Inertial effects in the stochastic motion of the magnetization of nanomagnets in a uniaxial potential biased by an external field are treated via the corresponding Fokker-Planck equation. This equation can be transformed to a simpler partial differential equation by applying an integral transformation and change of variables. The longitudinal magnetization relaxation function, obtained by solving this equation, simultaneously describes various relaxation modes, namely, a slow interwell mode associated with the reorientation of the magnetization vector through potential barriers, a set of almost degenerate intrawell modes arising due to the motion of the magnetization inside potential wells, as well as a fast relaxation mode caused by the inertia (magnetization nutation). These relaxation modes clearly manifest as three separate bands in the spectrum of the longitudinal component of the magnetic susceptibility tensor. The turnover formula of Mel'nikov and Meshkov is shown to provide a good approximation to the longest relaxation time of the magnetization. Moreover, for small values of the bias field the integral relaxation time has Arrhenius behavior (exponential increase with increasing barrier height), which disappears when the bias field exceeds a critical value.

The temperature dependence of the magnetic moment of bcc α-iron was investigated over the range 300–950 K at pressures of approximately 2 and 6 GPa by in situ neutron powder diffraction. The ${}^{54}\mathrm{Fe}$ isotope, whose neutron scattering length is approximately half that of naturally abundant Fe, was employed to enhance the relative contribution of magnetic scattering. Curie temperatures $\left(T_{\mathrm{C}}\right)$ were determined to be 946(30) K, 838(50) K, and 740(40) K at 2.1, 6.0, and 6.7 GPa, respectively, defining a magnetic phase boundary described by $T_{\mathrm{C}}\left(\mathrm{K}\right)=1043-49\left(7\right)P+1.3\left(1.2\right)P^2$. Upon heating at 6.7 GPa, the α–γ structural transition was observed to follow the magnetic transition. This transition sequence indicates that the magnetic phase boundary lies on the low-temperature side of the α–γ phase boundary. Accordingly, the α–γ transition corresponds to a structural transformation from paramagnetic bcc to paramagnetic fcc iron.

We present fine momentum space resolution resonant elastic x-ray scattering measurements of the magnetic structure of the metallic antiferromagnet ${\mathrm{CoNb}}_3{\mathrm{S}}_6$. Using circular dichroism and full linear polarization analysis of the magnetic scattering, we reveal a noncoplanar double-$\mathit{Q}$ $\left(2Q\right)$ order that is comprised of a noncollinear commensurate component and a long-wavelength incommensurate helical component. This $2Q$ magnetic structure exhibits a staggered scalar spin chirality that forms a modulated stripe like pattern with no uniform component. Measurements of the magnetic structure across many samples reveal a complex domain pattern associated with the magnetic ordering and suggest a lowering of the structural symmetry in ${\mathrm{CoNb}}_3{\mathrm{S}}_6$. We present a symmetry analysis demonstrating that the observed $2Q$ magnetic order breaks all necessary symmetries to enable an anomalous Hall effect and further show how this magnetic order can be naturally explained by four-spin exchange interactions in a metallic magnet. The identification of the magnetic order, associated symmetry breaking, and explanation of its origin provides insight into the mechanism of the unconventional magnetotransport phenomena in ${\mathrm{CoNb}}_3{\mathrm{S}}_6$ and thus can help to determine potential routes for realizing novel electronic phenomena in metallic antiferromagnets.

We introduce time-dependent variational principles to study the nonunitary dynamics of open quantum many-body systems, including dynamics described by the full Lindblad master equation, the non-Hermitian dynamics corresponding to the no-click limit of the fully postselected quantum trajectories, and the dynamics described by a hybrid Lindbladian with a control parameter $\alpha$ which interpolates between the full postselection $(\alpha =0)$ and averaging over all quantum trajectories $(\alpha =1)$. As an application we study the nonunitary dynamics of a lossy or driven-dissipative BCS superconductors, evolving in the presence of two-body losses and two-body pumps. We show that the dynamics in the non-Hermitian limit is qualitatively different than the hybrid dissipative dynamics for any $\alpha >0$, leading to sharp modifications in the universal approach to the driven-dissipative steady states. By considering the dissipative dynamics with pair losses, we show that, as the non-Hermitian limit is approached, the density dynamics evolves from a universal power law to exponential decay that converges towards a quasisteady plateau characterized by the freezing of the particle depletion due to pair losses. The reached quasistationary density increases as a function of the dissipation rate highlighting the emergence of a non-Hermitian Zeno effect in the lossy dynamics. For the driven-dissipative case, the non-Hermitian dynamics skips the infinite temperature steady state reached in the presence of finite contribution of the quantum jumps, and the system can get trapped into an effective negative temperature state. We rationalize these findings in terms of the conservation of the length of the pseudospins which, in the non-Hermitian limit, suppresses the effective single-particle losses and pumps acting on the noncondensed particles.

