Topologically ordered states, such as chiral spin liquids, have been proposed as candidates that host fraction alized excitations. However, detecting chiral character or proximity to these nontrivial states remains a challenge. Resonant Raman scattering can be a powerful tool for detecting chiral fluctuations, as the $A_{2g}$ channel probes excitations with broken time-reversal symmetry and local chiral order. Here, we use exact diagonalization to characterize the resonant $A_{2g}$ channel, alongside two-magnon scattering in $B_{1g}$ and $E_g$ channels, for the Hubbard model on lattices with increasing levels of geometric spin frustration, where tuning the incident energy near the Mott gap reveals strong chiral spin excitation intensity. Increased spin frustration in the Mott insulator results in an overall softening of the Raman $A_{2g}$ response, indicating a tendency toward low energy chiral-chiral fluctuations in Mott insulators with magnetic frustration and proximity to chiral spin liquid states that can potentially be tuned by external perturbations.

Binary $M_2{X}_3$ compounds ($M=\mathrm{Sb}$, Bi and $X=\mathrm{S}$, Se, Te) and their solid solutions are among the most efficient materials for thermoelectric applications near room temperature. In the canonical compound $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$, Sn has been shown to induce a resonant level (RL) ∼15 meV below the valence band edge, leading to enhanced thermopower values with respect to those achieved with rigidlike impurities. However, the question of whether Sn is still a resonant impurity in ternary alloys and notably, in the topological insulator $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_2\mathrm{Se}$, remains unsettled. Here, we demonstrate experimentally that Sn loses its resonant character in $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_2\mathrm{Se}$. Alloying with Pb in $\mathrm{B}{\mathrm{i}}_{1.99-y}\mathrm{S}{\mathrm{n}}_{0.01}\mathrm{P}{\mathrm{b}}_y\mathrm{T}{\mathrm{e}}_2\mathrm{Se}$ rigidly shifts the chemical potential towards the valence bands and reveals a metal-insulator transition at low temperatures, which can be well described by an Sn impurity level that dominates the electrical conduction up to $y=0.020$. Further increasing $y$ to 0.025 and 0.030 progressively restores a conventional valence band conduction. The presence of the Sn impurity level that forms a density-of-states peak disconnected from the valence band manifold is supported by electronic band structure calculations. Due to the quasilocalized nature of this impurity level, the addition of Sn does not enhance the thermopower values compared to those measured in Sn-free samples, resulting in comparable thermoelectric performance, with a peak $\mathit{ZT}$ value of 0.70 achieved at 425 K for $y=0.01$.

Combining graphene with transition metal dichalcogenides (TMDs) leads to enhanced spin-orbit coupling (SOC) in graphene. The induced SOC has a large effect on the low-energy part of the band structure, leading to or stabilizing topological phases or superconductivity. Here, the pressure dependence of the SOC strength is investigated in bilayer graphene/${\mathrm{WSe}}_2$ heterostructures. We performed magnetoconductance studies, such as weak localization, quantum Hall, and Shubnikov–de Haas oscillation measurements, to extract the different SOC terms which determine the low-energy band structure of bilayer graphene. We find the proximity-induced SOC strengths increased by more than 50% as a result of applying 2 GPa hydrostatic pressure. Our studies highlight the opportunity to increase the SOC coupling strength with pressure, which can be important for correlated phases or spin qubits in bilayer graphene/${\mathrm{WSe}}_2$ heterostructures.

We study the superconducting diode effect (SDE) in an Ising superconductor with broken basal mirror symmetry in a parallel magnetic field. We show that in the presence of a small Rashba spin splitting, ${\mathrm{\Delta }}_{\text{R}}$, the dominant Ising spin-orbit coupling (${\mathrm{\Delta }}_{\text{I}}\gg {\mathrm{\Delta }}_{\text{R}}$) dramatically enhances the SDE efficiency compared to a Rashba superconductor with ${\mathrm{\Delta }}_{\text{I}}=0$ and the same ${\mathrm{\Delta }}_{\text{R}}$. The suppression of the SDE for ${\mathrm{\Delta }}_{\text{I}}=0$ at ${\mathrm{\Delta }}_{\text{R}}$ much larger than the critical temperature ($T_{\text{c}}$) is accidental. At ${\mathrm{\Delta }}_{\text{R}}\ll T_{\text{c}}$, the SDE efficiency is small because, to linear order, ${\mathrm{\Delta }}_{\text{R}}$ can be removed by a gauge transformation. These two factors—the accidental suppression of the SDE at large ${\mathrm{\Delta }}_{\text{R}}$ and the systematic suppression at small ${\mathrm{\Delta }}_{\text{R}}$—are eliminated by Ising spin-orbit coupling. As a result, SDE efficiency is substantially enhanced for ${\mathrm{\Delta }}_{\text{I}}\gg {\mathrm{\Delta }}_{\text{R}}\ne 0$.

