We study theoretical models for charge reflectometry and capacitive readout of the Majorana parity degree of freedom in Majorana box qubits, considering decoherence channels within the framework of the Lindblad master equation. Noting that a parity-dependent dynamical susceptibility ${\chi }_z\left(\omega \right)$ governs both readout schemes, we provide a general expression for ${\chi }_z\left(\omega \right)$ which covers the full crossover from the resonant regime to the off-resonant dispersive regime. In addition, we reexamine previous results which were obtained under a semiclassical factorization assumption. Using three different error measures, we show that this approximation is quantitatively justified in the dispersive regime. In the resonant regime, however, we find deviations from exact reference data, obtained by numerical solution for the steady state of the full Lindblad equation. These deviations are typically of the order of a few percent in the considered error measures.

We report the growth and physical properties of single-crystalline $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{a}}_3{\mathrm{S}}_6$ crystallizing in the $P{6}_3/mcm$ space group, which comprises alternating Ta-S layers and Bi layers with each Bi atom connected to adjacent S atoms. Temperature-dependent electrical resistivity measurements reveal a superconducting transition at 0.84 K, with an upper critical field of 231 Oe under an out-of-plane magnetic field. Magnetization measurements confirm its nature as a type-II superconductor, with anisotropic Ginzburg-Landau parameters ${\kappa }_{ab}=7.67$ and ${\kappa }_c=4.50$. Hall measurements reveal holes as the dominant species of charge carriers at room temperature. Hydrostatic pressure is applied, under which both the superconducting transition temperature and upper critical field increase sharply under low pressure before undergoing slight suppression under higher pressure. DFT calculations reveal nontrivial topological surface states on the (100) surface in $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{a}}_3{\mathrm{S}}_6$, which may offer a new avenue for exploring potential topological superconductivity in layered transition metal dichalcogenides.

Iron chalcogenides exhibit rich phenomena which are governed by orbital-dependent electronic interactions and strong electronic correlation. In particular, many studies have explored orbital selectivity in FeTe through Se doping. Here, applying tensile strain to thin films allows us to precisely control the system without other impurities that may arise from chemical doping to investigate the emergent behaviors in FeTe. Using angle-resolved photoemission spectroscopy, we observe a spectral weight transfer between $d_{\mathrm{xy}}$ and $d_{{\mathrm{z}}^2}$ orbitals, evidence of an orbital-selective Mott phase (OSMP). Beyond OSMP, we reveal an unobserved strain-induced effects, distinct from chemical doping. The evolution of $d_{\mathrm{xz}}$ orbital demonstrates how electron hopping mechanism plays an important role in defining the electronic properties of the system. Our findings highlight a direct correlation between epitaxial strain and the evolution of electronic structures in FeTe.

We develop a general theoretical framework showing that Berry curvature of electronic bands can produce intrinsic optical bistability under circularly polarized illumination. The bistability arises directly from Maxwell's boundary conditions, which couple the transmitted circular field to a transverse current generated by the imaginary component of the incident field. This transverse response is governed by anomalous Hall conductivities originating from the Berry curvature. By combining these components, we obtain a self-consistent nonlinear input-output equation that has multiple stable transmission states, demonstrating that bistability can emerge solely from the material's Berry curvature, without relying on cavities, interference paths, or external feedback mechanisms.

The discovery of higher-order topological phases hosting boundary modes at hinges or corners has revolutionized our understanding of quantum materials. While axion insulators (AXIs) characterized by symmetry indicator ${\mathbb{Z}}_4=2$ are known to host chiral hinge states, the topological landscape of magnetic crystals with a trivial indicator ${\mathbb{Z}}_4=0$ remains largely unexplored. In this work, we demonstrate that a trivial symmetry indicator can mask a rich variety of topological phases, including Weyl semimetals with even pairs of Weyl points, trivial insulators, and weak second-order topological insulators (WSOTIs). We find that these WSOTIs are rooted in fragile topology and support robust chiral hinge states that mimic the signatures of AXIs, despite their distinct topological invariants and contrasting spin-polarization patterns. Through Wilson loops analysis and symmetry-compatible orbital coupling, we establish a generalized bulk-hinge correspondence for WSOTIs and demonstrate that external magnetic fields and surface engineering can precisely control the propagation of their hinge states. Finally, we propose a WSOTI-AXI heterostructure that functions as a tunable topological spin splitter. Our results provide a general framework for uncovering higher-order topology in fragile phases and suggest a platform for topological transport of spin polarization.

