We report carbon doping modulation of interface magnetic anisotropy and Dzyaloshinskii-Moriya (DM) interaction in the Co/Pt multilayers with different Co sublayer thicknesses. A doping-driven spin reorientation transition (SRT) in Co/Pt multilayers was demonstrated. The separation of bulk and interface magnetic anisotropy revealed that the carbon doping preferentially disrupted the Co/Pt interface. The existence of DM interaction is confirmed by the anomalous Hall effect and Brillouin light scattering spectroscopy measurements. The competition between the perpendicular magnetic anisotropy and the DM interaction induces the domain transition from droplet to dendritic domain, which is observed by a polar magneto-optical Kerr effect microscope and reproduced by micromagnetic simulations with material-specific parameters. First-principles calculations are used to understand the doping-driven SRT. The lattice volume variation of the Co sublayer and the increase of average interlayer spacing $d$ are responsible for the bulk and interface magnetic anisotropy reduction, respectively. This work establishes doping with metalloid elements as an effective approach for significant modulating magnetism in multilayers and provides insights for designing potential spintronic materials via doping-engineered magnetic properties.

The orbital Hall effect (OHE) has attracted intensive studies recently due to its potential for substantially enhancing spin-orbit torque (SOT) generation, which is essential for the SOT-induced magnetization switching in spintronic devices. In this work, we report highly efficient SOT-driven magnetization switching in nonmagnet (NM)/CoPt bilayers, enabled by a pronounced OHE in NM and substantial orbital-to-spin conversion within the CoPt ferromagnet. The critical current density for the magnetization switching in a Ti/CoPt device is reduced by an order of magnitude compared to that in a CoPt single layer. Correspondingly, SOT efficiency measurements reveal an enhancement by one order of magnitude in Ti/CoPt relative to CoPt alone. This enhancement is attributed to the large OHE in Ti rather than its negligible spin Hall effect. The orbital current generated in Ti is injected into CoPt and then converted into spin current via strong spin-orbit coupling in CoPt. Our findings pave the way for leveraging orbital current to further amplify the efficiency of magnetization switching in spintronic devices.

Unconventional superconductivity (SC) featuring multifermion orderings has attracted significant attention. However, previous studies have primarily focused on two-dimensional (2D) systems or 3D systems with effective 2D symmetries. Here, we explore the vestigial phases arising from thermal fluctuations of chiral SC in 3D systems governed by the cubic $O_h$ point group. By constructing low-energy effective Hamiltonians via Ginzburg-Landau analysis and conducting Monte Carlo simulations, we systematically analyze the phase fluctuations of chiral orders within the $E_g$ and $T_{2g}/T_{1u}$ irreducible representations (IRRPs). We identify a phase diagram topology distinct from its 2D counterparts, where the multiphase intersection manifests as a tetracritical point rather than the triple point typically found in 2D systems. Our findings reveal that, for both the $E_g$ and $T_{2g}/T_{1u}$ IRRPs, the primary chiral orders melt into a chiral metallic phase within specific parameter regimes. Furthermore, for the $E_g$ IRRP, phase fluctuations induce a charge-$4e$ phase, while for the $T_{2g}$ and $T_{1u}$ IRRPs, they lead to a higher-order charge-$6e$ SC state. Ultimately, our work highlights the role of nontrivial 3D crystalline symmetries in driving exotic vestigial orders.

