirms two facts. 1. Dissipationless modes undergo frequent reconstruction in response to electrochemical potential changes, causing dissipationless current paths to expand transversely into the bulk while preserving chirality. A breakdown only occurs when a backscattering emerges between reconstructed dissipationless current paths bridging opposite edge contacts. 2. Topological protection is subject to an interplay of disorder, electron-electron interaction, and topology. The proposed reconstruction mechanism qualitatively explains the robustness variations, beneficial for protection optimization. Understanding the mechanisms influencing the robustness of topologically protected states is of fundamental relevance. This experimental work demonstrates, through the observation of real-time longitudinal and transverse responses, the importance of transverse reconstruction of protected modes which is influenced by electron-electron interaction in addition to disorder. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) half-metallic magnets are expected to achieve breakthroughs in the field of spintronics and quantum computation due to their 100% spin polarization and non-dissipative ballistic transport characteristics. However, the current availability of practical applications for these materials is limited. In this paper, a new 2D material NiVS6As2 is predicted based on density functional theory (DFT). It has a ferromagnetic ground state with a high Curie temperature, TC = 150 K and half-semi-metal (HSM) band structure protected by a structural symmetry degeneracy point on the Fermi surface, which can be controlled by an electric field and strain. When an out-of-plane electric field is applied, NiVS6As2 shows a Chern insulator with a quantum anomalous Hall (QAH) effect. These results expand the family of 2D magnetic semimetals, and provide new theoretical inspiration for understanding the protection of degenerate point symmetry. [ABSTRACT FROM AUTHOR]

Quantum Hall systems are platforms of choice to study topological properties of condensed matter systems and anyonic exchange statistics. In this work we have developed a tunable radiofrequency edge magnetoplasmonic resonator controlled by both the magnetic field and a set of electrostatic gates, meant to serve as a versatile platform for future interferometric devices designed to evidence non-abelian anyons. In our device, gates allow us to change both the size of the resonant cavity and the electronic density of the two-dimensional electron gas. We show that we can continuously control the frequency response of our resonator, making it possible to develop an edge magnetoplasmon interferometer. As we reach smaller sizes of our resonator, finite size effects caused by the measurement probes manifest. In the future, such device will be a valuable tool to investigate the properties of non-abelian anyons in the fractional quantum Hall regime. Edge-magnetoplasmon interferometers have been proposed as a tool to investigate anyonic properties of quasiparticles in the regime of the Fractional Quantum Hall effect. In this work, the authors demonstrate the possibility to control electrostatically the resonance frequency of EMP resonators of micrometric size and explain the role of gates, paving the way toward the realization of anyonic interferometers. [ABSTRACT FROM AUTHOR]

The discovery of the quantum Hall effect has established the foundation of the field of topological condensed matter physics. An amazingly accurate quantization of the Hall conductance, now enshrined in quantum metrology, is stable against any reasonable perturbation due to its topological protection. Conversely, the latter implies a form of censorship by concealing any local information from the observer. The spatial distribution of the current in a quantum Hall system is such a piece of information, which, thanks to spectacular recent advances, has now become accessible to experimental probes. It is an old question whether the original and intuitively compelling theoretical picture of the current, flowing in a narrow channel along the sample edge, is the physically correct one. Motivated by recent experiments locally imaging quantized current in a Chern insulator (Bi, Sb)2Te3 heterostructure [Rosen et al., Phys. Rev. Lett. 129, 246602 (2022); Ferguson et al., Nat. Mater. 22, 1100-1105 (2023)], we theoretically demonstrate the possibility of a broad "edge state" generically meandering away from the sample boundary deep into the bulk. Further, we show that by varying experimental parameters one can continuously tune between the regimes with narrow edge states and meandering channels, all the way to the charge transport occurring primarily within the bulk. This accounts for various features observed in, and differing between, experiments. Overall, our findings underscore the robustness of topological condensed matter physics, but also unveil the phenomenological richness, hidden until recently by the topological censorship--most of which, we believe, remains to be discovered. [ABSTRACT FROM AUTHOR]

Abstract In this research article, the (1+1)- and (2+1)-dimensional Chiral nonlinear Schrödinger equations (CNLSEs) are studied, which play an important role in the development of quantum mechanics, particularly in the field of quantum Hall effect. Our primary goal is to obtain the analytical solutions utilizing novel methodology, particularly the modified extended tanh-function technique. We concentrate on the search to solitary wave solutions inside the (1+1)- and (2+1)-dimensional CNLSEs, which are relevant in domains such as optics, electro-magnetic wave propagation, plasma physics, optics and quantum mechanics. Our objective is to increase knowledge of this equation and give insight into the behavior of solitary waves by employing a novel mathematical technique. This will be accomplished by displaying our findings in 2D and 3D graphics. We believe that our results would pave a way for future research generating optical memories based on the nonlinear solitons.