We extend the concept of conventional multiferroicity—where ferroelectric and ferromagnetic orders coexist—to include multipolar degrees of freedom. Specifically, we explore how this phenomenon emerges in $4d^2/5d^2$ Mott insulators with strong spin-orbit and Hund's couplings. Our study uncovers the origin of magnetic multipolar interactions in these systems and demonstrates that a combination of quadrupolar and octupolar magnetic order can simultaneously induce both electrical quadrupolar moments and ferroelectric polarization. By expanding the multiferroic framework to higher-order multipoles, we reveal the possibility of coexisting multipolar orders of different or same ranks, paving the way for different functional properties in a large class of strongly correlated materials.

We investigate the electric current response to axial gauge fields in noncentrosymmetric magnetic Weyl semimetals. The absence of both time-reversal and inversion symmetries allows for new types of responses. We systematically calculate the transverse, longitudinal, and Hall responses to axial gauge potentials with both linear and quadratic dispersion relations. The transverse and Hall responses are of comparable magnitude, while the longitudinal response is much smaller. Notably, with increasing frequency, the transverse and Hall response functions manifest a peak whose height is determined by the properties of Weyl fermions and is independent of the axial gauge potential. The main features of the response functions survive in the presence of disorders. As applications of our results, we propose a Hall-type magnetopiezoelectric effect, where a transverse sound wave can induce an electric current whose direction is perpendicular to the directions of sound propagation and polarization. Our results also provide a mechanism to excite magnons using electric fields and could be useful for magnon spintronics.

Polarization singularities in momentum space, encompassing bound states in the continuum (BICs) and circularly polarized states, offer significant potential for light manipulation. Prior researches have focused on the dynamic manipulation of these singularities, specifically merging BICs or spawning BICs into a pair of $C$ points. However, adjusting the geometric parameters or the tunable material can achieve just one of these outcomes. Here, we present a hybrid photonic system combining bilayer photonic crystals with tunable negative permittivity plasma, enabling the diverse manipulation of polarization singularities in momentum space, which includes generation, evolution, and annihilation of singularities by manipulating plasma permittivity without structural symmetry perturbations. We demonstrate that a symmetry-protected BIC can not only split into multiple accidental BICs and remerge with an ultrahigh $Q$ factor, but also split into a pair of $C$ points and remerge again by continuously decreasing permittivity. Furthermore, by breaking ${\delta }_z$ symmetry, multiple accidental BICs merge into a symmetry-protected BIC with controllable arbitrary ellipticity of polarization states. Importantly, the evolution of the singularities in our system covers the full Poincaré sphere, suggesting potentially applications in beam modulation and chiral optics.

Complementary media, which employ paired structures with contrasting effective parameters such as compressibility and density in acoustics, have been widely explored as an effective approach to restore wave transmission in disrupted fields. In this study, we introduce complementary Willis couplings between two-layer media that share identical effective compressibility and density. This configuration achieves acoustic field depletion (active local absorption without scattering), mimicking a shadow zone with significant attenuation while maintaining unit transmittance throughout the medium. We formulate the condition for the material parameters of the two layers to achieve such acoustic field depletion in both the reciprocal and nonreciprocal regimes. Furthermore, we experimentally demonstrate field depletion with purely nonreciprocal complementary Willis coupling facilitated by digitally virtualized active meta-atoms. Our results demonstrate that both pressure and velocity fields are minimized at the midpoint of the device but with full transmission. Unlike conventional active acoustic systems, our active material approach allows self-adaptivity to different incident waves, opening up potential applications, such as directional sensing, nonreciprocal communication, and tailored field manipulation.

