We study the high-frequency permeability of the composite materials consisting of hollow ferromagnetic particles embedded into the nonmagnetic media. We model the ferromagnetic particles in composite by spherical shells: the thickness of the ferromagnetic region $d$ compared to the particles' diameter $D$ can vary in a wide range, from $d\ll D$ to $d\sim D$. We assume that the magnetization distribution in such a particle is nonuniform, but forms a vortexlike structure: the magnetization is twisted in some plane outside two vortex cores placed at the poles of the particle. We consider two types of magnetic anisotropy, which help to stabilize such a magnetic configuration: the easy-plane magnetic anisotropy and the “circular” uniaxial magnetic anisotropy with easy axis rotated together with the magnetization direction outside the vortex core. The high-frequency permeability of such a composite material has been studied in the limit of noninteracting particles. We study the dependence of the permeability on the ratio $d/D$. We showed that for $d\sim D$, the composite's permeability behaves in a similar manner for both types of magnetic anisotropy. It was also shown that for the second type of magnetic anisotropy and in the limit $d/D\ll 1$, the frequency dependence of the particle's susceptibility is quite similar to that for the thin film. At the same time, the magnetization oscillations in the ac field are nonhomogeneous for both types of anisotropy.

Rare-earth containing wide band gap oxides, which provide spin-photon interface and narrow linewidth optical emission, are getting significant attention as the most promising candidate materials in advancing quantum transduction and memories. Here, from ab initio calculations, we identify antiferromagnetic ground states in structurally preferred monoclinic ${\mathrm{CePO}}_4$ and tetragonal ${\mathrm{CeVO}}_4$ exhibiting localized occupied and unoccupied Ce $4f$ states with $4f\text{−}4f$ transition characteristics. Interestingly, in ${\mathrm{CePO}}_4$, O $2p$ and P $3p$ states hybridize negligibly with Ce $4f$ states, while in ${\mathrm{CeVO}}_4$, V $3d$ and O $2p$ states hybridize and appear as extended states in between the occupied and unoccupied Ce $4f$ states. Here, phonon calculations and analysis identify and differentiate Raman active phonon modes along with the spin phonon coupling of Ce in both ${\mathrm{CePO}}_4$ and ${\mathrm{CeVO}}_4$ that ultimately lead to different $4f$ ground-state crystal-field multiplets, which are critical to accurately describe electronic transitions for foundational quantum transduction and memories. Further, the identified $C_1$ site symmetry of Ce, lacking inversion symmetry in ${\mathrm{CePO}}_4$, is relevant for quantum memories and $D_{2d}$ site symmetry of Ce exhibiting inversion symmetry in ${\mathrm{CeVO}}_4$ is relevant for quantum transduction.

We consider a one-dimensional multiorbital Kondo lattice model and show that by tuning the kinetic energy of the itinerant electrons, it is possible to stabilize Kondo insulators with nontrivial spin physics. In particular, depending on the size of the exchange coupling between the local moments, we find kinetic-energy-driven transitions between a featureless Kondo insulator and a valence-bond solid or a gapless spin liquid. We also provide evidence for an unconventional continuous phase transition between two featureless Kondo insulators distinguished by their quantum numbers under reflection symmetry. At the corresponding critical point, the system is compressible, exhibits algebraic spiral spin correlations, and shows infrared behavior that is not captured by the standard conformal field theory framework.

Heusler alloys, renowned for their multifunctionality and capacity for vast elemental customization, are primarily classified into half-Heusler (XYZ) and full-Heusler (${\mathrm{X}}_2\mathrm{YZ}$) structural types. Typically, the 18-electron half-Heusler and the 24-electron full-Heusler alloys are recognized as semiconductors, following the Slater-Pauling rule. Semiconductors are desired for many applications, but they represent a minor portion compared to the predominantly metallic and half-metallic members of the Heusler family. Recently, vacancy-filling off-stoichiometric Heuslers of ternary ${\mathrm{X}}_{1+\beta }\mathrm{YZ}$ ($0\le \beta \le 1$) and quaternary ${\mathrm{X}}_{\alpha }{{\mathrm{X}}^{\prime }}_{\beta }\mathrm{YZ}$ ($1\le \alpha +\beta \le 2$) have emerged as a versatile strategy to broaden the scope of Heusler semiconductors. However, the flexibility associated with off-stoichiometry inevitably leads to complications, including issues with fractional filling ratios and complex site occupations. This work presents a comprehensive landscape of transition metal-containing Heusler semiconductors, focusing on the off-stoichiometric Heuslers but seamlessly encompassing the integer-stoichiometric systems. The structural and electronic properties can be theoretically understood through a few simple rules. Many systems have been experimentally validated, showcasing their potential for applications such as thermoelectric converters.