The anomalously high fluorine ionic diffusivity reported in ${\mathrm{CaF}}_2\text{−}{\mathrm{BaF}}_2$ multilayer ultrathin heterostructures at around 600 K more than two decades ago [N. Sata et al., Nature (London) 408, 946 (2000)] has remained unresolved due to the complex distribution and diffusion behavior of vacancies and interstitials at the interface. Here, we address this long-standing issue by employing a cluster expansion model combined with machine-learning molecular dynamics, enabling atomic-level analysis of fluorine ion thermodynamics and kinetics. We find that fluorine vacancies preferentially accumulate at the ${\mathrm{CaF}}_2$-side interface, whereas fluorine interstitials appear only on the ${\mathrm{BaF}}_2$ side. At 600 K, diffusion is dominated by interstitial-mediated fluorine diffusion in the ${\mathrm{BaF}}_2$ region, whereas at 900 K vacancy-mediated fluorine diffusion on the ${\mathrm{CaF}}_2$ side becomes active, and the coexistence of both mechanisms leads to a synergistic enhancement of the overall diffusivity. The spatial separation of defect distributions and diffusion pathways arises from the coupling between electronic stabilization and asymmetric interfacial strain. Electron pairing between trapped electrons in adjacent ${\mathrm{V}}_{\mathrm{F}}\mathrm{s}$ stabilizes ${\mathrm{V}}_{\mathrm{F}}$ clustering at the ${\mathrm{CaF}}_2$-side interface, whereas tensile strain on the ${\mathrm{BaF}}_2$ side enlarges octahedral interstitial sites and promotes interstitial-mediated fluorine hopping; conversely, compressive strain on the ${\mathrm{CaF}}_2$ side suppresses interstitial occupation. These findings provide microscopic insight into the origin of the anomalous diffusion and clarify how electronic stabilization of vacancy clustering and local strain modulation of interstitial formation jointly regulate defect distributions and diffusion mechanisms in fluorite-structured heterostructures.

The utilization of terahertz (THz) emission spectroscopy in femtosecond photoexcited spintronic heterostructures has emerged as a versatile tool for investigating ultrafast spin transport in a noncontact and noninvasive manner. However, the investigation of ultrafast orbital transport is still in the primitive stage. Here, we experimentally demonstrate the orbital-to-charge current conversion in Co/Ru heterostructures and identify signatures that cannot be consistently explained within a conventional spin-current framework. Time-domain measurements reveal delayed and broadened THz waveforms with increasing Ru thickness, suggesting the presence of long-range angular momentum transport associated with orbital contributions. In Co/Pt/Ru trilayers, the THz emission is further enhanced through cooperative effects between the inverse spin Hall effect (ISHE) in Pt and inverse orbital Hall effect (IOHE) in Ru, where collinear charge currents are generated and add constructively. In contrast, reversed stacking configurations exhibit suppressed emission, highlighting the critical role of stacking sequence and interface-controlled transmission. Ferromagnetic resonance (FMR) measurements reveal a strong correlation between damping and THz amplitude, highlighting efficient angular momentum conversion. These results position Co/Ru as a promising orbitronic platform for tunable ultrafast THz emission. Our results not only strengthen the physical mechanism of condensed matter physics but also pave the way for designing promising spin-orbitronic devices and THz emitters.

As an emerging magnetic phase, altermagnets (AMs) with collinear compensated magnetism in real space and alternating spin splitting in the band structure have attracted widespread attention. Here, based on first-principles calculations, we demonstrate that the layer stacking imposes symmetry constraints on the spin and valley degrees of freedom (DOFs) in bilayer systems composed of two tetragonal altermagnetic monolayers, thereby enabling the tuning of these DOFs through interlayer sliding as well as by an external electric field. Using several representative AM systems, we reveal that the $\left[C_2\left|\right|\mathcal{P}\right]$ and $\left[C_2\left|\right|{\mathcal{M}}_{\mathcal{z}}\right]$ symmetries intrinsically enforce spin degeneracy, while the coupling between spin and layer DOFs enables spin-state tuning through the relative alignment (parallel or antiparallel) of the Néel orders in the two monolayers or by an external electric field. Appropriate interlayer sliding breaks the $\left[C_2\left|\right|{\mathcal{M}}_d\right]$ symmetry, thereby giving rise to valley splitting. Depending on whether these symmetries are preserved, stacking configurations generated by interlayer sliding can be classified into distinct magnetic states, enabling a unified description of spin and valley behaviors. Owing to the stacking-dependent spin and valley splitting, enhanced tunneling magnetoresistance can be realized in AM systems. This work highlights the intrinsic correlation among spin, valley, and layer DOFs, offering symmetry-based design principles for layer-based spintronic and valleytronic devices.