The interplay between novel topological states and superconductivity has garnered substantial interest due to its potential for topological quantum computing. The Josephson effect serves as a useful probe for edge superconductivity in these hybrid topological materials. In Josephson junctions based on topological materials, supercurrents exhibit unique quantum interference patterns, including the conventional Fraunhofer oscillations, the Φ0-periodic oscillation, and the 2Φ0-periodic oscillation in response to the external magnetic field (Φ0 = h/2e is the flux quantum, h the Planck constant, and e the electron charge). These interference patterns stem from varied Andreev reflection mechanisms and the associated current density profiles. This review seeks to comprehensively examine the theoretical and experimental advancements in understanding the quantum interference patterns of edge supercurrents in Josephson junctions based on quantum spin Hall, quantum Hall, and quantum anomalous Hall systems. [ABSTRACT FROM AUTHOR]

Magnetic skyrmion is a promising information carrier for its low critical driven current density, topological stability, and small size, which has been proposed for various devices such as racetrack memory and logic gates. However, the skyrmion Hall effect originating from Magnus force leads to transverse motion, which hinders the development of skyrmionic device applications. Here, we propose artificial tracks built by standing surface acoustic waves (SSAWs) to suppress the skyrmion Hall effect through micromagnetic simulations. We systematically study the dynamics of an isolated skyrmion under SSAWs and driven currents in a prototype of the ferromagnetic skyrmion system. The skyrmion Hall angle changes from 80° to 0°, where the skyrmion motion is along the driven current. An analytical model considering magnetoelastic energy induced by SSAWs is developed, and a linear relation between the current density and the critical SSAW amplitude to eliminate the skyrmion Hall effect is achieved. Furthermore, a reconfigurable multichannel skyrmion racetrack is constructed through the change of SSAW wavelengths. Our work opens a feasible route for the suppression of skyrmion Hall effect via SSAWs. [ABSTRACT FROM AUTHOR]

In recent years, the skyrmion lattice phase with a short lattice constant has attracted attention due to its high skyrmion density, making it a promising option for achieving high-density storage memory and for observing novel phenomena like the quantized topological Hall effect. Unlike conventional non-centrosymmetric systems where the Dzyaloshinsky–Moriya interaction plays a crucial role, the short pitch skyrmion phase requires a quadratic magnetic interaction J (q) with a peak at finite- Q , and weak easy-axis magnetic anisotropy is also critical. Thus, conducting first-principles evaluations is essential for understanding the formation mechanism as well as for promoting the discovery of new skyrmion materials. In this Perspective, we focus on recent developments of the first-principles evaluations of these properties and apply them to the prototype systems Gd T 2 X 2 and Eu T 2 X 2 , where T denotes a transition metal and X represents Si or Ge. In particular, based on the spin density functional theory with the Hubbard correction combined with the Liechtenstein method in the Wannier tight-binding model formalism, we first show that the Hubbard U and Hund's coupling is essential to stabilize a skyrmion lattice state by enhancing the easy-axis anisotropy. We then discuss mechanisms of finite- Q instability and show that competition among Gd-5 d orbitals determines whether ferromagnetism or a finite- Q structure is favored in Gd T 2 Si 2 with T = Fe and Ru. Our systematic calculations reveal that GdRu 2 X 2 , GdOs 2 X 2 , and GdRe 2 X 2 are promising, while GdAg 2 X 2 , GdAu 2 X 2 , and EuAg 2 X 2 are possible candidates as the skyrmion host materials. Analysis based on a spin spiral calculation for the candidate materials is also presented. [ABSTRACT FROM AUTHOR]

We report the growth, structural characterization, and transport properties of the quantum anomalous Hall insulator Vy(BixSb1−x)2−yTe3 (VBST) grown on a GaAs buffer layer by molecular beam epitaxy on a GaAs(111)A substrate. X-ray diffraction and transmission electron microscopy show that the implementation of a GaAs buffer layer improves the crystal and interface quality compared to the control sample grown directly on an InP substrate. Both samples exhibit the quantum anomalous Hall effect (QAHE), but, with similar thermal stability despite their different structural properties. Notably, the QAHE in the sample grown on a GaAs buffer layer displays a significantly larger (almost double) coercive field with a much smaller resistivity peak at magnetization reversal. Possible effects of the interface quality on the magnetic properties of VBST and the QAHE are discussed. [ABSTRACT FROM AUTHOR]

The interface and dielectric environment of graphene transistors are of great importance to commercial circuit integrations. The tangling bond in oxide‐based dielectric severely lagged the carrier mobility while the 2D dielectric layer (for instance, hexagonal boron nitride) unavoidably hastened complicated condensed physics even at room temperature. Herein, multilayer black phosphorus (BP) a versatile and widely‐tunable dielectric candidate for manifesting graphene fermions is demonstrated. Because of hetero‐interfacial charge redistributions, a vertical electric double‐layer between the bottom BP layer and top graphene spontaneously forms with the central BP layer as a soft barrier. Under dual‐gate modulation, abnormal step‐like evolution of Dirac fermions and charge‐transfer quantum Hall effect arises while the intrinsic Dirac behavior of graphene is preserved, ascribing to the gate‐tunable charge redistributions of dielectric BP layer. Moreover, the electric double‐layer transistors apply equally well to bilayer graphene with similar Dirac behavior but an enhanced interfacial charge interference. The findings not only create a new avenue to manipulate the fermions by assembling graphene with narrow‐gapped 2D layered materials but also promote electric double‐layer transistors as a new build block to design multifunctional devices. [ABSTRACT FROM AUTHOR]