Massless Dirac particles are characterized by an effective pseudospin-momentum locking, which is the origin of the peculiar scattering properties of Dirac particles through potential barriers. This pseudospin-momentum locking also governs the quantum geometric properties (such as the Berry phase and Berry curvature) of Dirac particles. In the present work, we demonstrate that a domain wall separating two regions with distinct quantum geometric properties can serve as an alternative to potential barriers. Specifically, using the three-band $\alpha -T_3$ model of two-dimensional Dirac particles, we show that a Berry phase domain wall results in partial reflection and transmission of the Dirac particles, despite the fact that the incident and refracted momenta are identical.

Here, we present experimental measurements probing the influence of crystallization and surface oxidation on the Casimir force from ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ (GST225) thin films, highlighting the effects of material state and environmental exposure on fluctuation-induced interactions. Using an Au-coated microsphere attached to a cantilever of an atomic force microscope, the Casimir force was measured above amorphous and crystalline GST225 thin films in a nitrogen-purged chamber following vacuum evacuation to minimize surface contamination and moisture that lead to strong capillary forces. Crystallization of the amorphous GST225 films led to a consistent increase in the measured Casimir force by approximately 40% at surface separations less than 100 nm, which is attributed to higher optical reflectivity and dielectric contrast spanning the infrared to visible-UV spectral range. In contrast, prolonged exposure to ambient air reduced the force by 20–30%, because of oxidation-induced changes in surface composition and dielectric function, as verified by transmission electron microscopy and spectroscopic ellipsometry. Therefore, both the phase state and surface chemistry significantly influence Casimir interactions from GST225 thin films, offering insights into material-dependent fluctuation forces relevant to nanoscale device environments.

In this article, we employ the transfer matrix method to investigate relativistic particles in a superperiodic potential of arbitrary order $n$, with $n$ a positive integer. We calculate the reflection and transmission probabilities for the spinless Klein particle encountering rectangular potential barriers with superperiodic repetition. It is found that spinless relativistic particles exhibit Klein tunneling and a significantly higher degree of reflection compared to their nonrelativistic counterparts. Additionally, we analytically explore the behavior of the experimentally realizable massless Dirac electrons as they encounter rectangular potential barriers with a superperiodic pattern in a monolayer of graphene. In this system, the transmission probability, conductance, and Fano factor are evaluated as functions of the number of barriers, the order of superperiodicity, and the angle of incidence. Our findings reveal that the transmission probability shows a series of resonances that depend on the number of barriers and the order of superperiodicity. We extend our analysis to specific cases within the unified Cantor potential $\gamma$ system ($\gamma$ is a scaling parameter greater than 1), focusing on the general Cantor potential (GCP) and the general Smith-Volterra-Cantor (GSVC) system. For the GCP, we calculate the tunneling probability, which reveals sharp transmission peaks and progressively thinner single-cell potential as $G$ increases. In the GSVC system, we analyze the potential segment length and tunneling probability, observing nearly unity tunneling coefficients when $\gamma \approx 1$, as well as saturation behavior in transmission coefficients at higher stages $G$.

