We show the ability of hybridizing different Rydberg states by a periodic electrostatic potential provides a conceptual scheme for engineering topological exciton structures in layered transition metal dichalcogenides. Such a potential can be remotely imprinted from charge distributions in substrate layers, whose large tunability gives rise to rich topological phase diagrams for the exciton. We find the topological lowest band of the dipolar interlayer exciton can exhibit a small bandwidth, as well as remarkable quantum geometries well suited for realizing the long-sought bosonic fractional Chern insulator. For monolayer excitons, topological bands and in-gap helical edge states can emerge near the energy of $2p$ states.

Uncovering the interfacial structures at the atomic scale is crucial for understanding and tailoring the emergent phenomena at the interfaces between nitrides and oxides. However, synthesizing high-quality interfaces with extremely large lattice mismatch and varied crystal symmetries remains a challenge. In this study, we reveal a rare interfacial coincidence structure with periodic misfit dislocations between the rocksalt nitride TiN and the perovskite oxide ${\mathrm{YAlO}}_3$, utilizing a combination of high-resolution x-ray diffraction and atomic resolution scanning transmission electron microscopy. The coincidence structure, with 3.5 units of TiN matching 4 units of ${\mathrm{YAlO}}_3$, facilitates the formation of high-quality interfaces, despite a lattice mismatch as large as $-15.4\%$ between TiN and ${\mathrm{YAlO}}_3$. Furthermore, compared the TiN films coherently grown on MgO substrates, electrical transport measurements uncover that the coincidence interface between TiN and ${\mathrm{YAlO}}_3$ with strain relaxation can lead to a higher superconducting transition temperature of 5.33 K compared to 5.02 K. Our work reveals an unconventional interfacial mechanism for forming high-quality heterostructures composed of materials with extremely large lattice mismatch. Moreover, it paves a way to tailor the electronic properties of functional layers by controlling the interfacial structures.

We examine the formation of nanoscale patterns on silicon surfaces subjected to ion beam irradiation at energies below the sputtering threshold, which suppresses net erosion. Using Kr ions with well-defined energies, we provide solid evidence that mass redistribution alone can lead to surface instability and the formation of patterns. The experimentally observed ripple structures are well described by continuum models that describe similar pattern formation processes on the surfaces of Aeolian sand dunes. This suggests that ion winds are responsible for redistributing surface atoms, forming the observed ripple patterns.

We present a scenario in which a gapless extended phase serves as a “hub” connecting multiple symmetry-enriched deconfined quantum critical points. As a concrete example, we construct a lattice model with ${\mathbb{Z}}_2^{}\times {\mathbb{Z}}_2^{}\times {\mathbb{Z}}_2^{}$ symmetry for quantum spin-1/2 degrees of freedom that realizes four distinct gapful phases supporting antiferromagnetic long-range order and one extended incommensurate gapless ferromagnetic phase. The quantum phase transition between any two of the four gapped and antiferromagnetic phases goes through either a (deconfined) quantum critical point, a quantum tricritical point, or the incommensurate gapless ferromagnetic phase. In this phase diagram, it is possible to interpolate between four deconfined quantum critical points by passing through the extended gapless ferromagnetic phase. We identify the phases in the model and the nature of the transitions between them through a combination of analytical arguments and density matrix renormalization group studies.

Cubic antiperovskite derivatives $X_3{\mathrm{BA}}_3$ feature perovskite-like structures, but with A-site anions shifted from the corners to the edge-center positions. This structural modification increases the number of atoms per unit cell compared to conventional cubic perovskites, which may result in lower lattice thermal conductivity. In this work, we systematically investigated the phonon thermal transport properties of ${\mathrm{Ba}}_3\mathrm{Bi}{X}_3$ ($X=\mathrm{Br}$, I) using first-principles calculations and Boltzmann transport theory. Our results reveal that the three-phonon lattice thermal conductivity (${\kappa }_{3\mathrm{ph}}$) of ${\mathrm{Ba}}_3{\mathrm{BiI}}_3$ ($1.81\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$) is higher than that of ${\mathrm{Ba}}_3{\mathrm{BiBr}}_3$ ($1.48\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$) at 300 K, which deviates from the expected trend based on halide atomic mass. Inclusion of four-phonon scattering corrects this trend, reducing $\kappa$ by up to 40.88% for ${\mathrm{Ba}}_3{\mathrm{BiI}}_3$ (to $1.07\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$) and 19.59% for ${\mathrm{Ba}}_3{\mathrm{BiBr}}_3$ (to $1.19\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$). The strong four-phonon scattering in ${\mathrm{Ba}}_3{\mathrm{BiI}}_3$, despite the absence of an acoustic-optical gap, is attributed to flattened optical phonon modes and pronounced anharmonicity. These factors contribute to a significantly enlarged four-phonon scattering phase space, leading to scattering strengths comparable to their three-phonon counterparts. Additionally, the wavelike (coherent) contribution is found to play a non-negligible role in the thermal transport of both compounds. These findings provide key insights into the mechanisms underlying low lattice thermal conductivity in newly reported antiperovskite derivatives and establish a promising platform for designing high-performance thermoelectric materials.