We present a semilocal parametrization of the kinetic-energy density enhancement factor and the associated Pauli potential derived from jellium-slab calculations, within the context of orbital-free density functional theory (OF-DFT). The parametrization is constructed directly from analytical results for slab model systems and exact-exchange Kohn-Sham calculations and is designed to simultaneously satisfy a set of exact constraints, including the correct behavior in both the three-dimensional ($3D$) bulk limit and the two-dimensional ($2D$) extreme quantum limit. In particular, our parametrization reproduces the exact constant value of the Pauli contribution to the noninteracting kinetic energy when only a single slab discrete level is occupied and successfully describes the full dimensional crossover of the noninteracting kinetic energy from the $3D$ bulk limit to the $2D$ extreme quantum limit. The associated orbital-free Pauli potential accurately captures the evolution of surface-induced Friedel oscillations near the bulk-vacuum interface. To our knowledge, this represents the first semilocal kinetic-energy functional and Pauli potential parametrized on the basis of explicit first-principles calculations, with the kinetic-energy density properly capturing the challenging $3D\to 2D$ dimensional crossover.

Superionic crystal possesses a crystalline sublattice and diffusive ions, which is therefore assumed to be a thermal insulator while an electrical conductor, i.e., an ideal thermoelectric. Indeed, some of them, such as ${\mathrm{Cu}}_2\mathrm{Se}$, show excellent thermoelectric performance, while some superionic crystals, such as ${\mathrm{Ag}}_2\mathrm{Te}$, only possess a modest thermoelectric performance. In this work, we demonstrate that the thermoelectric performance of superionic crystals is significantly affected by the Soret effect, which originates from the local enthalpy mismatch between cations and anions. Our results show that the negative Soret effect transport coefficient, characterized by antialigned heat and enthalpy currents as shown in ${\mathrm{Cu}}_2\mathrm{Se}$, hinders the energy transfer channels of both conduction and mass diffusion, while the positive Soret effect transport coefficient with aligned heat and enthalpy currents as observed in ${\mathrm{Ag}}_2\mathrm{Te}$, promotes both these energy transfer channels. Meanwhile, the Soret effect in superionic crystals generates the ionic Seebeck effect. The ionic Seebeck coefficient stemming from the Soret effect can be considerable. The thermoelectric performance of a material is inversely (directly) proportional to the energy transfer coefficient (the Seebeck coefficient). Therefore, while superionic crystals possess the same crystalline structures, their thermoelectric performance may vary significantly, e.g., the figure of merit of ${\mathrm{Cu}}_2\mathrm{Se}$ and ${\mathrm{Ag}}_2\mathrm{Te}$ is $\sim 3.0$ and $\sim 0.2$ at 900 K, respectively.

Lieb and kagome lattices exhibit two-dimensional topological insulator behavior with ${\mathbb{Z}}_2$ topological classification when considering spin-orbit coupling. In this study, we used a general tight-binding Hamiltonian with a morphological control parameter $\theta$ to describe the Lieb ($\theta =\pi /2$), kagome ($\theta =2\pi /3$), and transition lattices ($\pi /2<\theta <2\pi /3$) while considering intrinsic spin-orbit (ISO) coupling. We systematically investigated the effects of shear and uniaxial strains, applied along different crystallographic directions, on the electronic spectrum of these structures. Our findings reveal that these deformations can induce topological phase transitions by modifying the structural lattice angle associated with the interconversibility process between Lieb and kagome, the amplitude of the strain, and the magnitude of the ISO coupling. These transitions are confirmed by the evolution of Berry curvature and by changes in the Chern number when the gap closes. Additionally, by analyzing hypothetical strain scenarios in which the hopping and ISO coupling parameters remain intentionally unchanged, our results demonstrate that the strain-induced phase transitions arise from changes in the hopping and ISO coupling parameters.

We investigate the topological and nonlinear transport properties of uniaxially strained gapped graphene driven by polarized optical fields. We demonstrate that the interplay between optical polarization and lattice strain fundamentally reshapes the Berry curvature distribution, leading to a valley-dependent sign reversal of both the Chern number and the Berry curvature dipole (BCD). Specifically, circularly polarized light drives a valley-selective topological phase transition, which is explicitly manifested by the directional reversal of the nonlinear anomalous Hall current. Moreover, linearly polarized light breaks the residual mirror symmetry of the strained lattice, thereby activating a transverse BCD component that is strictly forbidden in the static limit. Our results uncover a valley-dependent photocontrol mechanism for topological order and Berry curvature distribution, paving the way for designing optovalleytronic devices based on light-matter interaction.

