Understanding the microscopic mechanisms of energy exchange between lattice and spin degrees of freedom is fundamental to the development of next-generation spintronic and magnonic devices. Here we employ transient absorption (TA) spectroscopy to investigate the nonequilibrium spin dynamics in antiferromagnetic cobalt oxide films following photoexcitation. We demonstrate that the TA features associated with the $d\text{−}d$ transitions of transition metal ions act as an effective thermometer for tracking transient spin temperature. Below the Néel temperature, we observe a slow, nanosecond-scale rise in spin temperature, which we attribute to energy transfer from the photoheated lattice to the spin subsystem. Our analysis reveals that the spin-lattice coupling coefficient follows a $T^3$ power-law dependence, consistent with a microscopic model where the energy transfer rate is governed by the thermal occupancy of magnons in the presence of a large hot phonon population. These findings establish $d\text{−}d$ transitions as a sensitive spectroscopic probe for nonthermal spin dynamics and provide fundamental insights into the scaling laws governing spin-lattice equilibration in antiferromagnetic oxides

Magnetic pyrochlore oxides exhibit various unconventional electronic phases and excitations due to geometric frustration. Recently, a collective magnetic excitation was reported in Raman spectroscopy on a pyrochlore ruthenate ${\mathrm{Nd}}_2{\mathrm{Ru}}_2{\mathrm{O}}_7$. However, its origin remains unclear as the Ru magnetic ground state has been controversial due to sample quality and inconsistent experimental interpretations. Here, we performed neutron diffraction measurements on a high-quality polycrystalline sample with a nearly absent magnetic impurity phase. Magnetic susceptibility and neutron diffraction measurements reveal an intrinsic Ru magnetic transition at around 145.6 K, whereas a controversial magnetic anomaly at around 21 K is suppressed in our sample, indicating that the latter is dominantly from the magnetic impurity phase. Below 145.6 K, well-defined magnetic Bragg peaks from Ru moments were observed, implying well-formed spin-spin correlations. Magnetic refinements combined with magnetic space group analysis revealed competing Ru magnetic structures, supported by density functional theory calculations. Our results suggest that the collective Raman signal may arise from competing Ru magnetic orders. Order-by-disorder and energetic scenarios are discussed as selection mechanisms for the Ru magnetic ground state. This study provides crucial insights into the search for possible order-by-disorder and topological magnetic properties in a less-studied spin-1 pyrochlore.

Ultrafast spin dynamics in ferrimagnets underpin high-speed spintronic devices that combine rapid magnetic dynamics with finite magnetization for electrical detection. Here we investigate the ultrafast magnetization and lattice dynamics in ferrimagnetic antiperovskite ${\mathrm{Mn}}_4\mathrm{N}$ epitaxial thin films on ${\mathrm{SrTiO}}_3$ using time-resolved magneto-optical Kerr spectroscopy. Structural characterization reveals a tetragonal distortion induced by epitaxial tensile strain, which stabilizes strong perpendicular magnetic anisotropy. Following femtosecond optical excitation, the magnetization exhibits an ultrafast demagnetization with a characteristic time of $\sim 190\mathrm{fs}$, followed by two recovery components with different timescales, which suggest temporally distinct responses of the inequivalent Mn sublattices. Field-independent demagnetization dynamics indicate that the process is governed primarily by intrinsic electronic scattering rather than external magnetic perturbations. We further demonstrate gigahertz spin precession frequencies and remarkably low Gilbert damping ($\sim 0.02$). In addition, coherent acoustic phonon modes in the tens-to-hundreds of GHz range are detected, revealing temperature-dependent lattice softening. These results provide insight into the coupled spin-lattice dynamics of rare-earth-free ferrimagnetic nitrides and highlight ${\mathrm{Mn}}_4\mathrm{N}$ as a promising platform for ultrafast spintronic applications.

