This study numerically investigates magnetization reversal processes driven by an external magnetic field in three-dimensional antiferromagnetic spin models with weak random-field disorder. Considering an extremely weak disorder and low temperature, we observe a stepwise hysteresis loop and the appearance of short magnetization bursts of a characteristic triangular shape; the number of bursts increases with disorder, indicative of Barkhausen-type noise. These phenomena are attributed to the simultaneous reversal at a given external field of segments composed of spins with identical neighborhoods. A local random field orients one or more spin neighbors, resulting in small, ferromagneticlike clusters distributed throughout the system. As disorder increases, these clusters may merge to form a labyrinthine structure within the antiferromagnetic background, facilitating brief avalanche propagation. The results demonstrate that, compared with familiar random-field ferromagnets, the observed antiferromagnetic Barkhausen noise and the related avalanche sequence have a profoundly different structure, organized into peaks associated with the transition between magnetization plateaus. They exhibit prominent cyclical trends and disorder-dependent multifractal fluctuations, with the singularity spectrum quantifying the degree of disorder. The activity avalanches exhibit scale invariance resembling that recently found in experiments with disordered $\text{ferr}i\text{magnets}$ and martensites, as well as in quantum Barkhausen noise, which are associated with active geometric regions rather than individual-spin dynamics. The observed scaling behavior is interpreted in terms of self-organized critical dynamics.

We present a single-shot near-field technique, where the near-field scan is performed on a single sample without repeating measurements or averaging over multiple samples, to reconstruct the isofrequency surfaces of metamaterials in the microwave regime. In our approach, we excite resonant modes using a fixed source in a resonator composed of the material under test and map the in-plane field distribution with a movable probe. Applying a fast Fourier transform to the measured field reveals the sample's in-plane dispersion. By extending this analysis over multiple frequencies and comparing the results with Fabry-Pérot resonances, we retrieve the full three-dimensional dispersion relation. When we apply the method to a double nonconnected wire metamaterial, it accurately captures the low-frequency hyperbolic isofrequency surface, providing both a precise experimental tool and conceptual insight into spatially dispersive metamaterials.

We develop a Fokker-Planck approach to describe the dynamics of staggered magnetization and thermal fluctuations in a two-dimensional antiferromagnetic system with uniaxial anisotropy. Beginning with a classical model for the antiferromagnetic system, we incorporate a Landau-Lifshitz-Gilbert equation augmented by Langevin fields to account for thermal fluctuations, and we derive the Fokker-Planck equation governing the probability distribution function of the spin configuration. Employing the mean-field approximation, we derive the equations of motion for the spin polarization and the two-time spin-spin correlation functions. The methodology is applied to the study of spin-wave dynamics and to the formulation of a phenomenological model for resistance fluctuations in two-dimensional antiferromagnetic semiconductors.

In the framework of tight-binding models and the Green's function method, the mechanical modulation of the chirality-induced spin selectivity (CISS) in chiral molecular junctions is investigated. The results demonstrate that the CISS is weakened monotonically by stretching the molecule, while the change is nonmonotonic in the case of compression. A moderate compression enhances the CISS effect, while a strong compression induces destructive quantum interference (DQI) in the transmission, which generates large spin polarization around the DQI features associated with discrete and irregular spin polarization peaks. We explain the DQI mechanism in terms of interference of multiple paths in a simplified model for the chiral molecule. The variations of long-range electron hopping and spin-orbit coupling under molecular deformation are found to be crucial. For very strong compression, the DQI and the CISS are suppressed. This work proposes a feasible way to modulate the CISS in chiral molecular junctions by deepening our understanding of CISS in the presence of deformation.

${\mathrm{LaNiGa}}_2$, as a time-reversal symmetry breaking superconductor, has garnered significant attention due to distinctive Dirac points and nonunitary triplet pairing. Here, we investigate the superconducting properties of ${\mathrm{LaNiGa}}_2$ under high pressure and uncover a dome-like behavior in its superconducting phase, with a maximum critical temperature $T_{\mathrm{C}}$ of 3.2 K at approximately 16 GPa. Remarkably, superconductivity abruptly vanishes above 26 GPa, coinciding with an orthorhombic-to-monoclinic structural transition. This pressure-driven evolution may be closely linked to distinct energy shifts of Dirac points and electron-phonon coupling enhancement. Our findings reveal a profound interplay between topological electronic band structure and time-reversal symmetry breaking superconductivity in ${\mathrm{LaNiGa}}_2$, offering new insights into the engineering of quantum materials through symmetry and band structure control.

