One-electron self-interaction errors (SIE), caused by incomplete cancellation of the electron's spurious self-Coulomb interaction, pose a persistent challenge in density functional approximations, as illustrated by the prototypical one-electron system ${\mathrm{H}}_2^{+}$. While significant efforts have been made to eliminate SIE through the development of computationally expensive nonlocal density functionals, it is equally important to explore whether SIE can be mitigated within the framework of more efficient semilocal density functionals. In this Letter, we present a nonempirical exchange-only meta-generalized gradient approximation (meta-GGA) that incorporates the Laplacian of the electron density. Our results demonstrate that this meta-GGA significantly reduces SIE, yielding a binding energy curve for ${\mathrm{H}}_2^{+}$ that matches the exact solution at equilibrium and improves across a broad range of bond lengths over those of the Perdew-Burke-Ernzerhof and strongly constrained and appropriately normed semilocal density functionals. This advancement paves the way for further development within the realm of semilocal approximations.

Equilibration plays a fundamental role in our understanding of statistical mechanics and the long-time dynamics of many-body systems. In quantum systems, the route to equilibration is intimately related to level repulsion and quantum signatures of chaos that are encoded in their unitary evolution. Chaotic quantum systems exhibit level statistics characteristic of ensembles of random matrices. In this work, we demonstrate that single-particle chaos leads to equilibration of many noninteracting photons. We show that the underlying mechanisms for equilibration are operator spreading and quantum interference. More specifically, we demonstrate that the unitary dynamics of a general Floquet system implemented using single-mode phase shifters and multiport beamsplitters leads to equilibration of photons. We propose a realistic photonic implementation of the multiparticle kicked rotor, which is a Floquet system that we use as a concrete example of our general approach.

The discovery of unconventional antiferromagnets, such as altermagnets, has drawn significant attention to higher-rank magnetic multipoles, particularly magnetic octupoles. Despite the advances in research, attempts to understand their microscopic properties remain limited due to the unbounded nature of the position operator in bulk crystals. In this paper, we address this problem by using a well-known thermodynamic approach and derive a formula for the spin magnetic octupole moment (SMOM) that can be used in bulk crystals. The resulting formula is gauge invariant and satisfies Středa formulas that relate the SMOM to the spin magnetoelectric dipole-quadrupole susceptibilities. Furthermore, we apply this formula to several models and examine the fundamental properties of the SMOM. For example, in $d$-wave altermagnets, the nonrelativistic component of the SMOM, which is independent of spin-orbit coupling, is larger than the relativistic component, which is induced by spin-orbit coupling. These nonrelativistic SMOMs have the same microscopic origin as nonrelativistic spin splitting that characterizes $d$-wave altermagnetism. Moreover, they exhibit a Néel vector dependence consistent with Landau theory for $d$-wave altermagnetism [Phys. Rev. Lett. 132, 176702 (2024)].

We study the nature of the debated thermal Hall effect in the candidate Kitaev material $\alpha \text{−}{\mathrm{RuCl}}_3$. Without assuming the existence of a gapped spin liquid, we show that a realistic minimal spin model in the canted zigzag phase suffices, at the level of linear spin-wave theory, to qualitatively explain the observed temperature and magnetic field dependence of the nonquantized thermal Hall conductivity ${\kappa }_{xy}$, with its origin lying in the Berry curvature of the magnon bands. The magnitude of the effect is, however, too small compared to the measurement by Czajka et al. [Nat. Mater. 22, 36 (2023)]—after scanning a broad range of model parameters ($6\times {10}^5$ different sets), we find an empirical upper bound on ${\kappa }_{xy}/T$ to be $\sim 0.2\pi k_B^2/6\hslash$ or about $40\%$ of the value expected from Majorana edge modes. Recent experiments suggest that phonon contribution to the thermal Hall effect cannot be neglected. We show that even by including magnetoelastic coupling of phonons to spins, the resulting intrinsic contribution, from both magnons and phonons, is, however, still insufficient to explain the observed magnitude of the Hall signal. After careful analysis of the extrinsic phonon mechanisms, we use the recent experimental data on thermal transport in $\alpha \text{−}{\mathrm{RuCl}}_3$ by Lefrançois et al. [Phys. Rev. X 12, 021025 (2022)] to determine the phenomenological ratio of the extrinsic and intrinsic contributions, $\eta \equiv {\kappa }_{xy}^E/{\kappa }_{xy}^I$. We find $\eta =1.2\pm 0.5$, i.e., the extrinsic contribution, most likely due to side-jump scattering of phonons off of defects, contributes about half of the observed thermal Hall. When combined with our computed intrinsic value, this quantitatively explains both the magnitude and detailed temperature dependence of the experimental thermal Hall effect in $\alpha \text{−}{\mathrm{RuCl}}_3$.