[Display omitted] The conventional Hall effect is linearly proportional to the field component or magnetization component perpendicular to a film. Despite the increasing theoretical proposals on the Hall effect to the in-plane field or magnetization in various special systems induced by the Berry curvature, such an unconventional Hall effect has only been experimentally reported in Weyl semimetals and in a heterodimensional superlattice. Here, we report an unambiguous experimental observation of the antisymmetric planar Hall effect (APHE) with respect to the in-plane magnetic field in centrosymmetric rutile RuO 2 and IrO 2 single-crystal films. The measured Hall resistivity is found to be linearly proportional to the component of the applied in-plane magnetic field along a particular crystal axis and to be independent of the current direction or temperature. Both the experimental observations and theoretical calculations confirm that the APHE in rutile oxide films is induced by the Lorentz force. Our findings can be generalized to ferromagnetic materials for the discovery of anomalous Hall effects and quantum anomalous Hall effects induced by in-plane magnetization. In addition to significantly expanding knowledge of the Hall effect, this work opens the door to explore new members in the Hall effect family. [ABSTRACT FROM AUTHOR]

We report the growth, structural characterization, and transport properties of the quantum anomalous Hall insulator Vy(BixSb1−x)2−yTe3 (VBST) grown on a GaAs buffer layer by molecular beam epitaxy on a GaAs(111)A substrate. X-ray diffraction and transmission electron microscopy show that the implementation of a GaAs buffer layer improves the crystal and interface quality compared to the control sample grown directly on an InP substrate. Both samples exhibit the quantum anomalous Hall effect (QAHE), but, with similar thermal stability despite their different structural properties. Notably, the QAHE in the sample grown on a GaAs buffer layer displays a significantly larger (almost double) coercive field with a much smaller resistivity peak at magnetization reversal. Possible effects of the interface quality on the magnetic properties of VBST and the QAHE are discussed. [ABSTRACT FROM AUTHOR]

Edge states of a topological insulator can be used to explore fundamental science emerging at the interface of low dimensionality and topology. Achieving a robust conductance quantization, however, has proven challenging for helical edge states. In this work, we show wide resistance plateaus in kink states—a manifestation of the quantum valley Hall effect in Bernal bilayer graphene—quantized to the predicted value at zero magnetic field. The plateau resistance has a very weak temperature dependence up to 50 kelvin and is flat within a dc bias window of tens of millivolts. We demonstrate the electrical operation of a topology-controlled switch with an on/off ratio of 200. These results demonstrate the robustness and tunability of the kink states and its promise in constructing electron quantum optics devices. [ABSTRACT FROM AUTHOR]

Studies of fractional quantum Hall effects (FQHE) across various two-dimensional electronic systems (2DES) have helped to establish the equilibrium FQHE many-body ground states with fractionally charged excitations and composite particles in condensed matter. Then, the question arises whether an FQHE system driven to non-equilibrium can approach a different stationary state from the known equilibrium FQHE states. To investigate this question, we examine FQHE over filling factors, ν, 2 ≥ ν ≥ 1 under non-equilibrium finite bias conditions realized with a supplementary dc-current bias, IDC, in high mobility GaAs/AlGaAs devices. Here, we show that all observable canonical equilibrium FQHE resistance minima at ∣IDC∣ = 0 undergo bimodal splitting vs. IDC, yielding branch-pairs and diamond shapes in color plots of the diagonal resistance, as canonical FQHE are replaced, with increasing IDC, by excited-state fractionally quantized Hall effects at branch intersections. A tunneling model serves to interpret the results. Equilibrium transport phenomena known as fractional quantum Hall effects (FQHE) have elucidated the quantum ground states of interacting many-body systems. This study of FQHE transport in the non-equilibrium context finds a bimodal dc-bias-induced splitting of canonical FQHE, a diamond pattern in the resistance minima trajectories vs. the magnetic field and the dc-bias, and excited-state FQHE. [ABSTRACT FROM AUTHOR]

The article discusses a new protocol for quantum secure direct communication (DI-QSDC) using hyper-entanglement, which ensures secure communication despite device imperfections. The protocol increases the capacity of the secure channel by utilizing hyper-encoding. The article also mentions the AAPPS-DACG Workshop, an international symposium on cosmology and particle astrophysics, and highlights the achievements of Chinese physicist Qi-Kun Xue. Xue has made significant contributions to condensed matter physics, particularly in the study of the quantum anomalous Hall effect (QAHE), and his work has led to advancements in understanding and applying quantum Hall states. Xue has received recognition and prestigious prizes for his achievements in the field of physics. [Extracted from the article]

In this paper, we propose a precise Wigner–Weyl calculus for the models defined on the honeycomb lattice. We construct two symbols of operators: the B symbol, which is similar to the one introduced by F. Buot, and the W (or, Weyl) symbol. The latter possesses the set of useful properties. These identities allow us to use it in physical applications. In particular, we derive topological expression for the Hall conductivity through the Wigner-transformed Green function. This expression may be used for the description of the systems with artificial honeycomb lattice, when magnetic flux through the lattice cell is of the order of elementary quantum of magnetic flux. It is worth mentioning that, in the present paper, we do not consider the effect of interactions. [ABSTRACT FROM AUTHOR]

