The germanium vacancy in diamond (GeV) is a promising candidate for color center based quantum networking. Yet, like for other group-IV vacancy defects in diamond, achieving fast, high-fidelity qubit operations using traditional magnetic resonance techniques is experimentally challenging due to a weak magnetic dipole and susceptibility to thermally induced decoherence. Here, we perform all-optical control of the GeV and realize Rabi frequencies exceeding $\sim 20$ MHz. We do so by driving the two $\mathrm{\Lambda }$-systems of the GeV simultaneously and apply this to probe the spin coherence ($T_2^{*}=224\pm 14$ ns, $T_2^{\mathrm{H}}=11.9\pm 0.3 \mu \text{s}$). Our control scheme is applicable to other color centers and particularly, other group-IV defects for which the scheme may be optimized to improve all-optical control in these systems.

Motivated by transition-metal trihalides, we study the strong-coupling model of $d^1$ honeycomb lattice systems in the large spin-orbit coupled limit. By considering different possible hopping pathways, SU(4) symmetry is found to emerge at multiple points in the parameter space of the hopping parameters. The resultant Dirac spin-orbital liquids, within the parton mean-field description, provide distinct realizations of symmetry fractionalization. The calculated dynamical spin-structure factor fingerprints this distinctive nature, measurable in experiments. The conclusions are found to be perturbatively robust upon inclusion of low-energy gauge fluctuations.

The acoustic coupled-cavity system offers a versatile platform for exploring novel topological phenomena such as topological pumping and beyond, wherein long-range coupling, as an emerging modulation strategy, is typically introduced via extrinsic connection elements or moving fluids, resulting in increased systemic complexity or unwanted fluid-induced noise. Here, we exploit intrinsic next-nearest-neighbor (NNN) couplings within coupled-cavity systems as a controllable degree of freedom and, based on it, demonstrate a remarkable effect of asymmetric topological pumping in a compact spatially modulated acoustic lattice without extra coupling tubes and moving fluids. Through a higher-order approximation, we theoretically reveal and experimentally demonstrate that the intrinsic long-range coupling, which is commonly overlooked in previous designs, can be significantly amplified and independently modulated via rationally designing the structural parameters. As the NNN coupling increases, asymmetric band compression leads to highly uneven spectral spacings, ultimately triggering the directional breakdown of pump channels. Simulation results confirm the asymmetric pumping of sound in the spatially modulated lattices irrespective of whether nonparaxial or paraxial conditions are applied. Our findings may advance the exploration of topological phases enriched by NNN coupling and provide a design paradigm for compact acoustic devices enabling direction-selective wave control.

We propose to incorporate grain boundary (GB) anisotropy in phase-field modeling by extending the standard partial differential equations (PDEs) formulation to include a nonlocal functional of an orientation field. Regardless of the number of grains in the simulation, the model uses a single orientation field and incorporates grain misorientation and inclination information obtained from sampling the orientation field at optimized locations in the vicinity of the GB. The formalism enables simple and precise tuning of GB energy anisotropy while avoiding an extensive fitting procedure. The functional includes explicit GB functions to control the GB energy as a function of both misorientation and inclination. The model is validated by reproducing the linear grain growth rate, Wulff shapes with varying misorientations and anisotropic coefficients, and analytical equilibrium dihedral angles at triple junctions. Polycrystalline simulations further demonstrate grain growth, coalescence, triple junction behavior, and the influence of anisotropy on grain morphology.

The martensitic transition temperature (MTT) of a shape-memory alloy (SMA) is one of its most important characteristics, determining its operating temperature, while the energy difference ($\mathrm{\Delta }E$) between the austenite and martensite phases is among the most crucial factors dictating MTT. Using density-functional theory, $\mathrm{\Delta }E$ of NiTi, the most studied and commonly used SMA, varies from 23 to 116 meV/atom, depending on the density functional [Wu and Lawson, J. Chem. Phys. 161, 134104 (2024)]. Consequently, free-energy calculations using different density functionals yield MTTs that differ by several hundred K. Here, we benchmark $\mathrm{\Delta }E$ of NiTi using diffusion quantum Monte Carlo. With this method, the energy difference is estimated to be $70.9\pm 2.5$ meV/atom.