Lead-free vacancy ordered double perovskite materials are of interest in photovoltaic field from their excellent stability and long carrier lifetime. However, the consequences of the spin-orbit coupling (SOC) induced Rashba effect on the photovoltaic performance are not well understood. Herein, the SOC inducing spin carrier dynamics of ${\mathrm{Cs}}_2{\mathrm{SnBr}}_6\text{/}{\mathrm{PdS}}_2$ heterostructure are investigated through density functional theory (DFT) and ab initio nonadiabatic molecular dynamics (NAMD) with SOC simulation. It has been found that the ${\mathrm{Cs}}_2{\mathrm{SnBr}}_6\text{/}{\mathrm{PdS}}_2$ heterostructure exhibits Rashba effect due to symmetry breaking. The electronic and spin properties of ${\mathrm{Cs}}_2{\mathrm{SnBr}}_6\text{/}{\mathrm{PdS}}_2$ heterostructure are tunable via applying pressure, resulting in Rashba spin-splitting. As pressure increases, the heterostructure exhibits stronger Rashba effect, which Rashba constant ${\alpha }_{\mathrm{R}}$ for conduction band minimum and valence band maximum are $0.055$ and $0.497\mathrm{eV}\text{/}\AA$ under 9 GPa. Based on DFT and NAMD calculations, we demonstrate that the carrier recombination rate is reduced due to mismatch spin-states and electron-phonon coupling larger than SOC values, resulting in spin-forbidden path. The carrier lifetime enhancement factor is linear with the pressure inducing Rashba effect magnitude. The proposed spin carrier transfer mechanism is important for understanding the fundamental physics in perovskite materials and for designing perovskite-based solar cells with better performance.

Scandium nitride, an emerging rocksalt indirect bandgap semiconductor, has attracted much interest recently for thermoelectricity, infrared plasmon and phonon-polaritons, neuromorphic computing, and Schottky diode device applications. As-deposited ScN thin films exhibit a high electron concentration due to oxygen impurities and nitrogen vacancies. Magnesium hole doping is the only effective method to compensate for high electron concentration and achieve $p$-type ScN. However, it is crucial to identify other hole doping strategies for ScN to promote its diverse applications. Here, we show conclusive experimental evidence of ion-implanted carbon as a hole dopant in ScN, reducing electron concentration by more than an order of magnitude. Through comprehensive spectroscopic and microscopic characterization techniques and first-principles modeling, we show that carbon occupies nitrogen sites in ScN for low dopant concentrations, leading to a hole-doping nature that compensates for ScN's high electron concentration. However, as carbon concentration increases, its hole doping ability reduces due to the formation of donor-type defect complexes identified from first-principles modeling analysis. Our work marks the experimental demonstration of hole doping in ScN with carbon ion-implantation and presents a pathway to tune the electron concentration in ScN for device applications.

We show that in systems with highly degenerate energy spectra, such as the two-dimensional transverse-field Ising model (2DTFIM) in the strong-field limit, quantum chaos can emerge in finite systems for arbitrary small perturbations. In this regime, the presence of extensive quasiconserved quantities can prevent finite systems from becoming ergodic. We study the ensuing crossover to ergodicity in a family of models that includes the 2DTFIM, in which the onset of ergodic behavior exhibits universality and occurs for perturbation strengths that decrease polynomially with increasing system size. We discuss the behaviors of quantum chaos indicators, such as level spacing statistics and bipartite entanglement, and of the fidelity susceptibilities and spectral functions across the crossover.

We investigate the effects of hydrostatic pressure on $\alpha \text{−}{\mathrm{RuCl}}_3$, a prototypical material for the Kitaev spin model on a honeycomb lattice with a possible spin-liquid ground state. Using ultrasound measurements at pressures up to 1.16 GPa, we reveal significant modifications of the acoustic properties and the $H\text{−}T$ phase diagram of this material. Hydrostatic pressure suppresses the three-dimensional magnetic order and induces a dimerization transition at higher pressures. At low pressures, the sound attenuation exhibits a linear temperature dependence, while above 0.28 GPa, it becomes nearly temperature independent, suggesting a shift in the phonon scattering regime dominated by Majorana fermions. These findings provide new insights into spin-strain interactions in Kitaev magnets and deliver a detailed characterization of the $H\text{−}T$ phase diagram of $\alpha \text{−}{\mathrm{RuCl}}_3$ under hydrostatic pressure.