The problem of the two-dimensional motion of a charged particle with constant mass in the presence of a uniform constant perpendicular magnetic field features in several undergraduate and graduate quantum physics textbooks. This problem is very important to studies of two-dimensional materials that manifest quantum Hall behavior, as evidenced by several major discoveries over the last few years. Many real experimental samples are more complicated due to the anisotropic mass of the electrons. In this work, we provide the exact solution to this problem by means of a clever scaling of coordinates. Calculations are done for a symmetric gauge of the magnetic field. This study allows a broad audience of students and teachers to understand the mathematical techniques that lead to the solution of this quantum problem. Editor's note: The behavior of an electron confined to move in two dimensions in the presence of a perpendicular magnetic field underlies the quantum Hall effect. This is also an analytically solvable problem, so it is valuable to quantum mechanics pedagogy. This paper reviews the solution and then shows a neat trick for solving the problem when the electron's effective mass is anisotropic, a situation that is fairly common in solid-state systems. [ABSTRACT FROM AUTHOR]

Electronic interferometers using the chiral, one-dimensional (1D) edge channels of the quantum Hall effect (QHE) can demonstrate a wealth of fundamental phenomena. The recent observation of phase jumps in a Fabry-Pérot (FP) interferometer revealed anyonic quasiparticle exchange statistics in the fractional QHE. When multiple integer edge channels are involved, FP interferometers have exhibited anomalous Aharonov-Bohm (AB) interference frequency doubling, suggesting putative pairing of electrons into 2 e quasiparticles. Here, we use a highly tunable graphene-based QHE FP interferometer to observe the connection between interference phase jumps and AB frequency doubling, unveiling how strong repulsive interaction between edge channels leads to the apparent pairing phenomena. By tuning electron density in-situ from filling factor ν < 2 to ν > 7 , we tune the interaction strength and observe periodic interference phase jumps leading to AB frequency doubling. Our observations demonstrate that the combination of repulsive interaction between the spin-split ν = 2 edge channels and charge quantization is sufficient to explain the frequency doubling, through a near-perfect charge screening between the localized and extended edge channels. Our results show that interferometers are sensitive probes of microscopic interactions and enable future experiments studying correlated electrons in 1D channels using density-tunable graphene. Previous measurements of interferometers based on quantum Hall (QH) edge channels have suggested potential electron pairing effects. Here, the authors investigate the coupling between QH edge channels in graphene Aharonov-Bohm (AB) interferometers, proposing a possible single-particle explanation for the apparent interference phase jumps and AB frequency doubling. [ABSTRACT FROM AUTHOR]

Recently, topological insulators (TIs) have regained extensive attention in spintronics due to their potential applications in new‐generation spintronic devices, following the discovery of the quantum Hall effect and quantum anomalous Hall effect, which introduce the topological concept. In this review, the exotic spin transport phenomena are explored in TIs. The review offers a concise overview of the fundamental principles of TIs, followed by an exploration of diverse fabrication methods for TI materials. Characterization techniques of the topological surface states are also presented. The review delves into the intriguing spin current transport phenomena, focusing on spin‐to‐charge and charge‐to‐spin conversions in TI/ferromagnet bilayers, respectively. The review culminates summarizing key insights and project future directions for research on spin transport phenomena in TIs, emphasizing practical implications. [ABSTRACT FROM AUTHOR]

The article discusses a high-capacity device-independent quantum secure direct communication protocol using hyper-entanglement. It explains that quantum secure direct communication (QSDC) is a method of transmitting information directly using quantum states, and device-independent (DI) protocols have been developed to ensure unconditional security despite imperfections in devices. The article also mentions the CosPA 2024 conference, which focused on astrophysics, cosmology, and gravitation, and highlights Qi-Kun Xue receiving the 2023 State Preeminent Science and Technology Award, China's top scientific honor. Academician Qi-Kun Xue, a professor at Tsinghua's Department of Physics and president of the Southern University of Science and Technology, has been awarded the 2023 State Preeminent Science and Technology Award, China's top scientific honor, for his contributions to scientific and technological innovation. He is the first Chinese national to win the Fritz London Memorial Prize and the Oliver E. Buckley Condensed Matter Physics Prize. Xue's research team has made significant advancements in condensed matter physics, including the experimental observation of the quantum anomalous Hall effect (QAHE). The QAHE is a quantum Hall effect that can occur without an external magnetic field and has led to the development of practical applications and the exploration of novel quantum phenomena. [Extracted from the article]

Quantum Hall effect, the quantized transport phenomenon of electrons under strong magnetic fields, remains one of the hottest research topics in condensed matter physics since its discovery in 2D electronic systems. Recently, as a great advance in the research of quantum Hall effects, the quantum Hall effect in 3D systems, despite its big challenge, has been achieved in the bulk ZrTe 5 and Cd 3 As 2 materials. Interestingly, Cd 3 As 2 is a Weyl semimetal, and quantum Hall effect is hosted by the Fermi arc states on opposite surfaces via the Weyl nodes of the bulk, and induced by the unique edge states on the boundaries of the opposite surfaces. However, such intriguing edge state distribution has not yet been experimentally observed. Here, we aim to reveal experimentally the unusual edge states of Fermi arcs in acoustic Weyl system with the aid of pseudo-magnetic field. Benefiting from the macroscopic nature of acoustic crystals, the pseudo-magnetic field is introduced by elaborately designed the gradient on-site energy, and the edge states of Fermi arcs on the boundaries of the opposite surfaces are unambiguously demonstrated in experiments. Our system serves as an ideal and highly tunable platform to explore the Hall physics in 3D system, and has the potential in the application of new acoustic devices. [ABSTRACT FROM AUTHOR]