Detailing emergent quantum phenomena predicted for hydrogen at high densities remains a key challenge in condensed matter physics. A first-order issue is stabilization of the quantum fluid relative to solid phases at multimegabar $(>100\mathrm{GPa})$ pressures, a problem for which accurate large-scale simulations can play a critical role in predicting behavior beyond the range of current pressure-temperature $\left(P\text{−}T\right)$ experiments. Here, we developed a machine-learned interatomic potential for hydrogen trained on accurate diffusion quantum Monte Carlo data, including total energies and atomic forces, which allows us to investigate the melting curve of hydrogen over a broad range of pressures. Our simulations predict a broad melting maximum near 1000 K at $100–150\mathrm{GPa}$, followed by a leveling off in the melting temperature at higher pressure, in good agreement with experiment. Beyond the range of current experiments, the simulations predict that hydrogen melts near room temperature and is remarkably independent of pressure from 500 to 900 GPa. Our results suggest that hydrogen does not have a fluid ground state up to terapascal pressure and provide a baseline for understanding this exotic quantum material at ultrahigh pressures.

The nonintegrable transverse-field Ising model is a common platform for studying ergodic quantum dynamics. In this work, we introduce a simple variant of the model in which this ergodic behavior is suppressed in the finite-size regime by introducing a spatial inhomogeneity in the interaction strengths. For this we partition the chain into two equal segments within which the spins interact with different coupling strengths. The ratio of these couplings defines an inhomogeneity parameter, whose variation away from unity leads to the mentioned constrained dynamics. We characterize this crossover using multiple diagnostics, such as the long-time saturation of out-of-time-ordered correlators, level-spacing statistics, and the spectral form factor. Making use of this tunable ergodic behavior, we can examine the impact of dynamical features towards operator spreading in the Krylov space and also for entanglement generation in the system's eigenstates. Unlike the monotonic behavior of the aforementioned diagnostics, the saturation of Krylov complexity shows a nontrivial suppression near the onset of constrained dynamics, which can be explained by quantifying the spread of the initial operator in the Krylov space. Together, these results demonstrate that introducing a macroscopic inhomogeneity in coupling strengths provides a minimal, disorder-free route to constraining the ergodic nature in this specific model of interacting spins, particularly in the finite-size regime. These effects are prominently reflected in a Krylov space analysis.

Disordered nonlinear systems have long been central to studies of complex dynamical behavior, yet most studies focus on spatial randomness. In contrast, when disorder fluctuates temporally, it drives the system far from equilibrium, giving rise to fundamentally different dynamical behaviors. Here, we investigate a nonlinear dispersive system subject to correlated temporal disorder, revealing how the interplay between dispersion and temporal disorder reshapes its dynamical phases. By analyzing correlation dynamics and replica-overlap statistics, we identify a transition from ergodic to nonergodic clustering, marked by distinct correlation patterns and symmetry breaking in replica statistics. These results clarify the statistical mechanics underlying temporally disordered nonlinear waves and provide insight into nonequilibrium phase organization in time-varying photonic systems.

We investigate dynamical quantum phase transitions (DQPTs) in generic Dirac Hamiltonians following a sudden quench. By deriving an exact analytical expression for the Loschmidt amplitude (LA), we establish a universal criterion for DQPTs in this broad class of systems. We introduce first- and second-order dynamical topological order parameters (DTOPs) to characterize DQPTs. Geometrically, the second-order DTOPs track the evolution of (d-2)-dimensional topological defects on a special (d-1)-dimensional surface dictated by the universal criterion. In the short-time regime, we uncover a direct link between three distinct phenomena: the reconfiguration of topological defects, the emergence of van Hove singularities in the density of LA zeros, and non-analyticities in the rate function. In the long-time limit, the defects coalesce into a dense domain-wall structure on the (d-1)-dimensional surface. We show that this critical surface is inherent to both the time-averaged pseudospin polarization and the Hamiltonian. Our general framework is validated through its application to a three-dimensional four-band Dirac model. These results provide a theoretical foundation for studying DQPTs in topological systems, particularly in higher dimensions. The developed methodology is directly extendable to other quench protocols and to non-Hermitian generalizations of Dirac Hamiltonians.