We demonstrate that the infinite-$U$ triangular-lattice Hubbard model supports a superconducting state built from tightly bound Cooper pairs composed of two holes and one magnon ($2h1m$). Building on the seminal prediction of repulsively bound $2h1m$ states, we show that next-nearest-neighbor hopping $t_2$ coherently mixes symmetry-related configurations, stabilizing an $s$-wave bound state with substantial binding energy and a light effective mass. Large-scale density matrix renormalization group calculations at finite doping reveal, over a finite magnetic-field window, a magnetization plateau with one magnon per pair of doped holes and quasi-long-range superconducting order characterized by algebraically decaying $2h1m$ correlations. Our results establish a kinetically driven superconducting phase of composite magnonic Cooper pairs and provide directly measurable signatures for moiré Hubbard materials and ultracold-atom simulators.

We develop a variational method for interacting surface systems with higher-form global symmetries. As a natural extension of the conventional second-quantized Hamiltonian of interacting bosons, we explicitly construct a second-quantized Hamiltonian formulated in terms of a closed surface operator $\widehat{\varphi }\left[C_p^{}\right]$ charged under a $p$-form global symmetry. Applying the variational principle, we derive a functional Schrödinger equation analogous to the Gross–Pitaevskii equation in conventional bosonic systems. In the absence of external forces, the variational equation admits a uniform solution that is uniquely determined by a microscopic interaction potential $U\left({\psi }^{*}\psi \right)$ and the chemical potential. This uniform solution describes a uniform gas of bosonic surfaces. Using the obtained energy functional, we show that low-energy fluctuations contain a gapless $p$-form field $A_p^{}$ when the $p$-form global symmetry is $\mathrm{U}\left(1\right)$, whereas the $p$-form field becomes massive for discrete symmetries, whose low-energy limit is described by a BF-type topological field theory. As a consequence, the system exhibits Abelian topological order with anyonic surface excitations. In the presence of external forces, however, solving the functional equation in full generality remains challenging. We argue, however, that the problem reduces to solving the conventional Gross–Pitaevskii equation when external forces act separately on the center-of-mass and relative motions. In addition, we present analytic solutions for topological defects as analogs of vortex and domain-wall solutions in conventional bosonic systems. Finally, as a concrete microscopic model, we study a ${\mathbb{Z}}_N^{}$ lattice gauge theory and show that our variational method correctly reproduces the ground states in the analytically solvable limits.

${\mathrm{K}}_2{\mathrm{Ni}}_2{\left({\mathrm{SO}}_4\right)}_3$ is a member of the langbeinite family, consisting of two intertwined $S=1$ trillium lattices, of which one is strongly coupled (strong-TL) and the other is weakly coupled (weak-TL). Further intertrillium interactions give rise to a highly frustrated Heisenberg Hamiltonian. Despite ordering at low temperatures, ${\mathrm{K}}_2{\mathrm{Ni}}_2{\left({\mathrm{SO}}_4\right)}_3$ lies close in parameter space to a spin-liquid region that surrounds the tetratrillium limit, where each triangle belonging to the strong-TL turns into a tetrahedron by connecting to a single spin from the weak-TL. Here, we compare the experimentally determined magnetization process using pulsed magnetic fields up to 40 T with classical Monte Carlo calculations, uncovering a series of phase transitions at both low and intermediate fields. Furthermore, we reveal a signature of a $2/3$ magnetization plateau consisting of a $1/3$ phase on the strong-TL and a fully polarized phase on the weak-TL. Although in the classical limit no plateau is expected, we find a very prominent dome structure reflecting the tendency of the system to stabilize this particular spin configuration. The presence of a dome leads to a reentrant phenomenon in which the system recovers the Hamiltonian symmetries when increasing the magnetic field. Finally, we show that this plateau-like phase is also present in the classical Heisenberg model on the single trillium and tetratrillium lattices, indicating its possible presence in the large family of double-trillium langbeinite compounds. Our findings motivate future studies on the presence of the plateau phase in the quantum limit of both trillium and double-trillium materials within the langbeinite family.