Fractional quantum Hall (FQH) states are exotic quantum many-body phases whose elementary charged excitations are anyons obeying fractional braiding statistics. While most FQH states are believed to have Abelian anyons, the Moore–Read type states with even denominators – appearing at half filling of a Landau level (LL) – are predicted to possess non-Abelian excitations with appealing potential in topological quantum computation. These states, however, depend sensitively on the orbital contents of the single-particle LL wavefunctions and the LL mixing. Here we report magnetotransport measurements on Bernal-stacked trilayer graphene, whose multiband structure facilitates interlaced LL mixing, which can be controlled by external magnetic and displacement fields. We observe robust FQH states including even-denominator ones at filling factors ν = − 9/2, − 3/2, 3/2 and 9/2. In addition, we fine-tune the LL mixing and crossings to drive quantum phase transitions of these half-filling states and neighbouring odd-denominator ones, exhibiting related emerging and waning behaviour. The fractional quantum Hall effect offers a potential platform to harness non-Abelian anyons. Here, the authors report fractional quantum Hall states in trilayer graphene and drive quantum phase transitions between neighbouring states. [ABSTRACT FROM AUTHOR]

Kagome materials serve as crucial platforms for investigating the quantum anomalous Hall effect (QAHE) due to the presence of kagome bands in their electronic structures. However, despite the theoretical predictions being proposed, kagome band material realizations have been limited. In this work, through tight-binding (TB) model analysis, by setting the nearest-neighbor hopping integrals with opposite signs, we propose a Yin–Yang kagome band structure characterized by two stable enantiomorphic kagome bands. Furthermore, we design a monolayer V3Cl6 to confirm the TB model. Three V atoms are located in different coordination environments in V3Cl6, so opposite signs of the hopping integrals between two of their orthogonal d orbitals can be achieved, which is the key to realize Yin–Yang kagome band structures. The calculated band structures obtained from first principles are consistent with those from the TB model. Additionally, we find that the two enantiomorphic flat bands in monolayer V3Cl6 possess opposite Chern number after spin–orbit coupling is considered, which can also be confirmed from symmetry index analysis. The Chern numbers as well as the topological properties can be modulated by doping hole or adjusting the magnetization directions, so the QAHE can be tuned in monolayer V3Cl6. Our results provide a practicable pathway for realizing Yin–Yang kagome band structures and achieving tunable QAHE in them. [ABSTRACT FROM AUTHOR]

Transition-metal doped topological insulators have been widely explored since the observation of quantum anomalous Hall effect (QAHE). Subsequently, the magnetic (Pb,Sn)(Te,Se) was predicted to possibly possess a high-temperature QAHE state. However, the fundamental understanding of Cr-doping-induced ferromagnetism in this system remains unclear. Here, we report the stable ferromagnetism in the high-crystalline Cr-doped SnTe films. Upon Cr doping, the magnetoconductance unveils a crossover from weak antilocalization to weak localization. Further increasing the Cr concentration to Cr0.17Sn0.83Te introduces a strong ferromagnetism with a Curie temperature of ~140 K. We detected a sizable spin moment ms = 2.28 ± 0.23 μB/Cr and a suppressed orbital moment ml = 0.02 μB/Cr. Cr dopants prefer to substitute the Sn sites and behave as divalent cations, as indicated by the experimental results and density function theory calculations. The controllable growth of magnetic SnTe thin films provides enlightenment towards the high-temperature QAHE in magnetic TCIs for the desired dissipationless transport in electronics. [ABSTRACT FROM AUTHOR]

Kagome materials serve as crucial platforms for investigating the quantum anomalous Hall effect (QAHE) due to the presence of kagome bands in their electronic structures. However, despite the theoretical predictions being proposed, kagome band material realizations have been limited. In this work, through tight-binding (TB) model analysis, by setting the nearest-neighbor hopping integrals with opposite signs, we propose a Yin–Yang kagome band structure characterized by two stable enantiomorphic kagome bands. Furthermore, we design a monolayer V3Cl6 to confirm the TB model. Three V atoms are located in different coordination environments in V3Cl6, so opposite signs of the hopping integrals between two of their orthogonal d orbitals can be achieved, which is the key to realize Yin–Yang kagome band structures. The calculated band structures obtained from first principles are consistent with those from the TB model. Additionally, we find that the two enantiomorphic flat bands in monolayer V3Cl6 possess opposite Chern number after spin–orbit coupling is considered, which can also be confirmed from symmetry index analysis. The Chern numbers as well as the topological properties can be modulated by doping hole or adjusting the magnetization directions, so the QAHE can be tuned in monolayer V3Cl6. Our results provide a practicable pathway for realizing Yin–Yang kagome band structures and achieving tunable QAHE in them. [ABSTRACT FROM AUTHOR]

Introducing magnetism into topological insulators enables exotic phenomena such as quantum anomalous Hall effect. By fabricating van der Waals (vdW) heterostructures using layered magnetic materials, we can not only induce a gap in the non-magnetic topological surface states through magnetic proximity but also further manipulate the magnetic properties of magnetic topological insulators. However, the scarcity of 2D ferromagnetic insulator materials limits the fabrication of such heterostructures. Here, we demonstrate the vdW heterostructure devices comprising metal ferromagnetic Fe3GeTe2 nanoflakes and few-layer antiferromagnetic topological insulator MnBi2Te4 separated by an insulating hexagonal-boron nitride spacer. These devices exhibit significant exchange bias with the exchange bias field of over 100 mT under certain conditions. Our results prove that besides magnetic insulators, metallic magnets can also effectively adjust the magnetic properties of topological insulators, thereby inspiring diverse configurations of the heterostructures between topological insulators and magnetic materials. [ABSTRACT FROM AUTHOR]