Stable three-dimensional topological skyrmion structures in frustrated magnets are investigated. The texture exhibits a helicoid pattern along the vertical direction, described by a position-dependent helicity, which interpolates between Neel- and hedgehoglike two-dimensional skyrmions, characterized by the Hopf index, and is referred to as “twisted skyrmion tubes” (TSkTs). The stability and topology of TSkTs are achieved by competing next-nearest-neighbor exchange interactions, the thickness of the magnet, and the applied magnetic field. The dynamical behavior of a twisted structure in frustrated magnets is determined. Specifically, we derive that the helicity dynamics of the TSkT can be driven by an electric current resulting from spin-orbit torque interaction. Furthermore, we address the study of the electronic scattering problem using a spin-orbit-torque-driven TSKT, which offers promising applications for low-power storage nanodevices and nanobatteries with enhanced control.

The non-Hermitian skin effect (NHSE) has emerged as a hallmark of non-Hermitian physics, with far-reaching implications for transport, topology, and sensing. While recent works have uncovered the NHSE in magnetic systems, these analyses rely on effective non-Hermitian Hamiltonians, thereby leaving open critical questions regarding their applicability and predictive power in experimentally feasible platforms. Here, we address this gap by exploring both the non-Hermitian and Liouvillian dynamics of a spin chain coupled to a shared bosonic reservoir. We identify the parameter regime in which these frameworks yield congruent predictions, while showing that the non-Hermitian approach fails to capture essential dynamical features—such as relevant timescales and conditions for experimental observability. Our analysis also reveals that the NHSE stems from the interplay between chiral spin couplings and reciprocal nonlocal dissipation—two interactions that can naturally occur in magnetic crystals and be easily engineered in magnetic heterostructures. Focusing on a concrete example of such heterostructures, we establish an explicit connection between their Landau-Lifshitz-Gilbert dynamics and our microscopic model, providing a tangible route toward realizing the NHSE in an experimentally relevant spintronics setup.

The structures of the superconducting spin valve (SSV) ${\mathrm{Fe}/\mathrm{Si}}_3{\mathrm{N}}_4/\mathrm{Pb}/{\mathrm{Si}}_3{\mathrm{N}}_4/\mathrm{Fe}$ (where ${\mathrm{Si}}_3{\mathrm{N}}_4$ is a dielectric insulating layer of controlled thickness) were investigated. The dependence of the magnitude of the SSV effect on the thicknesses of the superconducting (S) and insulating (I) layers was studied. Optimization of the S and I layer thicknesses enabled a complete switching between the normal and superconducting states when the mutual orientation of the magnetizations of the ferromagnetic (F) layers changed from antiparallel to parallel. A maximal SSV effect value of 0.36 K was achieved in an external magnetic field of 1 kOe. These results demonstrate that SSV structures with tunable S/F interface transparency controlled by insulating interlayers are promising for achieving a significant magnitude of the effect. This opens new avenues for the development of such systems and their potential applications in spintronic devices.

We systematically investigate the topological properties of a one-dimensional non-Hermitian Kitaev chain with long-range coupling, where three different cases, with nonreciprocal superconducting pairing terms, nonreciprocal couplings, and complex on-site energies, are considered. It is found that topological nonzero modes exist in three cases and the topological phase transition cannot be induced by the nonreciprocal superconducting pairing terms and imaginary on-site potential. However, the system undergoes a topological phase transition when appropriate nonreciprocal hoppings are introduced. Although the introduction of the long-range interaction can suppress the non-Hermitian skin effect, it can remerge under specific parameters when three non-Hermitian factors are considered simultaneously. Our findings provide a thorough understanding of the effect of non-Hermitian parameters in the topology of the non-Hermitian Kitaev chain with the long-range couplings, and extend the understanding of the long-range couplings in non-Hermitian physics.