Achieving precise and nonvolatile electrical control of spin represents a fundamental yet long-standing challenge in spintronics. In this work, we demonstrate that bilayer altermagnets with sliding ferroelectricity give rise to a distinct form of sliding multiferroicity, thereby establishing a pathway for precise and nonvolatile electrical spin manipulation. Through a combination of symmetry analysis and first-principles calculations, we identify bilayer Ca(CoN)${}_2$ as a representative system, in which sliding between layers reconstructs the stacking order and switches the spontaneous polarization with an ultralow energy barrier. Unlike conventional gate-controlled schemes, the spin-layer coupling in this sliding multiferroic arises intrinsically from the spontaneous electrical and layer polarizations, eliminating the need for a sustained gate field to maintain the spin state. The two distinct multiferroic phases further exhibit a fully switchable anomalous Hall effect and a pronounced magneto-optical response, providing potential experimental signatures. These findings highlight the promise of leveraging sliding-mediated coupling between unconventional magnetism and stacking order to realize electrically programmable two-dimensional multiferroics.

Understanding lattice thermal transport in magnetic materials is crucial for their application in spintronic devices. However, the effects of dimensionality and magnetic order and disorder on phonon heat transport remain under debate. Here, we systematically investigate the lattice thermal conductivity ${\kappa }_{\ell }$ of monolayer, bilayer, and bulk ${\mathrm{CrI}}_3$ in both ferromagnetic (FM) and paramagnetic (PM) phases by developing an integrated computational framework that combines a type-differentiated moment tensor potential with the phonon Boltzmann transport equation. In this framework, spin-up and spin-down Cr atoms are explicitly distinguished, enabling the PM phase to be accurately described as a disordered local-moment state rather than as a nonmagnetic approximation. The results demonstrate that ${\kappa }_{\ell }$ in ${\mathrm{CrI}}_3$ exhibits a strong dimensional dependence. At 300 K, ${\kappa }_{\ell }$ decreases monotonically from monolayer to bulk in both FM and PM phases, with the reduction reaching as high as 53% and 55%, respectively. Such pronounced suppression is mainly caused by the weakening of low-frequency heat-carrying phonons, shortened phonon lifetimes, and reduced mean free paths. In contrast, the impact of magnetic disorder on thermal transport is found to be relatively weak, leading to only a 9%–14% reduction in ${\kappa }_{\ell }$. This weak dependence is consistent with the small differences in both harmonic and anharmonic interatomic force constants between the FM and PM phases, as well as the weak magnetic exchange interactions in ${\mathrm{CrI}}_3$. Our results provide a clear microscopic understanding of coupled spin-lattice thermal transport and establish an efficient computational framework. This framework enables reliable prediction of thermal transport properties in complex magnetic phases and holds promise for promoting the development of energy-efficient magnetic devices for information processing and storage.

Atomic ordering provides a route to modify local symmetry at fixed composition, but its influence on spin-orbit-coupled (SOC) responses remains difficult to separate from accompanying structural and electronic changes. Here, we use first-principles calculations to examine five Bi/Y occupation patterns in fixed-composition ${\left({\mathrm{Y}}_{0.5}{\mathrm{Bi}}_{0.5}\right)}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$. Reversing the site-order polarity leaves the equilibrium volume, band-gap scale, broadband manifold, and diagonal dielectric response nearly unchanged, while changing the distributions of Fe-centered projected density of states spectral centroids and the $\mathrm{Bi}\text{−}6p/\mathrm{Fe}\text{−}3d$ spectral weight near the conduction edge. The SOC-sensitive observables respond much more strongly: The effective [111]-projected magnetic anisotropy energy (MAE) density $K$ varies approximately linearly with the site-order parameter and changes sign near the occupation-balanced configuration, whereas the off-diagonal dielectric tensor and the resulting Kerr and Faraday spectra change markedly. These results establish site order as a fixed-composition control variable for reversing magnetic anisotropy and reshaping magneto-optical response without substantially altering the average structural or electronic framework.

The topological classification of a system depends on the discrete symmetries of its Hamiltonian. In Floquet photonic waveguide arrays, the abstract symmetries of the Altland-Zirnbauer (AZ) scheme—chiral, particle-hole, and time-reversal (for photonics, $z$-reversal)—arise from structural properties of the lattice, yet a systematic correspondence has not been established. Here, we illustrate this correspondence for a simpler system of one-dimensional waveguide arrays with real coupling coefficients, showing how bipartite structure and $z$-reflection symmetry alone determine the whole AZ class. We further demonstrate that nonbipartite networks—lacking conventional particle-hole symmetry, chiral symmetry, and $z$-reversal symmetry—can nonetheless support topologically protected boundary states at quasienergy $\varepsilon =\pi$, even in one dimension. The protecting symmetry—shifted-particle-hole symmetry—applies equally to higher-dimensional Floquet waveguides.