Several optical experiments have shown that in magnetic materials, the principal axes of response tensors can rotate as an odd function of an applied magnetic field. Here we offer a microscopic explanation of this effect, and we propose a closely related dc transport phenomenon—an off-diagonal symmetric conductivity, linear and odd in a magnetic field, which we refer to as linear magnetoconductivity (LMC). Although LMC has the same functional dependence on a magnetic field as the Hall effect, its origin is fundamentally different: LMC requires time-reversal symmetry to be broken even before a magnetic field is applied, and is therefore a sensitive probe of magnetism. We demonstrate LMC in three different ways: via a tight-binding toy model, a density functional theory calculation on ${\mathrm{MnPSe}}_3$, and a semiclassical treatment. The third approach identifies two distinct mechanisms yielding LMC: momentum-dependent band magnetization and Berry curvature. Finally, we propose an experimental geometry suitable for detecting LMC, and we demonstrate its applicability using Landauer-Büttiker simulations. Our results emphasize the importance of measuring the full conductivity tensor in magnetic materials, and they introduce LMC as a new transport probe of symmetry.

Magnetic long-range order in quasiperiodic lattices has rarely been observed, either in natural materials or in artificially engineered systems. In this study, we investigate a nanomagnet array based on P1 Penrose tiling and demonstrate that, within the framework of the vertex model, the system is unfrustrated, making the emergence of long-range order on quasiperiodic lattice a promising possibility. Large domains of ordered states appear following a thermal annealing protocol. However, numerous excitations also persist. Through statistical analysis, we show that the system falls out of equilibrium during the cooling process, which we attribute to a trapping effect. We further show that this trapping arises from the complex energy landscape, which obstructs the kinetic pathways necessary for the system to relax these excitations. Our findings provide important insights into the mechanisms of dynamic freezing in artificial spin ice systems.

Motivated by recent experiments, which allow for fine-tuning of the effective magnetic interaction between the impurity and the superconductor, we investigate the regime around the quantum phase transition where the ground state of the system changes from a weakly coupled free spin to a screened spin regime. At this transition, we find that the Yu-Shiba-Rusinov (YSR) states remain at finite energies at low temperatures, thereby generating a gap in the spectrum, which is inconsistent with predictions of the original YSR theory. We investigate various gap-generating scenarios and determine that the local suppression of the order parameter, only captured by self-consistent calculations, generates the gap.

We investigate the vortex flow anisotropy in the Abrikosov phase of nematic superconductors, focusing on the effects of nematic-superconducting coupling on vortex dynamics. Using numerical simulations within a time-dependent Ginzburg-Landau (TDGL) approach, we analyze vortex viscosity in a model featuring an $s$-wave superconducting order parameter coupled to an Ising-like nematic order parameter, suitable for systems with $C_4$ symmetry. Our results indicate that nematicity induces a significant anisotropy in the flux-flow resistivity, which depends on both vortex core shape anisotropy and normal-phase conductivity anisotropy. These two effects can either compete or cooperate with each other. We discuss the implications of these findings for identifying nematic superconductivity in the superconducting phase. Our work provides new insights into the interplay between nematic and superconducting order parameters, leading to new possibilities for experimental and theoretical exploration of anisotropic transport properties in unconventional superconductors.

We demonstrate that the intrinsic superconducting diode effect can affect the structure, interactions and dynamics of Abrikosov vortices in noncentrosymmetric superconductor/ferromagnet hybrid structures. The Ginzburg-Landau (GL) theory accounting for the spin-orbit and exchange-field effects predicts a chiral distortion of the superfluid velocity, noncentral interaction forces and the resulting torque in a vortex-antivortex pair, and anisotropy of the Bean-Livingston barrier. These closed-form results are fully confirmed by time-dependent GL numerical simulations carried out with a fourth-order least-squares finite-difference solver, which captures equilibrium single vortex configuration in realistic mesoscopic geometries. The analysis shows that the cubic gradient term shifts vortex cores by an amount proportional to the in-plane exchange field and simultaneously generates a lateral torque that can rotate entire vortex ensembles, showing how spin-orbit coupling and the exchange field enable breakdown of the vortex–antivortex symmetry in a finite-size sample. By combining transparent analytics with quantitative numerics, the work provides the hallmarks of vortex physics in superconducting structures with an intrinsic diode effect and supplies concrete guidelines for designing nonreciprocal superconducting circuits, fluxonic logic elements, and kinetic-inductance devices.