Inspired by recent developments in electron chirality, we reconsider some microscopic physical quantities that have been overlooked or have received little attention in condensed-matter physics, based on the nonrelativistic limit of the Dirac bilinears in relativistic quantum theory. We identify the expression of physical quantities defined by the four-component Dirac field in terms of the two-component Schrödinger field, which is usually used in condensed-matter physics, and clarify its conjugate electromagnetic field. This consideration bridges the fields of condensed-matter physics, quantum chemistry, and particle physics, and paves the way to electromagnetic control of matter. Our findings provide a means of ab initio quantification of material characters such as chirality and axiality that are unique to low-symmetry materials, and stimulate the systematic search for useful, new functionalities.

We determine the finite-temperature phase diagram and critical behavior of the classical square-lattice Heisenberg-compass model using large-scale Monte Carlo simulations and finite-size scaling. Six symmetry-distinct ordered phases are identified. The four phases that simultaneously break the spin-lattice $C_4$ and in-plane spin-inversion symmetries undergo continuous transitions in the Ashkin-Teller universality class, with the associated critical lines terminating at four-state Potts points, beyond which the transitions become first order. In contrast, the two $z$-polarized phases display conventional two-dimensional Ising criticality. Our results reveal how the interplay between Heisenberg exchange and compass anisotropy organizes these distinct critical regimes, thereby completing the characterization of the model's thermal phase transitions.

We study charge and spin transport in systems composed of itinerant electrons and localized magnetic moments of a Kitaev quantum spin liquid (QSL) phase. For example, $\alpha \text{−}{\mathrm{RuCl}}_3$ either is intrinsically doped or in proximity to graphene. Our analysis reveals distinct temperature-dependent transport behaviors due to the QSL gap and the Majorana excitation spectrum, which are greatly enhanced when the velocities of itinerant electrons and QSL excitations become comparable. These transport characteristics could potentially be employed to reveal the fractionalized excitations of the spin liquid. Furthermore, the observed proportionality between spin and charge relaxation rates identifies a novel realization of Elliott-Yafet relaxation mediated by the fractionalized excitations of a quantum spin liquid.

We present two quantum-classical hybrid methods for simulating the time-dependence of electron-phonon systems that treat electronic correlations numerically exactly and optical-phonon degrees of freedom classically. These are a time-dependent Lanczos and a matrix-product state method, each combined with the multitrajectory Ehrenfest approach. Due to the approximations, reliable results are expected for the adiabatic regime of small phonon frequencies. We discuss the convergence properties of both methods for a system of interacting spinless fermions in one dimension and provide a benchmark for the Holstein chain. As a first application, we study the decay of charge-density wave order in a system of interacting spinless fermions coupled to Einstein oscillators and in the presence of quenched disorder. We investigate the dependence of the relaxation dynamics on the electron-phonon coupling strength and provide numerical evidence that the coupling of strongly disordered systems to classical oscillators leads to delocalization, thus destabilizing the (finite-size) many-body localization in this system.

Atomically thin metallenes have emerged as a new member of the two-dimensional (2D) materials family. Recent experimental realization of metallenes in the Ångström limit has further intensified interest in this class of 2D materials. However, achieving subatomic insight into them demands the most detailed and systematic characterization of their electronic structure. Such understanding is essential for the rational design and exploitation of their properties in plasmonics, catalysis, and quantum optics. Existing electronic-structure studies are either scattered or focus on a few selected systems, and a comprehensive view of their band structures and Fermi surfaces remains missing. Here, we address this gap by studying 45 elemental metallenes in six monolayer lattices (honeycomb, square, hexagonal, and their buckled forms) using density-functional theory. We found that lattice type primarily fixes the shape and radial placement of the Fermi lines, while out-of-plane buckling introduces controlled modifications: it shortens long straight Fermi-line segments, and occasionally creates, removes, or merges small Fermi-line pockets. The electronic configuration determines which orbital type dominates the Fermi level. We summarized Fermiology using a single score for each element, termed pocketness, derived from four descriptors that combine element properties (symmetry, coordination) with electronic characteristics (dispersion, Fermi-surface topology). This score enables targeted angle-resolved photoemission spectroscopy (ARPES) tests, controlled Lifshitz transitions, and provides a predictive basis for transport and device applications.