We use tools based on the modern theory of polarization for a numerical study of the localization transition of the Aubry-André model. In this model, the spatial modulation of the potential, $\alpha$, is an irrational number, which we approximate as the ratio of Fibonacci numbers, $F_{n+1}/F_n$, where $F_n=L$ is also the system size. We determine the phase diagram as a function of particle density (filling) and potential strength $W$. We calculate the geometric Binder cumulant and also apply a renormalization approach. In accordance with an earlier study, we find that at certain fillings the transition occurs at $W=0$, while at others it occurs at $W=2t$ ($t$ is the hopping parameter). Using the Zeckendorf decomposition of natural numbers, we show that the $W=0$ fillings tend to irrational fillings given by the infinite limit of ratios of Fibonacci numbers. When a given filling is a “good” approximation to the irrational number to which it tends in the thermodynamic limit, the transition tends to $W=0$; if this is not the case, then $W=2t$. We also observe that “quasiperiodic” energy bands form, i.e., states cluster, and there are gaps between the clusters. We conjecture that the formation of these quasiperiodic bands is also related to how well a given filling approximates its irrational infinite limit. We also study an extension of the original Aubry-André model with second-nearest-neighbor hoppings. This model also exhibits a distorted phase diagram compared to the original one, with spikes that do not necessarily tend to zero, but to finite values of $W$, determined by the modified band structure.

Compounds of Sn, such as SnSe and SnS, exhibit novel phonon characteristics and low thermal conductivity, making them emerging star materials in the thermoelectric family. In this work, through the Boltzmann transport equation scheme and the Wigner thermal transport model, quasi-one-dimensional mixed-valent $\mathrm{S}{\mathrm{n}}_2{\mathrm{S}}_3$ were found to exhibit a low thermal conductivity along the $c$ axis with a weak temperature dependence. The low thermal conductivity is attributed to the anharmonic rattling vibrations of weakly bonded Sn(II) atoms, which are influenced by the Coulomb interaction of lone pairs at adjacent Sn(II) atoms. The rattling of Sn(II) induces low-frequency flat optical phonons and avoids crossing behavior. The atomic displacements and mean square displacement analysis reveal that Sn(II) atoms exhibit significantly greater and anisotropic displacements compared to Sn(IV) and S, confirming that Sn(II) behaves as a rattler. The results obtained from this work suggest an opportunity to discover low thermal conductivity in mixed-valent compounds.

Superconductor-semiconductor hybrids have been shown to be useful for realizing the Josephson diode effect, where nonreciprocity in the supercurrents occurs due to the interplay of the Josephson effect and applied magnetic fields. With the same ingredients, these Josephson junctions can also host Andreev and Majorana bound states, whose interplay with the Josephson diode effect is, however, not fully understood. In this work, we consider short Josephson junctions based on superconductor-semiconductor systems under homogeneous Zeeman fields and investigate the Josephson diode effect in the presence of Andreev and Majorana states. Under generic conditions, the Zeeman field component parallel to the spin-orbit axis promotes an asymmetric low-energy spectrum as a function of the superconducting phase, which persists in the trivial and topological phases hosting Andreev and Majorana bound states, respectively. Interestingly, this spectrum asymmetry originates supercurrents that are not odd functions of the superconducting phase difference as in common Josephson junctions, thereby developing a nonreciprocal behavior that signals the emergence of the Josephson diode effect. We show that the Josephson diode effect is particularly promoted under the presence of both zero-energy Andreev and Majorana bound states, revealing that Josephson diodes can be realized in the trivial and topological phases of superconductor-semiconductor hybrids. We then demonstrate that the Zeeman field evolution of the diode's efficiencies is able to map the topological phase transition and the formation of Majorana bound states via an oscillatory behavior that becomes more visible in long superconductors. While Josephson diodes generally exist in the trivial and topological phases of Josephson junctions, we discover that in the tunneling regime only a Josephson diode effect in the topological phase remains due to the finite contribution of Majorana bound states. Our findings help understand the Josephson diode effect in superconductor-semiconductor hybrids and can also be useful for guiding the realization of Majorana-only Josephson diodes as well as for identifying Majorana states.

The magnetic kagome materials are a promising platform to study the interplay between magnetism, topology, and correlated electronic phenomena. Among these materials, the $R{\mathrm{Ti}}_3{\mathrm{Bi}}_4$ family received a great deal of attention recently because of its chemical versatility and wide range of magnetic properties. Here, we use angle-resolved photoemission spectroscopy measurements and density functional theory calculations to investigate the electronic structure of ${\mathrm{TbTi}}_3{\mathrm{Bi}}_4$ in paramagnetic and antiferromagnetic phases. Our experimental results show the presence of unidirectional band splitting of unknown nature in both phases. In addition, we observed a complex reconstruction of the band structure in the antiferromagnetic phase. Some aspects of this reconstruction are consistent with effects of additional periodicity introduced by the magnetic ordering vector, while the nature of several other features remains unknown.