The interpretation of high harmonic generation (HHG) in solids typically relies on phenomenological dephasing times far shorter than what is expected from microscopic scattering processes. Here we show that zero-point fluctuations associated with optical phonons naturally suppress long-range electronic coherences and generate clean harmonic spectra without introducing ad hoc decoherence parameters. Using a one-dimensional semiconductor composed of two distinct sites per unit cell and realistic phonon amplitudes, we demonstrate that random per-site optical-phonon jitter reproduces the spectral sharpening typically attributed to ultrafast $T_2$ dephasing. In contrast, acoustic phonons and local strain, whose distortions are correlated over nanometer scales, produce negligible spectral cleaning. We further show that such long-range site coherence leads to carrier-envelope-phase (CEP)-dependent effects in the HHG spectrum driven by long pulses, but these effects are lost once optical-phonon-induced decoherence is included. Our results (i) identify optical zero-point motion as a key mechanism governing coherence in solid-state HHG, (ii) demonstrate that it can be qualitatively modeled in periodic solids through site-distance-dependent dephasing, and (iii) suggest that CEP-resolved measurements can probe electronic coherence lengths and atomic fluctuations in crystalline materials.

Host-guest crystalline materials with strong anharmonicity exhibiting long-range order and local disorder offer a paradigm for ideal thermoelectric model known as the “phonon-glass electron-crystal” (PGEC), which ensures efficient electrical conduction characteristic of crystals while suppressing thermal transport in a glasslike manner. It is widely accepted that guest atoms introduce low-frequency low-lying optical phonons (referred to as rattling modes), which intensely scatter the acoustic phonons, thereby drastically reducing lattice thermal conductivity (${\kappa }_L$). In quasi-one-dimensional (Q-1D) thermoelectrics, this mechanism is conceptualized as covalent 1D chains forming the host framework, with isolated interchain ions acting as charge-balancing rattlers to further dampen ${\kappa }_L$. However, our first-principles studies of the Q-1D perovskite $\delta \text{−}\mathrm{CsSn}{\mathrm{I}}_3$ reveal that the covalent 1D chains serving as host frames also produce low-lying optical phonons, which introduce additional three-phonon scattering channels. Utilizing self-consistent phonon theory and Wigner transport formalism, we capture phonon frequency renormalization and wavelike coherent scattering. This approach uncovers an ultralow ${\kappa }_L$ with weak temperature dependence, consistent with the results from homogeneous nonequilibrium molecular dynamics. Furthermore, based on a low-order expansion of electron-phonon coupling, we estimate a thermoelectric figure of merit $\mathit{ZT}$ up to 0.53 (0.92) at 300 (425) K for $\delta \text{−}\mathrm{CsSn}{\mathrm{I}}_3$. Notably, we identify the low-lying optical branches originating from the antiparallel sliding of the host 1D chains, offering additional phonon scattering channels for damping phonon transport. These findings offer new microscopic insights into Q-1D thermoelectric transport and provide a viable material platform and a design scheme to explore PGEC behavior in anisotropic systems.

We investigate a quasiperiodically driven four-level system that serves as a temporal analog of topological phenomena found in four-band models with intertwined spin and orbital degrees of freedom. Under a two-tone drive in the strong-driving regime, the system realizes a two-dimensional synthetic Floquet lattice, thus facilitating the realization of topological energy pumping. For a temporal quantum spin Hall insulator, we find that the rates of emission and absorption of energy between the two drives are not exactly opposite for a given band. However, when contributions from two chiral symmetric partner bands are added, they become exactly opposite. This quantized rate of energy exchange is a direct consequence of propagating edge modes in the real-space model, which we further characterize by computing the spin-Chern number. Interestingly, our analysis yields a zero rate of exchange of energy between the drives for a temporally higher-order topological insulator, suggesting the presence of localized corner modes that we characterize by the mid-gap Wannier spectra. Our findings uncover the role of chiral, particle-hole, and time reversal symmetries on the energy dynamics in temporal quantum spin Hall and higher-order topological insulators. Finally, we demonstrate that the perfect (imperfect) nature of the fidelity during the time evolution of the system serves as a characteristic signature of a topological (trivial) phase.