Introducing magnetism into topological insulators enables exotic phenomena such as quantum anomalous Hall effect. By fabricating van der Waals (vdW) heterostructures using layered magnetic materials, we can not only induce a gap in the non-magnetic topological surface states through magnetic proximity but also further manipulate the magnetic properties of magnetic topological insulators. However, the scarcity of 2D ferromagnetic insulator materials limits the fabrication of such heterostructures. Here, we demonstrate the vdW heterostructure devices comprising metal ferromagnetic Fe3GeTe2 nanoflakes and few-layer antiferromagnetic topological insulator MnBi2Te4 separated by an insulating hexagonal-boron nitride spacer. These devices exhibit significant exchange bias with the exchange bias field of over 100 mT under certain conditions. Our results prove that besides magnetic insulators, metallic magnets can also effectively adjust the magnetic properties of topological insulators, thereby inspiring diverse configurations of the heterostructures between topological insulators and magnetic materials. [ABSTRACT FROM AUTHOR]

In graphene on transition metal dichalcogenides, two types of spin–orbit coupling (SOC)—Rashba and spin–valley Zeeman SOCs—can coexist that modify graphene's electronic band differently. Herein, it is shown that the Landau levels (LLs) are also affected by these SOCs distinctively enough to estimate their relative strengths from the Landau fan diagram. A simple theoretical model is used to calculate the LL spectra of graphene for different SOC strengths, revealing that when the total SOC is strong enough (i.e., when it is comparable to the half of the energy gap between the LLs of an intrinsic graphene), the corresponding LLs will split and cross with others depending sensitively on the relative strengths of the SOC terms. To demonstrate how one can use it to estimate the relative SOC strengths, the four key features that are well separated from the complex background are first identified and compared with experiment to show that in the sample investigated, the Rashba SOC is stronger than the spin–valley Zeeman SOC consistent with other spectroscopic measurements. The study therefore provides a simple and practical strategy to analyze the LL spectrum in graphene with SOC before carrying out more in‐depth measurements. [ABSTRACT FROM AUTHOR]

Ferrovalley materials are garnering significant interest for their potential roles in advancing information processing and enhancing data storage capabilities. This study utilizes first-principles calculations to determine that the Janus monolayer TiTeCl exhibits the properties of a ferrovalley semiconductor. This material demonstrates valley polarization with a notable valley splitting of 80 meV. Additionally, the Berry curvature has been computed across the first Brillouin zone of the monolayer TiTeCl. The research also highlights that topological phase transitions ranging from ferrovalley and half-valley metals to quantum anomalous Hall effect states can occur in monolayer TiTeCl under compressive strains ranging from −1% to 0%. Throughout these strain changes, monolayer TiTeCl maintains its ferromagnetic coupling. These characteristics make monolayer TiTeCl a promising candidate for the development of new valleytronic and topological devices. [ABSTRACT FROM AUTHOR]

The long-term goal of our study is to perform a simulation on a rapidly rotating gas of ultracold bosonic atoms. When the rotation frequency is close to the harmonic trap frequency, the trapping force is compensated by the centrifugal force and only the Coriolis force remains, analogous to the Lorentz force. The quantum Hall effect regime is reached when the number of vortices is larger than the number of atoms. In this work, we demonstrate a variety of excitations of the fractional quantum Hall states of composite fermions and ultracold two-dimensional rapidly rotating bosonic atoms. Second, we can also check directly whether there is a relationship between these two phenomena by calculating the energy of N = 8 bosons in the ground state of the harmonic oscillator and a few-boson elementary excitations for the Bose–Laughlin state at the half filling factor. [ABSTRACT FROM AUTHOR]

We prove several results for the Coulomb gas in any dimension d≥2$d \ge 2$ that follow from isotropic averaging, a transport method based on Newton's theorem. First, we prove a high‐density Jancovici–Lebowitz–Manificat law, extending the microscopic density bounds of Armstrong and Serfaty and establishing strictly sub‐Gaussian tails for charge excess in dimension 2. The existence of microscopic limiting point processes is proved at the edge of the droplet. Next, we prove optimal upper bounds on the k$k$‐point correlation function for merging points, including a Wegner estimate for the Coulomb gas for k=1$k=1$. We prove the tightness of the properly rescaled k$k$th minimal particle gap, identifying the correct order in d=2$d=2$ and a three term expansion in d≥3$d \ge 3$, as well as upper and lower tail estimates. In particular, we extend the two‐dimensional "perfect‐freezing regime" identified by Ameur and Romero to higher dimensions. Finally, we give positive charge discrepancy bounds which are state of the art near the droplet boundary and prove incompressibility of Laughlin states in the fractional quantum Hall effect, starting at large microscopic scales. Using rigidity for fluctuations of smooth linear statistics, we show how to upgrade positive discrepancy bounds to estimates on the absolute discrepancy in certain regions. [ABSTRACT FROM AUTHOR]