The effective mass approximation is widely used across models of carrier transport, optical response, and excitons in semiconductors and insulators, but its validity hinges on the assumption that the band dispersion $E_n\left(\mathbf{k}\right)$ at the relevant extremum is analytic. We prove that analyticity holds at any nondegenerate extremum for Kohn-Sham density functional theory (DFT) with local or hybrid exchange-correlation functionals, for Hartree-Fock, and for band-edge $G_0{W}_0$ quasiparticle energies in gapped systems. Band nonanalyticity (or warping) in these settings is therefore intrinsically tied to degeneracy. We then use group theory to determine the symmetry-allowed form of the effective mass tensor for each of the 32 crystallographic point groups, providing a stringent consistency check on first-principles calculations. As a representative application, we show that the electron and hole effective masses at the $K$ point of monolayer ${\mathrm{MoS}}_2$ must be strictly isotropic at the DFT and $G_0{W}_0$ levels.

Understanding how electronic transport evolves from localized to itinerant regimes in correlated cluster solids remains an important challenge in condensed-matter physics. Here, we investigate the pressure-dependent transport properties of the lacunar spinel ${\mathrm{GaNb}}_4{\mathrm{Se}}_8$, a cluster Mott insulator at ambient conditions. At ambient pressure, the resistivity follows Efros-Shklovskii variable-range hopping, indicating Coulomb gap–controlled carrier localization. A pressure-induced electronic delocalization process begins at low pressures (∼5 GPa), as evidenced by the continuous suppression of room-temperature resistance. Upon further compression, the system undergoes a broad insulator-to-metal-like crossover in low-temperature transport, culminating in a fully metallic-like ground state at ∼17–18 GPa. In contrast, the crystallographic transition from the cubic phase to the monoclinic $C2$ phase starts at ∼20 GPa and ends near ∼32 GPa, demonstrating that the pressure-induced electronic evolution is completed before the onset of long-range structural symmetry breaking. At higher pressures, superconductivity (with a superconducting coherence length ξ(0) ≈ 80–90 Å) emerges from a pressure-induced metallic-like regime. These results establish ${\mathrm{GaNb}}_4{\mathrm{Se}}_8$ as a platform for studying correlation-driven evolution of electronic transport in cluster-based solids.

We report a machine-learned interatomic potential for uranium dioxide with xenon gas, as well as a machine-learned potential for uranium dioxide. Training datasets were constructed by leveraging a combination of density functional theory calculations with a Hubbard $U$ correction and molecular dynamics simulations. Query-by-committee active learning procedures further automated the augmentation of training datasets. The efficacy of employing an equivariant message-passing neural network for iterative potential fitting was demonstrated by reproducing $\mathrm{DFT}+U$-level forces and energies, despite the training datasets being much smaller than those for recently reported uranium dioxide MLPs. We found that our machine-learned potential for ${\mathrm{UO}}_2$ achieves strong agreement with experimentally observed thermophysical and thermomechanical properties across a temperature range 300–3000 K. Our second machine-learned potential for uranium dioxide with xenon successfully replicates reference $\mathrm{DFT}+U$ incorporation energies of xenon into various lattice sites. We also employed this MLP to calculate migration barriers for xenon diffusion via tetravacancy defect cluster mechanisms. The superlative ability of these machine-learned potentials to capture the behavior of uranium dioxide with xenon inclusion across a range of temperatures and defect chemistries lays the foundation for larger-scale molecular dynamics simulations of fission gas transport through uranium oxide fuel matrices.

The Hatsugai-Kohmoto (HK) model is an exactly solvable electronic lattice model where the interaction between electrons with opposite spin is diagonal in momentum space. We generalize the HK model by introducing momentum-mixing Landau interactions. Within a self-consistent mean-field analysis we find that the ground state of this model exhibits a partially flat energy band, in agreement with the fermion condensation scenario proposed by Khodel and Shaginyan [JETP Lett. 51, 553 (1990)]. Inspired by Anderson's pseudospin formulation of Bardeen-Cooper-Schrieffer theory, we show that the HK model with Landau interactions can be mapped onto a generalized Ising model where each site of the reciprocal lattice hosts two Ising spins. In the pseudospin picture the emergence of a partially flat electronic band corresponds to the smoothing of a magnetic domain wall. Moreover, guided by the pseudospin picture, we propose an exactly solvable variant of the HK model which has a unique ground state for all densities.