This study explores the structural and magnetic properties of as-deposited ${[\mathrm{Gd}\left(4\mathrm{nm}\right)/\mathrm{Fe}\left(t\mathrm{nm}\right)]}_{\times 10}$ multilayers, with $t=2.0,2.5$, and $3.0\mathrm{nm}$. Structural characterization was carried out using both laboratory-based and synchrotron-based x-ray techniques. X-ray reflectivity (XRR) measurements indicate the formation of a GdFe alloy at the interfaces for elevated Fe thickness, suggesting significant interfacial intermixing during deposition. Magnetic properties were investigated using the magneto-optical Kerr effect (MOKE), bulk magnetization measurements, and simulations based on a modified Stoner-Wohlfarth model for a one-dimensional spin chain. The structural and magnetic properties suggest the formation of superparamagnetic Fe clustering at room temperature for the lower Fe thickness sample. Magnetic measurements reveal a distinct evolution from a Gd dominated phase to Fe dominated phase with increasing Fe layer thickness, with the intermediate sample showing both Gd and Fe aligned phase across temperature. Simulations, incorporating inputs from structural measurements, successfully reproduce the evolution of hysteresis loops with temperature and Fe thickness. The simulations provide layer-resolved insights into spin configurations, elucidating the formation of twisted/fan-like magnetic states due to the competition between antiferromagnetic exchange coupling and the external field across varying temperatures. Our results also reinforce the fact that the interfacial alloying significantly decreases the compensation temperature of the system.

We report large-scale atomistic simulations of inhomogeneous polar textures in ${\mathrm{PbTiO}}_3$ using a recently developed open-source second-principles effective interatomic potential. The model is meticulously validated against density functional theory, reproducing structural, energetic, and dynamical properties, which ensures predictive reliability beyond the training set. Building on this foundation, we uncover and characterize a rich variety of polar configurations, including Bloch-type domain-wall transition, Ising lines, skyrmions, skyrmioniums, target skyrmions, skyrmion bags in free bulk, as well as antiskyrmions, merons, and antimerons under biaxial tensile strain. These results broaden the known landscape of ferroelectric topologies and highlight ${\mathrm{PbTiO}}_3$ as a versatile host for emergent polar textures with potential applications in functional devices. The open-source model provides the community with a robust and efficient tool for exploring complex ferroelectric phenomena at large scales.

The flexible control of wave transport in three-dimensional (3D) space has long been a challenge. Here, we take advantage of the 3D linear dispersion of Weyl nodes and design a sandwiched valley-Hall crystal for robust acoustic waveguide transport. On the grounds of negligible intervalley scattering, such transport is valley locked and the waveguide shape can be altered in an arbitrary way. We experimentally validate such Weyl-node-based 3D topological transport by fabricating and characterizing a phononic crystal, and robust transmission for distinctive waveguide configurations has been observed. Our work introduces different avenues for implementing 3D valley-locked transport and offers a platform for topological device design.

Rare-earth triangular-lattice magnets serve as an excellent platform for investigating exotic quantum magnetic phenomena. Recently, the hexaaluminate ${\mathrm{CeMgAl}}_{11}{\mathrm{O}}_{19}$ has been proposed to host a $U\left(1\right)$ Dirac quantum spin liquid state with dominant Ising anisotropy. Here, we report a systematic study of its analog, ${\mathrm{NdZnAl}}_{11}{\mathrm{O}}_{19}$, employing ac susceptibility, inelastic neutron scattering, and muon spin relaxation measurements. Inelastic neutron scattering measurements establish a well-defined $J_{\mathrm{eff}}=1/2$ ground state with moderate Ising anisotropy ($g_c=4.54, g_{\mathrm{ab}}=1.42$). Muon spin relaxation measurements reveal persistent fluctuations emerging below $\sim 15$ K, and extending down to at least 0.28 K. The ac susceptibility data further indicate an absence of magnetic ordering or spin freezing down to 50 mK, despite an overall antiferromagnetic interaction with a Curie-Weiss temperature of $-0.42$ K. These results suggest that ${\mathrm{NdZnAl}}_{11}{\mathrm{O}}_{19}$ is a good candidate material for realizing a quantum spin liquid state.