The groundbreaking discovery of high-order topological insulators has opened the avenues for exploring complex topological states, especially the corner states. Typically, corner states undergo hybridization because of point-group symmetry, leading to degeneracy that has yet to be thoroughly investigated in the realm of higher-order topological states. In this study, we introduce a straightforward yet effective photonic crystal design that facilitates the realization of robust photonic corner states and their intricate hybridization. We reveal that, in addition to the conventional point-group symmetry, the local sublattice symmetry also plays a pivotal role in protecting the corner states. By strategically disrupting the sublattice symmetry, we introduce a tunable mechanism for controlling the hybridization of corner states within our proposed photonic structure. This research sheds light on the symmetrical protection mechanisms of topological corner states in photonic crystals, paving the way for innovative designs of photonic devices leveraging the unique properties of zero-dimensional corner states. [ABSTRACT FROM AUTHOR]

In the recent years, the thermal Hall transport has risen as an important diagnosis of the physical properties of the elementary excitations in various quantum materials, especially among the Mott insulating systems where the electronic transports are often featureless. Here we review the recent development of thermal Hall effects in quantum magnets where all the relevant excitations are charge-neutral. In addition to summarizing the existing experiments, we pay a special attention to the underlying mechanisms of the thermal Hall effects in various magnetic systems, and clarify the connection between the microscopic physical variables and the emergent degrees of freedom in different quantum phases. The external magnetic field is shown to modify the intrinsic Berry curvature properties of various emergent and/or exotic quasiparticle excitations in distinct fashions for different quantum systems and quantum phases, contributing to the thermal Hall transports. These include, for example, the conventional ones like the magnons in ordered magnets, the triplons in dimerized magnets, the exotic and fractionalized quasiparticles such as the spinons and the magnetic monopoles in quantum spin liquids. We review their contribution and discuss their presence in the thermal Hall conductivity in different physical contexts. We expect this review to provide a useful guidance for the physical mechanism of the thermal Hall transports in quantum magnets. [ABSTRACT FROM AUTHOR]

The multifrequency quantum valley Hall effect (QVHE) has been realized to significantly improve the transmission capacity of topological waveguides, and the multimode QVHE with a large valley Chern number has been realized to increase the mode density of topological waveguides. However, multifrequency and multimode QVHEs have not been realized simultaneously. In this work, using tight‐binding model calculations and numerical simulations, a valley photonic crystal (VPC) consisting of a Stampfli‐triangle photonic crystal is constructed, and its multiple degeneracies in the low‐frequency and high‐frequency bands split simultaneously to realize the QVHE with multiple topological edge states (TESs). The multifrequency and multimode topological transmission with two low‐frequency modes and four high‐frequency modes is realized by means of simulations and experiments through a Z‐shaped waveguide constructed using two VPCs with opposite valley Chern numbers to prove the realization of a large valley Chern number in the two frequency bands. The two low‐frequency modes are successfully distinguished with position‐dependent selective excitations, which experimentally demonstrate the occurrence of a large valley Chern number. A frequency‐dependent multimode beam splitter is theoretically proposed for high‐performance integrated photonic device applications. These results provide new ideas for high‐efficiency and high‐capacity optical transmission and communication devices and their integration; furthermore, they broaden the application range of TESs. [ABSTRACT FROM AUTHOR]

Plateau–plateau transition in the integer quantum Hall effect is a phase transition between metal and insulator. The behavior describing how the width Δ B of the transition changes with temperature and frequency of radiations imposed has been explored extensively. It decreases with the decrease of temperature and frequency, but saturates at a critical temperature or frequency. We have recently discussed the effect of axion dark matter on the saturation. The axion generates radiations under a strong magnetic field in the experiment of the quantum Hall effect. The radiations play a similar role to that of radiations imposed externally. In this paper we discuss in detail how the width behaves in relation to temperature and frequency under the effect of axion dark matter. We show that the axion effect can be observable in low temperatures roughly below 100 mK. According to our detailed analysis of the saturation, we find that the critical frequency of saturation observed in the previous experiment strongly suggests axion mass ma = (0.95∼0.99) × 10−5 eV. [ABSTRACT FROM AUTHOR]

A step-by-step description of the technique for manufacturing various van der Waals heterostructures is provided. First, the procedure to obtain monolayer and few-layer flakes from layered materials, in particular graphite and hexagonal boron nitride, is discussed. Next, different approaches to their assembly depending on the required final structure are considered. Finally, the procedure for making ohmic contacts is described in detail and the parameters for plasma chemistry and metal deposition are given. The field effect is discovered in transport measurements carried out at various temperatures, but a number of features, such as a strong shift of the charge neutral point from the zero-gate voltage, a large resistance away from the charge neutral point, and a low mobility, indicate a poor quality of the resulting devices. Nevertheless, one of the fabricated devices demonstrates good quality: the maximum mobility is estimated as 15 000 cm2/(V s), and the magnetic field dependences demonstrate the quantum Hall effect that is standard for high-quality graphene. Unexpectedly, scanning electron microscope images of the resulting devices reveal a large amount of contamination on the surface of the flakes, which may explain the corresponding quality of our devices. Preliminary results of flakes cleaning with chemical compounds and thermal treatment are presented. [ABSTRACT FROM AUTHOR]

The article in the journal "Applied Physics Letters" discusses the emerging field of topological and chiral matter, which encompasses various disciplines such as condensed matter physics, materials science, and engineering. It explores the properties and potential applications of topological insulators, Dirac and Weyl semimetals, and chiral nanostructures. The document highlights theoretical and computational contributions, indicating that experimental research in this area is still in its early stages. The Special Topic issue aims to deepen the understanding of these materials and guide the search for new ones, offering valuable insights for graduate students and researchers in academia. [Extracted from the article]