We develop a microscopic theory of superfluidity for hard-core dark excitons on the triangular lattice by mapping the large-$U$ Bose-Hubbard model to an effective XXZ spin-$\frac{1}{2}$ Hamiltonian including virtual hopping processes. Within this framework, we identify the superfluid phase that emerges between the two Mott-insulating endpoints at fillings 0 and 1, and derive its mean-field structure via a canted-spin solution. We then construct the corresponding continuum Landau-Ginzburg (LG) functional and analyze phase fluctuations and vortex dynamics. In two dimensions, the superfluid-normal transition is shown to be governed by a Berezinskii-Kosterlitz-Thouless (BKT) mechanism with a stiffness determined by microscopic parameters. Our results provide a unified description connecting lattice-scale exciton dynamics to continuum critical behavior in triangular geometries.

Electron-phonon ($e$-ph) interactions play a crucial role in determining many properties of materials. In this context, the Su-Schrieffer-Heeger (SSH) model, where atomic motion modulates the electronic hopping, has gained significant attention due to its potential for strong electron pairing in relation to high-$T_{\mathrm{c}}$ superconductivity. Previous studies of the SSH models have addressed many aspects of this problem, but have focused heavily on either dilute or half-filled models with dispersionless (Einstein) phonons. Here, we study the effects of dispersive optical phonons on the lightly doped one-dimensional optical Hubbard-SSH model using the density matrix renormalization group. We observe a significant enhancement in singlet binding driven by phonon dispersion; however, by calculating various correlation functions, we find that the enhanced binding does not translate to increased superconducting correlations but rather robust bond correlations in the studied parameter regime. Nevertheless, the significant impact of phonon dispersion on these correlations highlights the need to go beyond the Einstein phonon limit while modeling realistic quantum materials.

Recent advances in coherent conveyor-mode spin qubit shuttling are paving the way for large-scale quantum computing platforms with qubit connectivity achieved by spin qubit shuttles. We developed a simulation tool to investigate numerically the impact of device imperfections on the spin coherence of conveyor-mode shuttling in Si/SiGe. We simulate the quantum evolution of a mobile electron spin qubit under the influence of sparse and singly charged point defects placed in the Si/SiGe heterostructure in close proximity to the shuttle lane. We consider different locations of a single charge defect with respect to the center of the shuttle lane, multiple orbital states of the electron in the shuttle with $g$-factor differences between the orbital levels, and orbital relaxation induced by electron-phonon interaction. Our analysis isolates spin decoherence arising from orbital excitations induced by charged defects in close proximity of the shuttled electron. With this simulation framework, we quantify the impact of individual charged defects on qubit coherence and determine the range of defect densities compatible with high-fidelity conveyor-mode spin shuttling.

Electrical control of valley polarization in two-dimensional systems has been intensively studied, yet existing approaches are largely limited to tuning its magnitude within a given band, without access to the distinct carrier and spin characteristics associated with different bands. Here, based on first-principles calculations, we demonstrate that ferroelectric polarization can be utilized to control magnetic proximity effects and realize band-selective valley polarization in two-dimensional heterostructures. Using monolayer $1T^{″}\text{−}{\mathrm{MoSe}}_2$ interfaced with ferromagnetic ${\mathrm{CrI}}_3$ as a model system, we show that polarization reversal redistributes the band-edge wave functions along the out-of-plane direction, thereby selectively modulating their coupling to the magnetic substrate. This leads to band-dependent proximity-induced exchange splitting, which is switched from the valence band to the conduction band. Since these bands correspond to different carrier types and opposite spin polarization, the polarization reversal enables switching not only the band hosting the valley-polarized carriers but also the associated valley Hall and spin Hall effects. Our results demonstrate an electrically controllable way to manipulate magnetic proximity effects and establish a mechanism for reconfigurable spin-valley transport in two-dimensional systems.