To evaluate the effectiveness of machine learning in systems with competing interactions, we developed a self-learning quantum Monte Carlo (SLQMC) method to simulate the phase transition in the classical Holstein spin-fermion model. In SLQMC, machine-learning techniques are employed to approximate the free energy, thereby bypassing the need for exact diagonalization and significantly reducing computational cost. We assess the performance of SLQMC using both linear regression and neural network models. Our results show that both models are capable of capturing the phase transition from the antiferromagnetic (AFM) state to the charge-density-wave (CDW) state. However, the sampling efficiency decreases near the AFM-CDW phase transition, which is attributed to the increased mean-squared error of the machine-learning model. Additionally, the sampling efficiency decreases with increasing lattice size. This suppression is due to the increased root-mean-squared error as the machine-learning model is applied to a large lattice and the finite-size effect, wherein the energy gap between the ground state and low-energy excited states decreases as the lattice grows. Our findings highlight the necessity of highly accurate machine-learning models to simulate theoretical models with complex, competing microscopic interactions on a large lattice.

The high thermal conductivity and ambipolar mobility of cubic boron arsenide (BAs) make it a promising material for electronic devices that require efficient heat dissipation. For practical applications of BAs, searching for optimal dopants to realize controlled doping is a central issue. This work systematically explores substitution impurities ${\mathrm{C}}_{\mathrm{As}}$, ${\mathrm{Si}}_{\mathrm{As}}$, ${\mathrm{Ge}}_{\mathrm{As}}$, and ${\mathrm{Be}}_{\mathrm{B}}$ that can act as acceptors in BAs. The formation energy and optimal growth condition for each impurity are determined. Converged ionization energies of the impurities are obtained by the potential patching method with large supercells containing over ${10}^4$ atoms. The thermal conductivity of doped BAs is evaluated by combining a machine-learning force field and the Green-Kubo method. ${\mathrm{Be}}_{\mathrm{B}}$ is identified as a superior dopant for heavy $p$-type doping in BAs. Due to its low formation and ionization energies, ${\mathrm{Be}}_{\mathrm{B}}$ has a good solubility in BAs and is able to introduce $\sim {10}^{20}{\mathrm{cm}}^{-3}$ hole density. Meanwhile, in the ${\mathrm{Be}}_{\mathrm{B}}$ heavy doping region, BAs maintains a high thermal conductivity. These good properties stem from the small mismatch in atomic size and mass between Be and B. The findings can be helpful for the doping control of BAs.

As a universally employed strategy for suppressing phonon propagation, element doping plays a critical role in reducing lattice thermal conductivity ${\kappa }_L$ of thermoelectric materials. Traditionally, heavy-element doping with a substantial atomic mass/radius difference leads to a pronounced ${\kappa }_L$ reduction through the phonon velocity attenuation and phonon scattering enhancement. In this study, using accurate neural network potentials combined with the phonon Boltzmann transport equation, we systematically investigate the comparative impacts of isoelectronic (Ge, Pb) and aliovalent (Ag) doping on phonon transport in SnSe. Counterintuitively, despite the fact that Pb has a heavier atomic mass and exhibits a greater mismatch in both mass and radius compared to Sn, aliovalent Ag doping achieves superior ${\kappa }_L$ suppression than isoelectronic Pb doping. While the softening of acoustic and optical phonons, resulting, respectively, from weakened bond strength and enhanced electron screening, contributes to some reduction in phonon group velocity of Ag-doped SnSe, it is not the main mechanism. The anomalous suppression of ${\kappa }_L$ is primarily attributed to the enhanced coupling between the acoustic and optical phonon branches. Further results reveal that the p-d antibonding interaction between $\mathrm{Se}\text{−}4p$ and $\mathrm{Ag}\text{−}4d$ orbitals induces the weakening of bond strength, thereby causing the downward shift of low-frequency optical branches and thus enhancing the coupling effect between acoustic and optical branches. This work deepens our understanding of the phonon transport mechanism in aliovalent-doped materials and provides theoretical guidance for experimentally reducing the ${\kappa }_L$ through doping strategies.