We demonstrate that topological insulators exhibit an intrinsic interfacial instability that amplifies small interface fluctuations, resulting in chaotic behavior during interface growth. This mechanism is different from conventional interfacial instabilities in crystal growth that are driven by external nonuniformities such as surface diffusion and instead arises from intrinsic electronic properties of topological materials. We find that the boundary states of topological insulators have a pronounced impact on the surface stiffness, which quantifies how strongly a surface resists changes in its shape or orientation. While trivial insulators possess positive stiffness that smooths out surface roughness, topological insulators exhibit negative stiffness that amplifies small shape fluctuations. We derive an effective equation of the interface growth with this negative stiffness and demonstrate that the interface dynamics is governed by the Kuramoto-Sivashinsky equation, a prototypical nonlinear equation exhibiting spatiotemporal chaos.

We investigate analytically and numerically the lateral optical binding force in non-Hermitian nanoparticle dimers with gain-assisted active response. In comparison with conventional plasmonic or dielectric nanostructures with passive behavior, the lateral binding force in an active dimer can be dynamically controlled by the external pumping level. Within a linear-response gain model, we show that in close proximity to a critical point the gain-assisted system can exhibit strong enhancement of the lateral binding force, switching between attractive and repulsive regimes, and the emergence of a pronounced transverse driving force. A variety of configurations are analyzed and discussed, including homo-/heterodimers made from multiple material components, different size parameters in geometry, and varying plane-wave illumination. The forces between the dimer structure are calculated using the Lorentz-force approach in the coupled dipole approximation, as well as rigorous numerical simulation using Maxwell stress tensor formalism, combined with the multiple-multipole scattering theory or a finite-element solver. The results provide a theoretical framework for gain-assisted control of optical forces at the nanoscale and clarify the physical scope of the predicted enhancement for future studies of optically bound matter.

Spin-orbit coupling (SOC) is incorporated into the phaseless plane-wave-based auxiliary-field quantum Monte Carlo (pw-AFQMC) method. This integration is implemented using optimized multiple-projector norm-conserving pseudopotentials, which are derived from the fully relativistic (FR) atomic all-electron Dirac-like equation. The inclusion of SOC enables accurate phaseless pw-AFQMC calculations that capture both electronic correlation and SOC effects concurrently, greatly improving the applicability of the method to studying systems containing heavy atoms. We discuss the form of FR pseudopotentials and detail the corresponding formulations of phaseless pw-AFQMC with a two-component Hamiltonian in the spinor basis. The accuracy of our approach is demonstrated by computing the dissociation energy of molecule ${\mathrm{I}}_2$ and the cohesive energy of bulk Pb, highlighting the large influence of SOC in both. Subsequently, we determine the transition pressure of the III-V compound InP from its zinc-blende to rock-salt phase by constructing and analyzing their respective equations of state.

This work systematically investigates the non-Hermitian chiral skin effect (NCSE) for topological edge states in a square-lattice Haldane model with staggered potential. We clarify two physically distinct mechanisms underlying NCSE: (i) boundary on-site gain/loss that introduces a complex momentum, and (ii) boundary nonreciprocal hopping that endows edge states with a complex Fermi velocity, a new mechanism unexplored in previous work. We show that the complex-Fermi-velocity mechanism yields three unique features absent in the gain/loss NCSE: a linear complex energy spectrum, particle-hole symmetry, and energy-dependent spatial separation of edge modes. We further provide a unified comparative framework for both mechanisms and propose a feasible LC circuit scheme to experimentally realize the NCSE via nonreciprocal hopping. Our results establish that the NCSE is a family of effects arising from distinct non-Hermitian perturbations, greatly extending the understanding and controllability of chiral skin phenomena in open topological systems.

We consider phase transitions out of a general topological phase in $2+1$ dimensions. We assume that the transition is triggered by a single Abelian anyon, which becomes light near the transition and whose worldlines proliferate after the transition. (This proliferation is often referred to as “condensation.”) We describe the transition using a continuum field theory obtained by coupling the corresponding topological quantum field theory (TQFT) to a single complex scalar field associated with this anyon. With these assumptions, we find the most general relativistic field theory for such a transition. Even though for a given TQFT and a choice of anyon, there are infinitely many such field theories, the transition theory depends on only a single additional integer parameter. We analyze all these theories, their global symmetries, and their phases. In generic cases, the theory after the transition can be related to the original one via an Abelian hierarchy construction. In special cases, the theory after the transition is gapless, and with a particular deformation, it is related to the original TQFT by gauging an anomaly-free one-form global symmetry. We also explore the enrichment of this setup by a global $\mathrm{U}\left(1\right)$ symmetry. In some cases, enriching the original TQFT is incompatible with the full transition theory. Finally, we demonstrate our construction with many specific examples.