Andreev bound states are coherent electron-hole superpositions that form in a normal metal through repeated Andreev reflection at a superconducting interface. When the length of a superconducting segment is comparable to the coherence length, the bound states on opposite sides of the segment hybridize through quasiparticle tunneling. In a periodic array, these hybridized Andreev bound states form energy bands below the superconducting gap. We develop a theoretical framework for transport in such Andreev crystals. We demonstrate that, at high interface transparency, a constant phase bias between neighboring superconductors renders the bands directional: one band contains only right-moving and the other only left-moving electronic states. This property leads to a directional conductance that enables the device to operate as a flux- and bias-voltage-tunable filter that allows signal transmission in only one direction.

Intercalated compounds offer a versatile platform for high-temperature superconductivity, as exemplified by sodium-intercalated graphite ($\mathrm{Na}{\mathrm{C}}_8$) with a transition temperature ($T_{\mathrm{c}}$) above 28 K. However, the microscopic origins of their structural robustness and superconducting behavior remain elusive. Here we establish a unified framework integrating stacking geometry, intercalated-cation chemistry, bonding topology, and pressure tuning to uncover the mechanisms governing stability and superconductivity. Through extensive first-principles investigations of 36 designed B-N compounds intercalated with $s$-, $p$-, and early $d$-block cations, we propose an electrogeometric stabilization mechanism in which structural robustness arises from the cooperative balance between optimal charge donation filling bonding σ states and geometric compatibility with the interlayer spacing. This balance enhances lattice rigidity and regulates electron-phonon coupling and band dispersion, thereby governing the superconducting behavior. Notably, the $R\text{−}3m$ phase of $\mathrm{Na}{\mathrm{B}}_2{\mathrm{N}}_2$ exhibits a predicted $T_{\mathrm{c}}$ of $\sim 40.6\mathrm{K}$; evolutionary searches further indicate its feasible synthesis. These findings establish fundamental design principles for realizing high-$T_{\mathrm{c}}$ superconductivity in intercalated materials.

An array of quantum dots coupled via superconductivity provides a new platform for creating Kitaev chains with Majorana zero modes, offering a promising avenue toward topological quantum computing. In this work, we theoretically study the quantum capacitance of a minimal Kitaev chain weakly coupled to an external normal lead. We find that, in the open regime, charge stability diagrams of quantum capcaitance can help to identify the sweet spot of a Kitaev chain, consistent with tunnel spectroscopy. Moreover, the quantum capacitance of a single quantum dot coupled to Andreev bound states reveals the interplay between two distinct parity switching mechanisms: coupling to an external normal lead and intrinsic quasiparticle poisoning. Our work provides useful physical insights into the quantum capacitance and parity dynamics in a quantum-dot-based Kitaev chain device.

The superconductor/ferromagnet/superconductor (S/F/S) Josephson junctions (JJs) with an anomalous ground state phase shift ${\phi }_0\ne 0,\pi$ $({\phi }_0\text{−}\mathrm{S}/\mathrm{F}/\mathrm{S} \mathrm{JJs})$ enable the implementation of the zero-field Josephson diode effect with the possibility to control the diode efficiency and polarity. It is just as important that in this case ${\phi }_0$ provides a coupling between the superconducting phase and the magnetization of the interlayer. Such ${\phi }_0\text{−}\mathrm{S}/\mathrm{F}/\mathrm{S} \mathrm{JJs}$ can be used for superconducting memory and logic circuit applications. Here we present the results of theoretical calculation of the current-phase relationship (CPR), exhibiting the Josephson diode effect and ${\phi }_0\ne 0,\pi$, for a JJ through a specific magnetic material. As the interlayer of the JJ we consider an ultrathin film of intermetallic lanthanide $\left(Ln\right)$-based compound ${\mathrm{GdIr}}_2{\mathrm{Si}}_2$. Using the density functional theory (DFT) methods, we study the electronic structure and magnetic properties of the film. Then the effective tight-binding Hamiltonian (TBH), demonstrating high quantitative consistency with the electronic properties obtained from DFT calculations, is constructed. The TBH is used to calculate CPR in the framework of the Bogoliubov–de Gennes approach. The CPRs demonstrate a pronounced ${\phi }_0$ of the order of unity and a pronounced Josephson diode effect with the diode efficiency $\lesssim 0.3$. Moreover, the efficiency can be controlled via rotation of in-plane magnetization in the interlayer. The prospects for utilizing alternative magnetic $Ln$-based materials of the $Ln{T}_2{X}_2$ family ($T$ is a transition metal and $X$ is a $p$ element from groups III–V) for the implementation in ${\phi }_0\text{−}\mathrm{S}/\mathrm{F}/\mathrm{S} \mathrm{JJs}$ are also discussed.