A quantum spin liquid hosts massive quantum entanglement whose identification is one of the most significant problems in physics. Yet, its detection is known to be notoriously difficult because of featureless properties without a symmetry order parameter. Here, we demonstrate dynamic signatures of a quantum spin liquid state by investigating Kitaev's spin model on the hyperhoneycomb lattice, where a quantum spin liquid state is stabilized as a stable thermodynamic phase. The real-time dynamics of spin correlation function is obtained with the large-scale quantum Monte Carlo simulation. We find the onset of a characteristic oscillation in dynamic local spin correlation as entering the quantum spin liquid phase. Our results show that an isotrophic three-dimensional Kitaev spin liquid can be characterized by a sharp growth of coherent spin dynamics of the system, which we refer to as a dynamic order. We further propose that a dynamic order may help detect a class of featureless symmetric thermal transitions.

The nuclear quantum effects (NQEs) induce pronounced displacements of light nuclei (e.g., hydrogen and positive muons) from their equilibrium positions, profoundly altering material properties. Conventional treatments of zero-point motion often fail to accurately predict experimental observables, particularly for ultralight particles like the positive muon. In this work, we employ a combination of ab initio methods to explicitly simulate the nuclear spatial distributions in muoniated benzene (${\mathrm{C}}_6{\mathrm{H}}_6\mathrm{Mu}$). Our simulations reveal pronounced anharmonic effect and strong temperature dependence in nuclear distributions. Moreover, the hyperfine couplings for muons and protons obtained from path integral molecular dynamics (PIMD) simulations show quantitative agreement with muon spin resonance ($\mu \mathrm{SR}$) experiments. These results demonstrate that PIMD offers a reliable framework for capturing NQEs and provides unique insights into the behavior of light nuclei in $\mu \mathrm{SR}$ spectroscopy.

The development of predictive theories for spin and valley properties in $\mathrm{W}{\mathrm{S}}_2/{\mathrm{CrBr}}_3$ heterostructures requires fundamental understanding of nonmagnetic vacancy effects. Using density functional theory calculations, we find that nonmagnetic vacancies significantly enhance the spin-orbit splitting at the $K$ and $K$′ valleys in the conduction band minimum of monolayer $\mathrm{W}{\mathrm{S}}_2$ (78.2 meV for W vacancies). However, valley splitting remains prohibited due to preserved time-reversal symmetry. By constructing a van der Waals heterostructure with a monolayer ${\mathrm{CrBr}}_3$ magnetic substrate induces weak exchange interactions, generating a minor valley splitting (−0.8 meV). Remarkably, vacancy engineering amplifies this effect: sulfur vacancies (${\mathrm{V}}_1-{\mathrm{V}}_4$) induce valley splitting ranging from 3.2 to 9.0 meV, while specific tungsten vacancies (${\mathrm{V}}_6$) achieve a maximum valley splitting of 13.2 meV. Our findings reveal that vacancy-induced orbital hybridization and asymmetric potential gradients enhance Rashba spin-orbit coupling. Furthermore, the combining between nonmagnetic vacancy symmetry in $\mathrm{W}{\mathrm{S}}_2$ and weak magnetic exchange from ${\mathrm{CrBr}}_3$ establishes an unconventional symmetry protection mechanism for valley splitting enhancement. This defect engineering strategy provides a pathway for designing tunable valleytronic and spintronic devices based on vertical heterojunctions via precise atomic-scale defect control.

The non-Hermiticity of the system gives rise to a distinct knot topology in the complex eigenvalue spectrum, which has no counterpart in Hermitian systems. In contrast, the singular values of a non-Hermitian (NH) Hamiltonian are always real by definition, meaning that they can also be interpreted as the eigenvalues of some underlying Hermitian Hamiltonian. In this work, we demonstrate that if the singular values of an NH Hamiltonian are treated as eigenvalues of prototype translational invariant Hermitian models that undergo a topological phase transition between two distinct topological phases, the complex eigenvalues of the NH Hamiltonian will also undergo a first-order knot transition between different knot structures. Unlike the usual knot transition, this transition is not accompanied by an exceptional point (EP); in contrast, the real and complex parts of the eigenvalues of the NH Hamiltonian show a discrete jump at the transition point. We emphasize that the choice of an NH Hamiltonian whose singular values match the eigenvalues of a Hermitian model is not unique. However, our study suggests that this connection between the NH and Hermitian models remains robust as long as the periodicity in lattice momentum is the same for both. Furthermore, we provide an example showing that a change in the topology of the Hermitian model implies a transition in the underlying NH knot topology, but a change in knot topology does not necessarily signal a topological transition in the Hermitian system.