Interlayer stacking in two-dimensional van der Waals heterostructures offers a powerful means to tune crystal symmetry and charge distribution. In this work, we designed a low-mismatch heterostructure consisting of arsenene and ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ (CIPS), in which interface-induced effects stabilize a high-polarization (HP) phase. First-principles calculations demonstrate that orbital symmetry matching between Cu and As atoms promotes the spontaneous formation of Cu-As bonds, which enhances Cu displacement and interlayer charge redistribution, thereby strengthening the out-of-plane polarization. Building on this mechanism, we proposed a trilayer chiral moiré superlattice of arsenene/CIPS/arsenene as a ferroelectric memory array, featuring two discrete polarization domains with a maximum polarization of 7.00 pC/m and an estimated storage density of ${10}^{10}\mathrm{bits}/{\mathrm{mm}}^2$. Arsenene coupling, particularly via Cu-As bonds, further increases the ferroelectric switching barrier and Curie temperature. These findings present a pressure-free strategy for stabilizing the HP phase of CIPS at room temperature and provide a promising platform for high-speed, high-density, nonvolatile ferroelectric memory applications.

Electrides are materials in which some of the electrons are localized at the interstitial sites rather than around the atoms or along atomic bonds. Most elemental electrides are either alkali metals or alkaline-earth metals because of their low ionization potential. In this work, we report that elemental silicon becomes an electride at pressures exceeding 400 GPa. With ab initio molecular dynamics (MD) simulations, we study this behavior for silicon, sodium, potassium, and magnesium at high pressure and temperature. We performed simulations for liquids and ten crystal structures. Charge density and electron localization functions (ELF) are analyzed for representative configurations extracted from the MD trajectories. By analyzing a variety of electride structures, we suggest the following quantitative thresholds for the ELF and charge density in each interstitial site to classify high-pressure electrides: (1) the maximum ELF value should be greater than 0.7, (2) there should be at least 0.9 electrons near the ELF basin, and (3) the Laplacian charge density, ${\nabla }^2\rho \left({\mathbf{r}}_0\right)$, should be negative with magnitude greater than ${10}^{-3}e/{\mathrm{bohr}}^5$. Finally, we compute x-ray diffraction patterns to determine the degree to which they are affected by the electride formation. Overall, this framework could become a benchmark for future theoretical and experimental studies on electrides.

We investigate the fractal energy spectrum and quantum Hall response of a two-dimensional 1/5-depleted square lattice subjected to a perpendicular magnetic field. Using a tight-binding model that includes both nearest-neighbor $\left(t_1\right)$ and next-nearest-neighbor $\left(t_2\right)$ hopping, we compute the Hofstadter butterfly and extract quantized Hall conductivities via Chern number calculations. In the absence of diagonal hopping $(t_2=0)$, the spectrum exhibits exact particle-hole and flux-inversion symmetries, and the total Chern number across all bands vanishes. When $t_2$ is introduced, these symmetries are broken, the butterfly becomes deformed, new gaps open, and remarkably a nonzero total Chern sum can emerge, signaling unconventional topological phases. By systematically varying $t_1$ and $t_2$, we identify regimes with large individual Chern indices and parameter windows where gap stability and Hall plateaus are optimized. Our results demonstrate that lattice depletion combined with diagonal hopping provides a tunable route to engineer robust Chern insulators in both artificial and oxide-based square-lattice systems.

Carbon-framework-based nanostructures (CFBNs) with atomically precise well-tailored carbon-vacancy defect structures hold significant potentials for application in optoelectronic devices and catalysis materials. However, a major challenge for the practical application of these materials is their notable low conductivity. In this study, we conducted terahertz time-domain spectroscopy (THz-TDS) measurements and first-principles calculations to investigate the transport properties of CFBNs with different carbon-vacancy defect structures or porous configurations. Our THz-TDS measurements reveal that high carrier densities exist in CFBNs we studied and show that electron scattering at disordered lattices domains and defect or porous edges significantly reduces carrier mobility. Despite the observed high carrier densities, our first-principles calculations revealed a semiconducting band structure for pristine CFBNs and deep transition energy level for native defects. By combining these calculated results with the measured conductivity and carrier density, we propose that the high carrier density observed in CFBN samples is the result of thermally excited charge carriers in localized states, while the low conductivity is contributed by carrier hopping in localized states and extreme scattering in extended states. Both of these phenomena are induced by the disordered lattices in CFBNs. Our findings provide insights into the transport properties of CFBNs, which are essential for the advancement of high-performance carbon-based devices.