We present a comprehensive first-principles study of twisted bilayer graphene (tBLG) for a wide range of twist angles, with a focus on structural and electronic properties. By employing density functional theory (DFT) with an optimized local basis set, we simulate tBLG, obtaining fully relaxed commensurate structures for twist angles down to 0.987°. For all angles, the lattice relaxation agrees well with continuum elastic models. For angles accessible to plane-wave DFT (vasp), we provide a detailed comparison with our local basis DFT (siesta) calculations, demonstrating excellent agreement in both the atomic and electronic structures. The dependence of the Fermi velocity and band width on the twist angle shows qualitative agreement with results from an ‘‘exact’’ $\mathbf{k}·\mathbf{p}$ continuum model, but reveals a small twist angle offset. Additionally, we provide details of the low-energy wave-function character, band inversion and symmetries. Our results provide an ab initio reference point for the microscopic structure and electronic properties of tBLG, which will serve as the foundation for future studies incorporating many-body effects.

We report the carrier-density dependence of the magnetotransport property in the correlated Dirac semimetal ${\mathrm{CaIrO}}_3$. In the dilute carrier density region ($n_{\mathrm{H}} \sim 2.2\times {10}^{16}{\mathrm{cm}}^{-3}$) at $2\mathrm{K}$, the mobility exceeds $1.0\times {10}^5{\mathrm{cm}}^2/\mathrm{Vs}$ at $2\mathrm{K}$, and the transverse magnetoresistance reaches $2000\%$ at $12\mathrm{T}$. The analysis of quantum oscillations and Hall conductivity shows that the Fermi velocity is nearly independent of the cross-sectional area of the Fermi surface, or equivalently the carrier density, supporting a $k$-linear dispersion of the Dirac node. The field dependence of magnetoresistivity is nearly $B$-linear in the moderate carrier density region ($n_{\mathrm{H}}\ge 4\times {10}^{16}{\mathrm{cm}}^{-3}$), but scales with $B^{\alpha }$ ($\alpha >2$) in the lower carrier density region. The variation of magnetoresistivity is likely affected by the enhanced long-range Coulomb interaction in the quantum limit, where Dirac electrons are subject to the magnetic confinement.

We report the realization and modeling of a triple-antidot molecule hosting three interacting quantum Hall quasiparticles, with tunnel coupling between antidots tunable via the magnetic field. The measured tunneling conductance spectrum reveals the molecular energy levels arising from the interantidot coupling and Coulomb interaction. A tunneling model is established, which shows good qualitative agreement with experimental observations. In this work, we lay the foundation for the realization of complex systems of antidots for quantum Hall quasiparticles with nontrivial quantum statistics.

Anisotropic photonic time crystals (APTCs), enabled by periodic temporal modulation of a uniform anisotropic medium, exhibit asymmetric momentum-band gap structures and offer unique control over light–matter interactions. Here, we introduce and construct temporal Weyl points (TWPs) in APTCs within a synthetic three-dimensional space defined by two phase parameters and the quasifrequency. The temporal response reveals robust Fermi arcs linking TWPs of opposite topological charge. Unlike spatial counterparts, these Fermi arcs emerge only after the first temporal supercell comprising multiple periods of APTCs, reflecting causality. We further show that TWPs enable tunable emission from stationary charges embedded in APTCs, while the associated Fermi arcs robustly suppress radiation at selected directions and frequencies. Our findings establish temporal Weyl physics in photonic time crystals and uncover new opportunities for topological control of light–matter interactions through the time dimension.

We propose a method for calculating exciton spectra and wave functions for model lattice Hamiltonians, based on real-space electron-hole propagators. We verify that our results agree with those of the continuum approximation in the limit of large Wannier excitons, and propose a simple criterion to estimate the exciton size above which the continuum approximation is quantitatively accurate. We then investigate simple one- and two-dimensional multiorbital lattice models and show that small, Frenkel-like excitons, whose size approaches the lattice constant, can display physics that disagrees with the simplest continuum descriptions (a single-valley quadratic expansion around the minimum gap) not just quantitatively, but qualitatively. Specifically, we identify sharp transitions in the character and momentum of the lowest-energy exciton, enabled by the multiorbital nature of the lattice models.