The presence of symmetries can lead to nontrivial dynamics of operator entanglement in open quantum many-body systems, which characterizes the cost of a matrix product density operator representation of the density matrix in tensor-network methods and provides insights into the corresponding classical simulability. One example is $\mathrm{U}\left(1\right)$-symmetric open quantum systems with dephasing, in which the operator entanglement increases logarithmically at late times instead of being suppressed by the dephasing. Here we numerically study the far-from-equilibrium dynamics of operator entanglement in a dissipative quantum many-body system with the more complicated $\mathrm{SU}\left(2\right)$ symmetry and dissipations beyond dephasing. We show that after the initial rise and fall, the operator entanglement increases again in a logarithmic manner at late times in the $\mathrm{SU}\left(2\right)$-symmetric case. We find that this behavior can be fully understood from the corresponding $\mathrm{U}\left(1\right)$ subsymmetry by considering the symmetry-resolved operator entanglement. Especially, the probability distribution of different $\mathrm{U}\left(1\right)$ sectors also follows the Gaussian distribution observed in the $\mathrm{U}\left(1\right)$-symmetric case with dephasing, with the variance growing as a power law. But unlike the latter, both the classical Shannon entropy associated with the probabilities for the half system to be in different symmetry sectors and the corresponding symmetry-resolved operator entanglement now make nontrivial contributions to the late-time logarithmic growth of operator entanglement in our $\mathrm{SU}\left(2\right)$-symmetric case. Our results show evidence that the logarithmic growth of operator entanglement at long times is a generic behavior of dissipative quantum many-body dynamics with $\mathrm{U}\left(1\right)$ as the symmetry or subsymmetry and for broader dissipations beyond dephasing, although more analytical and numerical proof from future studies is still required for this conjecture. By breaking the $\mathrm{SU}\left(2\right)$ symmetry of our quantum many-body dynamics to $\mathrm{U}\left(1\right)$, we also show that the latter property—the logarithmic growth behavior of operator entanglement for broader dissipations beyond dephasing—is valid even for open quantum systems with only $\mathrm{U}\left(1\right)$ symmetry.

We unveil an interesting example of topological flat bands of Majorana fermions in quantum spin liquids. We study the Kitaev model on a periodically depleted honeycomb lattice, under a magnetic field within the perturbation theory. The model can be straightforwardly extended while maintaining the exact solvability, and its ground state is a quantum spin liquid as on the honeycomb lattice. As fractionalized excitations, there are unpaired localized Majorana fermions in addition to the itinerant Majorana fermions and ${\mathbb{Z}}_2$ fluxes. We show that, in the absence of the magnetic field, the Majorana fermions exhibit completely flat bands at zero energy, and by applying the magnetic field, these bands turn into topological flat bands with nonzero Chern number. By varying the anisotropy of the interactions and the magnitude of the magnetic field, we clarify that the system hosts a variety of topological phases that do not appear in the original honeycomb model. We emphasize that the topological flat bands underlying this rich topology come from the hybridization of the Majorana flat bands and unpaired Majorana fermions, which is unique to the flat bands of fractionalized excitations in quantum spin liquids. Our findings would stimulate the exploration of a new class of Kitaev materials exhibiting rich topology arising from topological Majorana flat bands.

Pyrochlores host a plethora of emergent quantum phenomena such as spin ice, spin liquid, spin glass, topological phases, magnetic monopoles, etc., owing to their unique crystal structure. Here, we investigate the effect of electron doping on the magnetism of a nonmagnetic pyrochlore oxide ${\mathrm{Y}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$. Preserving the pyrochlore structure, ${\mathrm{Cr}}^{3+}\left(\mathrm{electron}\right)$ is intentionally doped up to $5\%$, which leads to a negligible increase ($<0.02\%$) in the lattice volume. Magnetization measurements reveal a systematic evolution of short-range ferromagnetism below 146 K. A deviation from the anharmonic nature of phonon frequency further validates the presence of such magnetic order. The effect of electron doping is reflected in the reduced band gap as well as enhancement of Pauli susceptibility. To understand the origin of magnetic order, doping-induced mixed valency of Ti and O vacancy is examined through XPS, density functional theory, and electron localization function. Our experimental work, in combination with theoretical analysis, demonstrates an effective way of installing ferromagnetism in nonmagnetic pyrochlores.

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 $G$.