Recent studies highlight the scientific importance and broad application prospects of two-dimensional sliding ferroelectrics, which prevalently exhibit vertical polarization with suitable stackings. It is crucial to understand the mechanisms of sliding ferroelectricity and to deterministically and efficiently switch the polarization with optimized electric fields. Here, applying our dream-Allegro multitask equivariant neural network, which simultaneously predicts structure-dependent interatomic potentials and Born effective charges, we construct a comprehensive model for the boron nitride $\left(\mathrm{BN}\right)$ bilayer. The molecular dynamics simulations reveal a remarkably high Curie temperature of up to 1400 K, facilitated by robust intralayer chemical bonds and delicate interlayer van der Waals interactions. More importantly, it is found that, compared to the out-of-plane electric field, the inclined field not only leads to deterministic switching of electric polarization, but also largely lowers the critical strength of the field, due to the presence of the in-plane polarization in the transition state. This strategy of an inclined field is demonstrated to be universal for other sliding ferroelectric systems with monolayer structures belonging to the symmetry group $p\overline{6}m2$, such as transition metal dichalcogenides.

Topological textures, which refer to nontrivial vector field configurations with topological protection in real space, have aroused great interest in various physical branches. However, conventional topological textures are achieved under stringent excitation conditions that solely hosted a single symmetry configuration in a designed metastructure. Here, we propose a subwavelength acoustic Mie resonator to support localized skyrmion and meron lattice modes for velocity field vectors on structure surface simultaneously depending on the excited location of the point source. We theoretically analyze and numerically calculate the near-field distribution of Mie resonating modes, and find that the higher-order monopole modes correspond to Néel type skyrmion modes, while the multipolar resonating modes belong to meron lattice modes consisting of symmetrically distributed merons and antimerons on the structure surface along the azimuthal direction. We also experimentally observe the near-field distribution of velocity vectors to verify the skyrmions and merons on the structure surface, and the topologically protected property is demonstrated by introducing the structure defects. Multitype topological textures can be simultaneously excited on a subwavelength Mie resonator without strict excitation conditions, which may be a versatile platform for encoding information in versatile topological textures.

Using first-principles calculations, we systematically investigate the spin contributions to the inverse Faraday effect (IFE) in transition metals. The IFE depends on the $d$-electron filling and asymmetry between excited electron and hole spin moments. Our results reveal that even elements with smaller electron magnetic moments, such as Os, can exhibit higher IFE due to greater electron-hole asymmetry. Pt shows the highest IFE in the $1–2\mathrm{eV}$ frequency range, while Os dominates in the $2–4\mathrm{eV}$ range. In addition, we demonstrate that the IFE of neighboring elements with similar crystal structures (e.g., Ir, Pt, and Au) can be tuned by adjusting their Fermi levels, indicating the importance of $d$ electron filling on IFE. Finally, we find that the trend in electron (or hole) contributions to the IFE closely follows that of the spin-Hall conductivity; however, the total IFE involves more complex interactions.

The influence of the superconducting transition on the Casimir effect remains experimentally elusive. We propose an approach to address this challenge, exploiting the first-order superconducting transition induced in a thick film by a parallel magnetic field. Our calculations for a Au sphere opposite a Pb film, based on the Mattis-Bardeen theory, predict a jump in the Casimir force across the transition. By periodically modulating the magnetic field, we induce a corresponding modulation of the Casimir force that should be readily detectable with existing microtorsional oscillator technology, opening a promising pathway to finally observe the long-sought Casimir-superconductivity coupling. A successful measurement of this effect would provide crucial insights into the fundamental nature of the Casimir force and its interaction with macroscopic quantum phenomena.

The Hopf-Chern insulator is an unconventional three-dimensional topological insulator with a bulk gap and gapless boundary states without protection from global discrete symmetries. This study investigates its fate in the presence of local magnetic and charge impurities. We find it stable up to moderate disorder values by analyzing the surface states and the zero energy bulk density of states using large-scale numerical simulation and the self-consistent Born approximation. The disordered Hopf-Chern insulator shows reentrant behavior: the disorder initially expands the topological phase before driving it across an insulator-diffusive metal transition. We examine the associated critical exponents via finite-size scaling of the bulk density of states, participation entropy, and two-terminal conductance. We estimate the correlation length exponent $\nu \simeq 1.0\left(1\right)$, consistent with the clean two-dimensional Chern universality and distinct from the integer quantum Hall exponent.