Image-potential surface states are simple model systems, where spin-dependent effects can be studied in view of spintronic applications. The Rashba effect in surface states at high-$Z$ materials is related to both the strong spin-orbit interaction in heavy atoms and the orbital angular momentum arising from the inversion-symmetry breaking at the surface. Our study on image-potential states at ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ showcases that the orbital angular momentum causes an intrinsically reversed Rashba parameter ${\alpha }_{\mathrm{R}}\approx -100\mathrm{meV}\AA$, i.e., a reversed spin splitting compared with the prototypical Rashba-split Au(111) crystal-induced surface state. We present a consistent picture of spin-resolved experimental data from inverse photoemission and three-photon photoemission together with calculations from density-functional theory and many-body perturbation theory.

The coexistence of out-of-plane and in-plane electric polarization is rare in two-dimensional (2D) ferroelectric materials, yet the two configurations offer distinct advantages for ferroelectric-based devices. Here, we report the coexistence of in-plane and out-of-plane incipient ferroelectricity, along with various phase transitions, in 2D van der Waals layered ${\mathrm{TlGaS}}_2$ single crystal. Detailed investigation of the incipient ferroelectric soft-mode behavior reveals a close correlation between the incipient ferroelectricity and the off-center displacement of $\mathrm{T}{\mathrm{l}}^{1+}$ ions with $6s^2$ lone pairs in ${\mathrm{TlGaS}}_2$. Anomalies near temperatures of about 75, 120, 180, and 220 K in infrared spectra, together with the absence of anomalies in the temperature-dependent specific heat, indicate the existence of local or weak long-range structural transitions in ${\mathrm{TlGaS}}_2$. Our results provide important experimental evidence for elucidating the phase transitions and coexistence of in-plane and out-of-plane incipient ferroelectricity in 2D layered ${\mathrm{TlGaS}}_2$.

How are the spatial and temporal patterns of information scrambling in locally interacting quantum many-body systems imprinted on the eigenstates of the system's time-evolution operator? We address this question by identifying statistical correlations among sets of minimally four eigenstates that provide a unified framework for various measures of information scrambling. These include operator mutual information and operator entanglement entropy of the time-evolution operator, as well as more conventional diagnostics such as two-point dynamical correlations and out-of-time-ordered correlators. We demonstrate this framework by obtaining numerical results for Floquet Haar-random circuits and by deriving exact results for eigenstate correlations in a minimal model of quantum chaos-Floquet dual-unitary circuits. These results reveal not only the butterfly effect and the information lightcone, but also finer structures of scrambling within the lightcone. Our work thus shows how the eigenstates of a chaotic system can encode the full spatiotemporal anatomy of quantum chaos, going beyond the descriptions offered by random matrix theory and the eigenstate thermalization hypothesis.

Layered transition metal dichalcogenides are an important platform for two-dimensional materials, where the inevitable intrinsic defects provide new degrees of freedom for tuning their physical properties. Based on first-principles calculations, this work systematically investigates the formation energies, charge states, and electronic structural characteristics of $V_{\mathrm{Pt}}, V_{\mathrm{Se}}$, and composite vacancies in monolayer ${\mathrm{PtSe}}_2$. The results indicate that while vacancy formation energies are highly sensitive to chemical potentials, the $V_{\mathrm{Se}}$ structure consistently exhibits the lowest formation energy. The charge defect calculation reveals the stable charge state intervals of $V_{\mathrm{Se}}$ and $V_{\mathrm{Pt}}$ as a function of the Fermi level, thus describing the evolution of the charge states of intrinsic vacancies at different electronic chemical potentials. Climbing Image Nudged Elastic Band calculations reveal high migration barriers for $V_{\mathrm{Se}}$ and $V_{\mathrm{Pt}}$, indicating strongly hindered vacancy diffusion at room temperature, while short ab initio Molecular Dynamics simulations confirm the absence of immediate structural collapse within the simulated time window. Optical property calculations indicate that point defects significantly alter the dielectric response of monolayer ${\mathrm{PtSe}}_2$ and generate new low-energy absorption channels associated with in-gap defect states. These findings provide new insights into defect-mediated electronic and optical property modulation in monolayer ${\mathrm{PtSe}}_2$, offering guidance for its potential device design.