We investigate high-Chern-number quantum anomalous Hall (QAH) phases in sliding bilayer hexagonal lattices. Lateral displacement between layers acts as a symmetry-reduction mechanism that breaks $C_3$ rotational symmetry and shifts band crossings to generic momenta in the Brillouin zone. When time-reversal symmetry is broken by Haldane-type complex next-nearest-neighbor hoppings, these crossings are gapped, yielding insulating phases with Chern numbers up to $\left|C\right|=4$. The large topological charge arises from asymmetric interlayer hybridization mediated by skew hopping channels, which enable multiple inequivalent band inversions within the four-band manifold and redistribute the Berry curvature. Ribbon calculations confirm the corresponding number of chiral edge modes. Our results establish sliding-controlled interlayer hybridization as a symmetry-driven route to nonadditive high-Chern QAH phases in bilayer systems.

From a symmetry perspective, ferroaxial order belongs to the same symmetry as time-reversal-even pseudovectors. Experimentally, ${\mathrm{K}}_2\mathrm{Zr}{\left({\mathrm{PO}}_4\right)}_2$ is known to undergo a displacive-type phase transition from a nonferroaxial to a ferroaxial phase. To identify the key microscopic ingredients driving this transition, we carry out a quantitative analysis combining density-functional theory calculations and symmetry-adapted closest Wannier analysis. As a result, we show that electric toroidal dipole, electric toroidal octupole, and electric hexadecapole, which belong to the same irreducible representation, make dominant contributions to the ferroaxial transition. In particular, we find that spinless electric toroidal octupoles, which originate from spin-independent off-diagonal real hopping between the $p$ orbitals on P and O atoms and between the $d$ orbitals on Zr atoms and $p$ orbitals on O atoms, provide the most significant contributions. Moreover, we explicitly analyze the orbital characters involved in the relevant hybridizations associated with these multipoles. We further show that the relativistic spin-orbit coupling has a negligible influence on the ferroaxial transition. These results demonstrate that spin-independent orbital hybridization between different orbitals on different atoms plays a crucial role in inducing the ferroaxial transition.

Manifolds with nontrivial topology play an essential role in the study of topological phases of matter. In this paper, we study the nontrivial symmetry response of the (2+1)-dimensional $Z_2$ symmetry-protected topological (SPT) phase when the system is put on a nonorientable manifold: the Klein bottle. In particular, we find that when a symmetry defect is inserted along the orientation-reversing cycle of the Klein bottle, the ground state of the system gets an extra charge. This response remains well defined at transition points into the trivial SPT phase, resulting in an exact twofold degeneracy in the ground state independent of the system size. We demonstrate the symmetry response using exactly solvable lattice models of the SPT phase, as well as numerical work across the transition. We explore the connection of this result to the modular transformation of the (3+1)-dimensional $Z_2$ gauge theory and the emergent nature of the parity symmetry in the $Z_2$ SPT phase.

Thermoelectric (TE) materials enable sustainable bidirectional conversion between heat and electricity, facilitating waste heat recovery and cooling. However, optimizing their performance is challenging due to the intertwined and often competing nature of electronic and thermal transport properties. Although high-throughput screening accelerates discovery, computational costs often limit simultaneous accuracy in both electronic and thermal predictions. Here, we develop a first-principles framework that incorporates key scattering mechanisms for both electrons and phonons and solves the Boltzmann transport equation to compute electronic and lattice thermal transport properties. This approach enables efficient and accurate evaluation of 1136 semiconductors, compiled into an interactive database. Herein, we identify promising TE candidates with band gaps between 0 and 0.8 eV, allowing effective Fermi level tuning. Experimental synthesis of one candidate ScPtSb confirms excellent TE performance, validating our predictive approach. In this work, we provide a robust computational resource and guidance for accelerated development of high-performance TE materials.

We compute and analyze the dependence of excitonic second- and third-harmonic generation (SHG/THG) as a function of the optical excitation intensity in the presence of static electric fields by solving the semiconductor Bloch equations. Our simulations are performed for excitation of the strongly bound intralayer exciton of an inversion-symmetric homobilayer of ${\mathrm{MoS}}_2$ with in-plane electric fields. We demonstrate that for resonant excitation at the $1s$ K-exciton the SHG and the THG show complex dependencies on both the strength of the static field and the peak amplitude of the optical pulse. For sufficiently intense optical excitation, the THG increases and the SHG increases superlinearly with the amplitude of the static field as long as exciton ionization is not yet dominating. Microscopic simulations demonstrate that these dependencies arise from an interplay between several effects including static and transient Stark shifts, exciton ionization, off-resonant Rabi oscillations, and a modified interference between optical nonlinearities induced by the intraband acceleration. Our findings offer several new possibilities for controlling the strong-field dynamics of systems with strongly bound excitons.