Topological insulators (TIs) are a new type of quantum state materials. Due to their novel physical properties, such as topological protection defect immunity to edge states, TIs have become the focus of attention in condensed matter and material physics. At present, the research on TIs has been gradually extended to classical wave fields such as electromagnetic waves, acoustic waves, and elastic waves, and has aroused extensive research interest. However, for elastic wave systems, most TIs cannot actively control topological interface states due to the limitation of fixed structure, which hinders their application in practical situations. Here, we propose a kind of tunable three-dimensional (3D) valley Hall insulator composed of magnetoelastic materials. First, the topological phase transition can be induced by the asymmetric geometry. Then, the working frequency of topological interface states can be changed by using static magnetic fields. Second, topological phase transformation can also be induced by independently tuning the distribution of static magnetic fields or pre-stress in each unit. Based on this, reconfigurable propagation routes of interface states with arbitrary shapes can be realized by tuning the distribution of static magnetic fields or pre-stress in each unit. Finally, considering the sandwich structure composed of different magnetic fields or pre-stress distribution modes, the waveguide with tunable width and route is designed by coupling edge and bulk states, which is convenient for application and better energy transfer. This study provides a reference for the design of a tunable intelligent elastic waveguide. [ABSTRACT FROM AUTHOR]

We report the effect of remote surface optical (RSO) phonon scattering on carrier mobility in monolayer graphene gated by ferroelectric oxide. We fabricate monolayer graphene transistors back-gated by epitaxial (001) Ba0.6Sr0.4TiO3 films, with field effect mobility up to 23 000 cm2 V−1 s−1 achieved. Switching ferroelectric polarization induces nonvolatile modulation of resistance and quantum Hall effect in graphene at low temperatures. Ellipsometry spectroscopy studies reveal four pairs of optical phonon modes in Ba0.6Sr0.4TiO3, from which we extract RSO phonon frequencies. The temperature dependence of resistivity in graphene can be well accounted for by considering the scattering from the intrinsic longitudinal acoustic phonon and the RSO phonon, with the latter dominated by the mode at 35.8 meV. Our study reveals the room temperature mobility limit of ferroelectric-gated graphene transistors imposed by RSO phonon scattering. [ABSTRACT FROM AUTHOR]

Based on the analogy of the quantum valley Hall effect, a ligament-type phononic crystal plate with local resonators is designed in this study to facilitate the valley state transport of low-frequency elastic waves. We analyze the key factors affecting the local resonance modes and reduce the frequency of the Dirac cone by changing the connection form of the structure's beams. The spatial inversion symmetry of the structure is broken to open a new band gap by introducing a mass difference in the resonator pair. The robustness of the designed structure's topological valley waveguide under defects and bends is verified. Based on this characteristic, we introduce the gradient heights into the supercell structure where elastic waves at different frequencies split and stop significantly on the supercell structure to achieve sub-wavelength topological rainbow trapping. This design provides a theoretical reference for exploring the low-frequency elastic topological mode and the application of topological rainbow capture in sub-wavelength structures. [ABSTRACT FROM AUTHOR]

Quantum anomalous Hall (QAH) insulators are an ideal platform for developing topological electronic devices, but their low observation temperature limits the applications. In this study, based on first-principles calculations, monolayer Ti2Sb2KRb and Ti2Bi2NaK are demonstrated to be QAH insulators with topological gaps 43 and 57 meV, respectively. Their Chern numbers are calculated to be C = − 2. The study of electronic structures indicates that the ferromagnetic topological property is induced by the energy band inversion of d xy and d x 2 − y 2 orbitals for Ti atoms near the Dirac cone. Both monolayer Ti2Sb2KRb and Ti2Bi2NaK exhibit a perpendicular magnetic anisotropy, and their Curie temperatures are estimated to be 480 and 478 K, respectively. The ferromagnetic coupling is induced by the small crystal-field splitting energy caused by Sb and Bi atom's large radius. Our study suggests that monolayer Ti2Sb2KRb and Ti2Bi2NaK are promising candidates for room temperature QAH insulators. [ABSTRACT FROM AUTHOR]

We report on transport characteristics of field effect two-dimensional electron gases (2DEGs) in 24 nm wide indium arsenide surface quantum wells. High quality single-subband magnetotransport with clear quantized integer quantum Hall plateaus is observed to filling factor ν = 2 in magnetic fields of up to B = 18 T, at electron densities up to 8 × 10 11 /cm2. Peak mobility is 11 000 cm2/Vs at 2 × 10 12 /cm2. Large Rashba spin–orbit coefficients up to 124 meV Å are obtained through weak anti-localization measurements. Proximitized superconductivity is demonstrated in Nb-based superconductor-normal-superconductor (SNS) junctions, yielding 78%–99% interface transparencies from superconducting contacts fabricated ex situ (post-growth), using two commonly used experimental techniques for measuring transparencies. These transparencies are on a par with those reported for epitaxially grown superconductors. These SNS junctions show characteristic voltages I c R n up to 870 μV and critical current densities up to 9.6 μA/μm, among the largest values reported for Nb-InAs SNS devices. [ABSTRACT FROM AUTHOR]