Conventional planar waveguides confine light to linearly polarized TE and TM modes, inherently limiting optical spin control. Here, we demonstrate the generation of transverse optical spin textures via TE-TM mode hybridization in a deformed uniaxial dielectric slab. We show that monoclinic deformation—which shares the same symmetry properties as the Rashba Hamiltonian—induces a Rashba-like dispersion splitting, characterized by out-of-plane transverse spin. Conversely, a gyrotropic deformation—which shares the same symmetry properties as the Zeeman Hamiltonian—produces a concentric Zeeman-like splitting, where spin orientation is independent of propagation direction. Using a Hamiltonian reformulation of Maxwell's equations and symmetry analysis, we derive the precise TE-TM anticrossing conditions and fully characterize these emergent spin textures, establishing a robust platform for integrated spin photonics.

We investigate the ground-state properties of spinless fermions on a two-leg ladder by allowing the nearest-neighbor hopping dimerization in one leg and uniform hopping in the other. In the noninteracting limit, we find that at half filling, the system exhibits robust topological behavior if the interleg hopping is allowed. Though depending on the dimerization pattern, the dimerized leg can be either topological or trivial in nature; here we show that by connecting such a leg to a uniform leg through interchain coupling, the overall system becomes topological irrespective of the dimerization pattern in the dimerized leg. As a result, a topological phase transition occurs as a function of the interleg hopping. When the interleg interaction is turned on, the topological phase survives and we obtain an interaction-induced topological phase transition. Finally, we reveal that when uniform interactions are included on all the bonds of the ladder, the topological phase transitions to a symmetry-broken charge-density wave (CDW) phase.

The simulation of strongly correlated electron systems remains a formidable challenge. Certain experimentally relevant dynamical response functions are especially difficult to calculate, because of issues of finite-size effects and the ill-posed analytic continuation. To address this, we propose the quantum cluster embedding theory, an embedded cluster method aimed at computing the response of the system following an external perturbation; the frequency-dependent dynamical susceptibility is obtained subsequently by means of inverse linear response theory. The embedded clusters, used within the method as representatives of short-range correlations, are open quantum systems governed by the Lindblad equation. The short-range correlations extracted from the clusters are used to close the equations of motion for the fermionic bilinear and the local double occupancy on the lattice. In turn, the clusters' Markovian baths are tuned to keep the bilinear and the double occupancy expectation values on the clusters and the lattice identical, throughout the concomitant evolution of the two sets of equations. The theory becomes numerically exact in the noninteracting, atomic, and infinite-cluster-size limits, and it respects the total charge and energy conservation laws. We show that our approach can treat very large lattices while avoiding analytic continuation through the explicit time evolution. Finally, we compute the charge-charge correlation function in the square lattice Hubbard model and compare with a recent cold atom experiment, finding good qualitative agreement.

Strong lattice anharmonicity fundamentally alters phonon dynamics and challenges the conventional phonon quasiparticle description of thermal transport. Using ${\mathrm{Sn}}_2{\mathrm{S}}_3$ as a representative strongly anharmonic crystal, we investigate the role of temperature-induced phonon renormalization on lattice thermal conductivity by combining the temperature-dependent effective potential method with the Wigner transport equation, which explicitly captures both particlelike and coherent phonon transport channels. We show that theoretical descriptions based on unrenormalized zero-temperature interatomic force constants systematically underestimate the lattice thermal conductivity, while one-shot finite-temperature fitting approaches significantly overestimate it. By explicitly accounting for temperature-dependent renormalization of both harmonic and anharmonic interactions, we achieve quantitative agreement with experimental measurements over a wide temperature range. Our analysis reveals that although phonon dispersions exhibit only moderate temperature-induced changes, phonon lifetimes are substantially enhanced due to a pronounced reduction in effective cubic anharmonicity. This enhancement activates significant heat-carrying contributions from low- and intermediate-frequency optical phonons, strengthening the particlelike transport channel. In contrast, the coherent contribution to thermal transport is suppressed with thermal renormalization. These results establish temperature-induced anharmonic renormalization as a key mechanism governing thermal transport in ${\mathrm{Sn}}_2{\mathrm{S}}_3$ and provide an alternative perspective for understanding heat conduction in strongly anharmonic crystalline solids.