We investigate the Anderson metal-insulator transition in three-dimensional lattices with systematically enhanced local connectivity. By introducing modified cubic lattices with seven- and eight-nearest neighbors (7NN and 8NN) per site, we tune the coordination number in a controlled manner while preserving dimensionality, symmetry class, hopping amplitude, and disorder statistics. Using exact diagonalization of a disordered tight-binding Hamiltonian, we characterize localization through complementary spectral and wave-function diagnostics, including level-spacing statistics and inverse participation ratio (IPR) scaling. Finite-size scaling analyses reveal disorder-driven metal-insulator transitions with critical disorder strengths that increase monotonically from the conventional simple cubic lattice to the 7NN and 8NN realizations. Remarkably, this enhancement cannot be explained by bandwidth broadening alone: The normalized ratio $W_c/B$ increases systematically with coordination number, demonstrating that local connectivity influences localization beyond simple spectral rescaling. Consistent with this interpretation, the modified 8NN lattice exhibits a critical disorder strength nearly identical to that of the conventional body-centered cubic lattice despite its fundamentally different connectivity geometry, suggesting that local connectivity can play an important role in determining the localization threshold, alongside bandwidth and detailed hopping geometry. Energy-resolved IPR maps further reveal mobility-edge-type behavior, showing that enhanced connectivity systematically enlarges the extended region of the spectrum and shifts localization crossover boundaries to higher disorder strengths. Despite these substantial changes in localization thresholds, the correlation-length exponent and multifractal properties remain consistent with the three-dimensional orthogonal universality class. These results demonstrate that controlled modification of local connectivity can provide a powerful route for tuning localization behavior in disordered quantum systems while preserving universal criticality.

Excited states play a central role in determining the physical properties of quantum matter, yet their accurate computation in many-body systems remains a formidable challenge for numerical methods. While neural quantum states have delivered outstanding results for ground-state problems, extending their applicability to excited states has faced limitations, including instability in dense spectra and reliance on symmetry constraints or penalty-based formulations. In this work, we rigorously formalize the framework introduced in [D. Pfau et al., Science 385, eadn0137 (2024)] in terms of Grassmann geometry of the Hilbert space. This allows us to generalize the Stochastic Reconfiguration method for the simultaneous optimization of multiple variational wave functions, and to introduce the multidimensional versions of operator variances and overlaps. We validate our approach on the Heisenberg quantum spin model on the square lattice, achieving highly accurate energies and physical observables for a large number of excited states.

We investigate the impact of quantum and thermal phase fluctuations on the suppression of superconducting order in two-dimensional systems. Within the two-dimensional quantum XY model in the phase representation, where on-site interaction terms govern quantum phase fluctuations, we perform extensive path-integral quantum Monte Carlo simulations. The resulting temperature-interaction phase diagram establishes the presence of a well-defined critical line ending at a quantum critical point at vanishing temperature with no indication of reentrant behavior. We further demonstrate that the resistance above the critical line reproduces the two expected different critical behaviors. For stronger interactions, above the quantum critical point, the system exhibits a crossover to an insulating regime at low temperatures. Finally, Monte Carlo calculations of current-current correlation functions enable us to extract the frequency-dependent conductivity in both superconducting and normal regimes, revealing a finite-frequency response that we attribute to quantum phase fluctuations.

Domain-wall-induced ferroic phases offer an emerging platform for reconfigurable nanoelectronics, yet their microscopic formation mechanisms and switching kinetics remain poorly understood. Here, combining machine-learning interatomic potentials with large-scale molecular dynamics simulations, we reveal that ferrielectric (FiE) phases can spontaneously emerge and grow extensively within antiferroelectric (AFE) ${\mathrm{PbZrO}}_3$ under modest biaxial compression. The AFE–FiE transition is driven by an entropy-dominated stabilization of the FiE structure and is enabled by an exceptionally low transformation barrier that collapses under strain. We further show that FiE domains exhibit polarization reversal via dipole flipping-assisted domain reshaping, featuring a small activation barrier and a robust P–E hysteresis response. These results establish the microscopic origin, energetic hierarchy, and switching pathways of DW-induced FiE phases, open an opportunity for their applications in high-speed, low-power domain-boundary-based nanoelectronic devices.