Machine learning offers a promising approach to addressing the unique challenges of non-Hermitian systems, particularly in classifying topological phases and overcoming the limitations of traditional methods. However, research remains sparse for complex non-Hermitian systems involving higher-order hopping terms. In this work, we employ uniform manifold approximation and projection (UMAP), an unsupervised machine learning technique, to identify phase transition points in systems exhibiting the non-Hermitian skin effect (NHSE). Conventionally, NHSE is analyzed using non-Bloch theory, which requires redefining the Brillouin zone as the generalized Brillouin zone and solving for the complex eigenvalue contours. In contrast, our UMAP-based approach can successfully identify NHSE phase transitions in a system featuring higher-order hopping terms without relying on prior knowledge. Beyond classification, we introduce a unified framework that integrates information from three major theoretical perspectives: numerical solutions under different boundary conditions, non-Bloch theory, and Bloch theory. This framework quantitatively connects these traditionally separate and sometimes incompatible analyses. UMAP's distance metric captures the topological phase structure in a way that bypasses the need for selecting specific analytical methods or performing multiple complex computations. This approach not only circumvents the limitations of detailed analytical methods but also offers physical insights into complex topological phenomena, representing a fundamental theoretical advancement in non-Hermitian physics. We anticipate that our work will further stimulate interdisciplinary research at the intersection of physics, photonics, and artificial intelligence.

Altermagnets have recently been recognized as a distinct class of magnetic materials characterized by alternative spin-split electronic structures without net magnetization. Despite intensive studies on their single-particle spintronic and valleytronic properties, many-electron interactions and optical responses of altermagnets remain less explored. In this work, we employ many-body perturbation theory to investigate excited states and their strain tunability. Using monolayer ${\mathrm{Mn}}_2{\mathrm{WS}}_4$ as a representative candidate, we uncover a novel spin–valley-dependent excitonic selection rule in two-dimensional altermagnetic Lieb-lattices. In addition to strongly bound excitons, we find that linearly polarized light selectively excites valley-spin-polarized excitons. Importantly, these lowest-energy excitons are optically bright, making them experimentally accessible. Moreover, due to the interplay between altermagnetic spin symmetry and electronic orbital character, we predict that applying uniaxial strain can lift valley degeneracy and enable the selective excitation of spin-polarized excitons—an effect not achievable in previously studied transition-metal dichalcogenides. These generalized spin-valley-locked excitonic states and their strain tunability can offer a robust mechanism for fourfold symmetric altermagnets to encode, store, and read valley and spin information.

In a one-dimensional phthalocyanine molecular conductor $\text{TPP}{\left[\text{Fe}\left(\text{Pc}\right){\left(\text{CN}\right)}_2\right]}_2$, giant negative magnetoresistance was observed at low temperatures, where the resistivity increases. To clarify the origin of this magnetoresistance, we investigated the low-temperature insulating state, revealing a diffuse x-ray streak midway between the Bragg peaks. This suggests charge order driven by Coulomb repulsion among $\pi$-conduction electrons. The intensity increases below the temperature where the short-range antiferromagnetic order of $d$ local moments develops, which stabilizes the charge order via a Hund-like intramolecular $\pi \text{−}d$ interaction.

A density functional theory (DFT) framework is presented that links functional derivatives of free-energy functionals to nonlinear static density response functions in quantum many-body systems. Within this framework, explicit expressions are derived for various higher-order response functions of systems that are homogeneous on average, including the first theoretical result for the cubic response at the first harmonic ${\chi }_0^{(1,3)}\left(\mathbf{q}\right)$. Specifically, our framework includes hitherto neglected mode-coupling effects that are important for the nonlinear density response even in the presence of a single harmonic perturbation. We compare these predictions for ${\chi }_0^{(1,3)}\left(\mathbf{q}\right)$ to new Kohn-Sham DFT simulations, leading to excellent agreement between theory and numerical results. Exact analytical expressions are also obtained for the long-wavelength limits of the ideal quadratic and cubic response functions. Particular emphasis is placed on the connections between the third- and fourth-order functional derivatives of the noninteracting free-energy functional $F_s\left[n\right]$ and the ideal quadratic and cubic response functions of the uniform electron gas, respectively. These relations provide exact constraints that may prove useful for the future construction of improved approximations to $F_s\left[n\right]$, in particular, for warm dense matter applications at finite temperatures. Here, we use this framework to assess several commonly employed approximations to $F_s\left[n\right]$ through orbital-free DFT simulations of the harmonically perturbed ideal electron gas. The results are compared with Kohn-Sham DFT calculations across temperatures ranging from the ground state to the warm dense regime. Additionally, we analyze in detail the temperature- and wave number-dependent nonmonotonic behavior of the ideal quadratic and cubic response functions.