Using bulk gapless topological superconductors in both 1D and 2D as free fermion model examples, we demonstrate the power of subsystem correlation spectrum (the spectrum of correlation matrix), or equivalently the entanglement spectrum for the case of free fermions, in characterizing the topology of the nontrivial ground state. For the systems considered, we show that signatures of the low-energy spectrum, including both the edge modes and the bulk modes, appear in the correlation spectrum, albeit with different behaviors. This work generalizes the 2D Li-Haldane entanglement spectrum characterization of topological edge states to 2D topological systems with gapless bulk.

An anisotropic flat-band fermion system with linear dispersion along one direction and cubic dispersion along the other was proposed in Sheffer et al. [Phys. Rev. X 13, 021012 (2023)]. Here, we study the effects of long-range Coulomb interaction in this fermion system by renormalization group theory and the Dyson–Schwinger gap equation. Renormalization group analysis reveals that the fermion velocity is always restored along the direction that originally exhibits cubic dispersion. Consequently, in the low-energy regime, the system exhibits behavior similar to that of a two-dimensional Dirac fermion system subject to Coulomb interaction. Using the Dyson–Schwinger gap equation method, we find that an excitonic gap is generated if the Coulomb interaction is sufficiently strong, driving the system into a distinct excitonic insulating state with half-quantized anomalous Hall conductivity. Interestingly, we find that the excitonic gap is much more readily generated by Coulomb interaction in the anisotropic flat-band fermion system than in the Dirac fermion system. Based on this finding, we propose a strategy to observe the half-quantized anomalous Hall conductivity. We also investigate the influence of short-range four-fermion interaction on the anisotropic flat-band fermion system. It is shown that the system is driven into the excitonic insulating phase if the strength of four-fermion interaction exceeds a critical value. Observable quantities of this system in the free case, under weak Coulomb interaction, and in the gapped phase driven by strong interactions are also analyzed.

We adapt the fluid description of fractional quantum Hall states, as seen in Monteiro et al. [Phys. Rev. B 109, 174525 (2024)], to model a system of interacting two-component bosons. This system represents the simplest physical realization of an interacting bosonic symmetry-protected topological (SPT) phase, also known as the integer quantum Hall effect of bosons. In particular, we demonstrate how the fluid dynamical boundary conditions of no penetration and no stress at a hard wall naturally give rise to the two counterpropagating boundary modes expected in these SPT phases. Moreover, we identify energy-conserving hydroboundary conditions that can either create a gap in these edge modes or completely isolate the edge states from the bulk, as described in Altland et al. [Phys. Rev. X 14, 011057 (2024)], where they were termed fragile surface states. These fragile surface states are typically absent in $K$-matrix edge theories and require bulk dynamics to manifest. By leveraging insights from hydrodynamical boundary dynamics, we can further elucidate the intricate surface properties of SPTs beyond the usual topological quantum field theory-based approaches.

The ability to compute electron-phonon coupling from first principles, using density functional perturbation theory and interpolation techniques, has enabled predictive calculations of electronic transport coefficients in crystalline materials. However, these methods are still computationally expensive. Here we present two inexpensive methods to obtain thermoelectric transport properties of semiconductors using a small number of electron-phonon matrix elements calculated from first principles. The first method combines models for coupling of electrons with different phonon modes whose parameters are obtained from $\sim 10$ matrix elements per electronic band and phonon mode calculated from first principles. Within this method, we formulate the acoustic deformation potential model for arbitrary crystal symmetries and band extrema locations. The second method uses machine learning to interpolate $\sim 100$ electron-phonon matrix elements per electronic band and phonon mode on dense reciprocal-space grids in the parts of the Brillouin zone relevant for transport. We apply both methods to two-dimensional ${\mathrm{MoS}}_2$ and show very good agreement with the state-of-the-art method. The calculated thermoelectric properties also agree well with experiments. We find that the machine-learning method is more accurate and straightforward to implement compared to the model approach.