Understanding and optimizing the relaxation dynamics of many-body systems is essential both for foundational studies in quantum thermodynamics and for applications such as quantum simulation and quantum computing. Efficient preparation of thermal states of a many-body Hamiltonian is governed by the spectral properties of the associated Lindbladian, in particular its spectral gap, which determines the minimum relaxation rate. In this work, we develop a systematic framework for constructing Lindbladians that prepare thermal states. Our approach reveals a simple relation between the relaxation dynamics at finite and infinite temperatures. The framework is scalable to larger system sizes when implemented using tensor-network methods. We find that efficient thermalization requires that the relaxation dynamics respect the symmetries of the thermal state, which reduces the number of free parameters. By applying gradient-based optimization to the Lindbladians, we enhance the spectral gap and thereby boost thermalization. When applied to both classical and quantum spin models, our method demonstrates a substantial enhancement of the spectral gap. For larger system sizes, our approach provides a variational upper bound and enables a certified lower bound on the spectral gap.

The significance of anomalous Hall effect (AHE) lies in its capability of the interconversion between spin and charge information. The van der Waals (vdW) ferromagnet $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$ has attracted extensive interest owing to its high Curie temperature and strong perpendicular magnetic anisotropy. Here, we report a comprehensive Tian-Ye-Jin (TYJ) scaling analysis combined with density functional theory (DFT) calculations to elucidate the origin of the AHE in $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$. We have separated the contributions to the AHE from three distinct mechanisms: skew scattering, side-jump, and intrinsic Berry curvature. Our DFT calculations reveal that the intrinsic contribution is attributed to the transitions between Fe-$d_{xz/yz}$ and Te-$p_{x/y}$ orbitals. Furthermore, we find that electron-magnon scattering significantly influences electrical transport, giving rise to a quadratic dependence between magnetoresistance variation and side-jump scattering. Our findings advance the understanding of AHE and electron-magnon scattering in vdW magnets and would facilitate applications of $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$ in spintronic devices.

Altermagnets with spin-layer coupling (SLC) enable symmetry-protected spin splitting without net magnetization. In the SLC altermagnet $\mathrm{Ca}{\left(\mathrm{CoN}\right)}_2$ monolayer, which exhibits distinct sublayer-dependent spin and valley characteristics, we demonstrate that breaking the sublayer-exchange symmetry S via ferromagnetic substrates $({\mathrm{CoCl}}_2 \text{and} \mathrm{CoSe})$ induces robust, magnetization-tunable spin-valley splitting, with the magnitude mainly depending on the strength of interfacial interactions. First-principles calculations reveal that strong interfacial charge redistribution and exchange coupling generate spin-valley splitting for both the valence band maximum (VBM) and conduction band minimum (CBM) of $\mathrm{Ca}{\left(\mathrm{CoN}\right)}_2$. In $\mathrm{Ca}{\left(\mathrm{CoN}\right)}_2/{\mathrm{CoCl}}_2$, antiferromagnetic interfacial exchange produces large spin-valley splitting for CBM but only minor splitting for VBM, with $\mathrm{\Delta }{E}_{\mathrm{V}}=$ −0.016 and 0.019 eV corresponding to upward and downward magnetic orientations of ${\mathrm{CoCl}}_2$, respectively. In contrast, CoSe exhibits ferromagnetic interfacial exchange and pronounced interfacial charge redistribution, forming prominent Co-Se bonding and antibonding states near the Fermi level under opposite substrate magnetic orientations, resulting in larger spin-valley splitting $(\mathrm{\Delta }{E}_{\mathrm{V}}=0.075 \text{and} -0.604 \mathrm{eV})$ consistent with sublayer-resolved band shifts. Device-level spin-transport simulations of the van der Waals (vdW) tunneling junctions further confirm a magnetization-controlled, spin-valley-dependent transport, with $k$-resolved maps revealing anisotropy in transmission coefficients. These results demonstrate that vdW heterostructure engineering provides a promising route for achieving large and magnetization-tunable spin-valley splitting in spintronic and valleytronic devices based on altermagnetic materials.