Accurate prediction of infrared dielectric functions in polar materials is fundamental for thermal and photonic applications, yet it remains unexplored whether the two main methods, the Green-Kubo formula and Lorentz model, can give unified predictions. In this work, we present a detailed comparison of these two approaches using MgO and LiH as prototypical cases employing both the empirical rigid ion model (RIM) and machine learning potential (MLP). We demonstrate that the conventional Lorentz model fails to capture the multiphonon absorption inherent in the Green-Kubo method, which can be resolved using the phonon self-energy as a generalization of the usual linewidth. In addition, with RIM, a correction factor of ${\varepsilon }_{\infty }$ is required in the ionic contribution to the infrared response to account for the electronic polarization effect, which is yet captured by MLP using the Born effective charges for calculating the dipole moment. The present benchmark study thus enables cross-validation of dielectric function calculations while providing mechanistic insights into the polarization dynamics.

This paper presents a quantum field theoretical formalism for studying magnons in finite nanostructures with arbitrary shapes and spatially nonuniform ground states. It extends the classical micromagnetic formalism by introducing a micromagnetic Hamiltonian quantum operator, which incorporates exchange, Dzyaloshinsky-Moriya, anisotropy, magnetostatic, and Zeeman energies. The nonuniformity of the ground state is handled by locally aligning the quantization axis of the magnetization field operator with the classical ground state. The Hamiltonian is expanded in the large spin-number limit and truncated to retain only terms quadratic in the components of the magnetization operator transverse to the quantization axis. This quadratic Hamiltonian is used to derive the linear quantum Landau-Lifshitz equation. By diagonalizing this equation under appropriate boundary and normalization conditions, a discrete set of magnon creation and annihilation operators is obtained, enabling a complete description of the magnon spectrum. Finally, the theory is applied to study the effects of temperature and shape on low-temperature thermal equilibrium fluctuations of magnons in thin ferromagnetic nanodisks.

We present a comprehensive muon spin relaxation/rotation (μ$\mathrm{SR}$) study of the ${\mathrm{Co}}^{2+}$-based alternating Heisenberg $J_{\text{eff}}=\frac{1}{2}$ spin chain system ${\mathrm{Sr}}_2\mathrm{Co}{\left({\mathrm{SeO}}_3\right)}_3$. Low-temperature magnetic property measurements confirm a spin-singlet ground state and identify two critical fields, $H_{\text{C1}}$ and $H_{\text{C2}}$. At $H_{\text{C1}}$, the system evolves from the spin-singlet state to a canted antiferromagnetic phase, which persists up to $H_{\text{C2}}$, where the system enters a fully polarized state. This magnetically ordered phase exists between μ${}_0{H}_{\text{C1}}^{\perp c}=2$ T and μ${}_0{H}_{\text{C2}}^{\perp c}=3.05$ T for μ${}_{0}H\perp c$ and between μ${}_0{H}_{\text{C1}}^{///c}=2$ T and μ${}_0{H}_{\text{C2}}^{///c}=3.6$ T for $H//c$, reflecting the presence of anisotropy. Additionally, μ$\mathrm{SR}$ results provide insights into the thermal and field evolution of spin dynamics, revealing a thermal crossover in spin correlations, the reopening of a spin gap due to anisotropy above $H_{\text{C1}}$, and the emergence of a magnon gap above $H_{\text{C2}}$. These findings imply the suppressed criticality of the canted antiferromagnetic phase by anisotropy. Our study establishes ${\mathrm{Sr}}_2\mathrm{Co}{\left({\mathrm{SeO}}_3\right)}_3$ as a model system for investigating field-driven quantum phase transitions in one-dimensional $J_{\text{eff}}=\frac{1}{2}$ quantum spin chains with anisotropy.

We explore theoretically the properties of engineered bimetallic nanostructured superlattices where an array of nanoclusters of a simple (single band) metal are embedded periodically inside another simple metal with a different work function. The exploration is done using a simplified tight-binding model with Coulomb interactions included, and also density functional theory. Taking arrays of Ag clusters of fixed sizes and configurations (when unrelaxed) embedded periodically in a Au matrix as an example, we show that a significant enhancement of electron-phonon interactions ensues, implying possibilities for high-$T_c$ superconductivity. The enhancement stems from a strong coupling, via Coulomb interactions, between the dipolar charge distribution that forms at the Au-Ag interfaces and the breathing and other modes of vibration of the light Ag atoms caged inside the heavier Au matrix. The interface dipoles form because of the interplay between the mismatch of the local potential seen by the conduction electrons localized in Wannier orbitals at the Ag and Au sites (the Ag sites being slightly repulsive relative to the Au sites) and the (long-range) Coulomb repulsion between electrons occupying these Wannier orbitals. We also discuss the DC transport in such systems.