We report on the interplay between atomic-scale inhomogeneity and competing magnetic phases and their effect on the anomalous Hall effect in the layered antiferromagnet ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$, a natural superlattice hosting coexisting ferromagnetic and antiferromagnetic phases. Using a combination of scanning tunneling microscopy (STM), DC and AC magnetization, and magnetotransport measurements, we reveal that intrinsic Mn–Bi antisite defects induce strong interlayer exchange coupling, giving rise to a robust exchange bias observed in both magnetic and Hall responses. The exchange bias undergoes a transition from asymmetric to symmetric behavior between 2 and 6 K, indicating a temperature-driven dynamical reconfiguration of interfacial spin structures. The training effect analysis revealed a stronger contribution of frozen spins at 2 K compared to 6 K, with relaxation amplitude shift from $-264$ to $+306$ Oe. This sign reversal indicates a field-induced change in interfacial coupling. The temperature dependence of longitudinal resistivity (${\rho }_{xx}$) and magnetization reveals complementary behavior, indicating the coexistence of two distinct spin states near the magnetic transition temperature. The phase-fraction-based resistivity model captures the distinct scattering mechanisms that govern electronic transport across different magnetic regimes. Our findings offer a direct link between microscopic disorder, interfacial magnetism, and macroscopic topological phenomena in magnetic topological insulators.

We develop a phenomenological theory describing the interaction of superconducting condensate with a Bessel beam of twisted light characterized by a nonzero angular momentum $m$. Starting from the time-dependent Ginzburg-Landau model with the complex relaxation time, we calculate the spatial profiles of dc photoinduced currents and magnetic fields as well as the second harmonic response. The photocurrents and magnetic fields are shown to be determined both by the helicity of light and its orbital momentum $m$. Analyzing the half-space and thin film geometries, we discuss possible experimental tests aimed to probe the superconducting photocurrents and magnetic fields.

We report the discovery of a multicritical point that extends the liquid-gas paradigm to systems with competing symmetry-breaking orders. Using large-scale Monte Carlo simulations of a frustrated bilayer Ising antiferromagnet with tunable couplings, we map out a rich finite-temperature phase diagram hosting three ordered phases separated by both continuous and first-order transitions. By tuning the couplings, a tricritical line and a critical end-point line converge into a single multicritical line. At all points along the multicritical line, symmetry-distinct phases exhibit identical leading critical behavior—consistent with the tricritical Ising universality class—while the subleading exponent exhibits a sharp shift from $y_g=0.8$ to $y_g=1$. This shift reflects an emergent $Z_2$ symmetry akin to that of the liquid-gas critical point, but realized here at a genuine multicritical point involving simultaneous microscopic symmetry breaking. Our results establish a universality scenario in which emergent symmetry preserves the leading class but reorganizes subleading scaling, providing a general mechanism for symmetry-enforced multicriticality.

The designed heterostructure of two experimentally synthesized and theoretically studied double perovskites ${\mathrm{Sr}}_2{\mathrm{CeIrO}}_6$ and ${\mathrm{Sr}}_2{\mathrm{MgIrO}}_6$ is investigated using the electronic structure method of the first-principles density functional theory. A half-metallic electronic structure is observed originating from the interfacial Ir site, in contrast to the insulating state that was found in the bulk ingredients. Further, we obtain an AFM ground state which is also supported by the microscopic magnetic exchange interactions analysis. The electronic and magnetic interactions are highly anisotropic in nature. The metallic transport is significantly larger at the in-plane interface layer as compared to that of the out-of-plane, and further shows the signatures of the formation of a two-dimensional (2D) Fermi gas. The impact of spin-orbit coupling (SOC) is crucial as it opens up a pseudogap at ${\mathrm{E}}_F$. Our study also reveals the variation in the impact of SOC for the different layers of Ir present in the heterostructures. Our results influence the understanding of the device engineering utilizing the anisotropic transport at the confined 2D interface in the presence of strong SOC physics.