Magnetic skyrmions extended to three dimensions form stringlike objects whose fundamental role remains largely unexplored. We show that skyrmion strings can terminate on a Néel-type domain wall (DW), realizing a magnetic analog of a Dirichlet(D)-brane soliton. While an isolated Néel DW tends to rotate into a Bloch DW, the Néel DW is stabilized when a skyrmion string ends on it, by being transformed into a trumpet. Unlike field-theory D-branes, the Bloch-type DMI produces linear rather than logarithmic DW bending, and the strings retain finite width far from the DW, circumventing singular behavior. Furthermore, the repulsive interaction between strings allows periodic multijunction solutions, yielding a square lattice of alternating strings and local DW deformations as well as separating Bloch points. These results establish magnetic skyrmion strings as fundamental strings that can end on a D-brane.

We report calorimetric, magnetic, and neutron scattering studies on an $S=5/2$, nearly Heisenberg triangular-lattice antiferromagnet ${\mathrm{K}}_2\mathrm{Mn}{\left({\mathrm{SeO}}_3\right)}_2$ with weak XXZ easy-axis anisotropy. Multiple magnetic phases are identified, including a noncollinear Y phase in zero field, a field-induced collinear $m=1/3$ magnetization plateau, and a high-field V phase. In the Y phase, the magnetic excitation spectrum exhibits both single-magnon excitations and an extended high-energy continuum. Both features are well described by nonlinear spin wave theory. In the field-induced phases, complex effects of the spectrum renormalization even for large $S=5/2$ material are clearly detectable. These results underscore the essential role of magnon-magnon interactions in the dynamics of large-$S$ Heisenberg spin systems on a triangular lattice.

We systematically investigate $g$-factor anisotropy in two-dimensional van der Waals magnets $\mathrm{Cr}{X}_3$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$ using broadband magnetic resonance for magnetic ordered states below the critical temperature $\left(T_{\text{cr}}\right)$ and for paramagnetic states above $T_{\text{cr}}$, with varied field orientations. Despite sharing the same layered honeycomb lattice, these compounds exhibit contrasting anisotropies: ${\mathrm{CrCl}}_3$ is an easy-plane antiferromagnet, whereas ${\mathrm{CrBr}}_3$ and ${\mathrm{CrI}}_3$ are easy-axis ferromagnets. From temperature-dependent resonance dispersions with fields applied parallel and perpendicular to the $\mathit{c}$ axis, we uncover opposite trends of $g$-factor anisotropy: $g_{\mathrm{c}}>g_{\mathrm{ab}}$ in ${\mathrm{CrBr}}_3$ and ${\mathrm{CrI}}_3$, but $g_{\mathrm{c}}<g_{\mathrm{ab}}$ in ${\mathrm{CrCl}}_3$. Across the $\mathrm{Cr}{X}_3$ family, both the sign and the magnitude of the $g$ shift are found to correlate closely with the effective anisotropy field, suggesting that magnetic anisotropy provides a useful handle for tuning spin dynamics in van der Waals magnets.

Symmetry constraints determine which physical responses are allowed in a given system. Magnetization induced by strain fields—such as in piezomagnetic and flexomagnetic effects—has typically been studied in materials that break time-reversal symmetry. Here, we propose that nonuniform strain can induce magnetization even in nonmagnetic metals and semiconductors that preserve time-reversal symmetry. This mechanism differs from the conventional flexomagnetic effect: the strain gradient acts as a driving force on the electrons, generating magnetization in a manner closely analogous to current-induced magnetization. Treating the strain field as an external field, we derive a general expression for the magnetization induced by a strain gradient and demonstrate that this response is symmetry-allowed even in time-reversal symmetric systems. We apply our formulation to nonmagnetic systems that lack spatial inversion symmetry while preserving time-reversal symmetry, using a decorated square lattice, monolayer ${\mathrm{MoS}}_2$, and monolayer Janus MoSSe as representative examples. We find a finite magnetization response to strain gradients which is consistent with symmetry arguments, supporting the validity of our theoretical framework. These results offer a pathway for controlling magnetization in nonmagnetic materials using strain fields.