It is shown that in all types of metallic magnets, the coupling of the order parameter to the conduction electrons leads to an order-parameter susceptibility that is long-ranged at zero temperature. This is true for all known classes of ferromagnets, and also for antiferromagnets and spin-density wave systems, helimagnets, magnetic nematics, and altermagnets. The consequences for the magnetic quantum phase transition vary between different classes of magnets. In almost all three-dimensional (3-d) systems with a homogeneous magnetization, as well as in magnetic nematics and in altermagnets, the long-ranged correlations generically modify the nature of the magnetic quantum phase transition from second order to first order. The only exceptions are noncentrosymmetric ferromagnets with a strong spin-orbit interaction, where the correlations change the order of the transition in two-dimensional systems, but not in 3-d ones. In helimagnets, spin-wave systems, and Néel antiferromagnets, their effect is even weaker and does not change the order of the transition if the ordering wave number is sufficiently large, except in flat-band systems. In systems with quenched disorder, the transition generically is of second order, but the correlations modify the critical behavior. These conclusions are reached by very simple considerations that are based entirely on the single-particle excitations in the nonmagnetic phase and their modifications by a field conjugate to the order parameter, augmented by renormalization-group considerations.

Recently, a high-efficiency thermoelectric candidate SnSe has been experimentally shown to undergo a phase transition induced by femtosecond laser excitation, but the underlying microscopic mechanism has not been fully clarified. Photoinduced phase transitions provide an effective means to disentangle electronic and lattice interactions on ultrafast timescales. Using real-time time-dependent density functional theory combined with occupation-constrained density functional theory methods, we investigate the structural response of SnSe under the excitation of 800 nm ($\hslash \omega =1.55\mathrm{eV}$). While the thermal fluctuations fail to destabilize the Pnma phase, promoting 5.4% of the valence electrons induces a rapid Pnma phase to Immm phase transformation. It is found that photoexcitation can reshape the potential-energy surface from hill-like to well-like and drive directional atomic motion. The dynamics are governed by several coherent phonon modes, such as the ${\mathrm{A}}_g^{\left(1\right)}$ and ${\mathrm{A}}_g^{\left(2\right)}$ modes, which play the dominant role in the phase transition. The transition process can be completed on a subpicosecond timescale, highlighting a carrier-driven, nonthermal mechanism for ultrafast phase control in SnSe. These findings offer valuable insights into regulating the phase behavior of SnSe-based systems under nonequilibrium conditions.

We show how combining a discrete symmetry with topological Hilbert space fragmentation can give rise to exponentially many topologically stable qubits protected by a single discrete symmetry. We illustrate this explicitly with the example of the ${\mathrm{CZ}}_p$ model, where the encoded qubits are prethermally stable to arbitrary symmetry-respecting perturbations for parametrically long times, substantially enhancing the robustness of a recently proposed construction based on nontopological fragmentation. In this model, the encoded qubits naturally come in pairs for which a universal set of transversal logical gates can be performed, ruling out (by the Eastin-Knill theorem) the possibility of using them for quantum error correction. We also comment on the combination of symmetry enrichment and topological fragmentation more generally, and the implications for use of systems exhibiting Hilbert space fragmentation as quantum memories.

We study the spin dynamics in the quasi-2D spin-$1/2$ dimer compound ${\mathrm{Ba}}_2{\mathrm{CuSi}}_2{\mathrm{O}}_6{\mathrm{Cl}}_2$, which exhibits a magnetic field-induced Bose-Einstein condensate (BEC) of triplons. Using nuclear magnetic resonance spin-lattice relaxation rate ($T_1^{-1}$) measurements combined with large-scale quantum Monte Carlo (QMC) simulations, we investigate critical fluctuations across the field-temperature phase diagram. Bridging the behavior observed in 1D and 3D systems, the $T_1^{-1}$ relaxation rate shows a pronounced peak extending well above the Néel temperature $T_N$, indicating strong two-dimensional Berezinskii-Kosterlitz-Thouless (BKT)-type fluctuations. A quantitative match between experimental and theoretical BEC phase boundaries validates an effective XXZ model. The study determines the intrinsic BKT transition temperature $T_{\text{BKT}}$ from QMC, revealing a nearly field-independent $T_{\mathrm{BKT}}/T_N\approx 0.74$. Scaling analysis of the relaxation rate shows critical exponents consistent with 2D universality, and a narrow temperature window is identified where 2D physics dominates. These findings establish ${\mathrm{Ba}}_2{\mathrm{CuSi}}_2{\mathrm{O}}_6{\mathrm{Cl}}_2$ as a model system for exploring BKT dynamics in quantum magnets.

Interfacial symmetry breaking leading to the preferential orbital occupation in complex oxide heterostructures offer effective routes to tailor magnetic anisotropy. We demonstrate the modulation of magnetic anisotropy in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ (LSMO) thin films interfaced with the infinite-layer cuprate ${\mathrm{SrCuO}}_2$ (SCO). Static magnetization measurements show a pronounced in-plane magnetic anisotropy in LSMO/SCO bilayers compared to bare LSMO films, consistent with shifts in the resonance field as a function of the angle in ferromagnetic resonance measurements. In addition, a more than two-fold increase in the Gilbert damping is observed across all LSMO/SCO bilayers relative to the bare LSMO films, further supporting the interfacial modification of magnetic anisotropy and magnetization dynamics. However, inserting a thin ${\mathrm{SrTiO}}_3$ (STO) spacer in the control LSMO/STO/SCO sample exhibits the magnetic response similar to that of bare LSMO. This underscores the key role of the LSMO/SCO interface in the observed enhanced magnetic anisotropy. First-principles density functional theory calculations reveal a relatively larger occupation of the $3d_{x^2-y^2}$ orbital near the Fermi level in LSMO/SCO, accounting for the enhanced in-plane magnetic anisotropy, while ruling out the possibility of Rashba field-induced change in magnetic anisotropy. This work provides a comprehensive understanding of enhanced in-plane magnetic anisotropy and magnetization dynamics in the nonisostructural LSMO/SCO heterostructure.

Spin-wave nonreciprocity, manifested as a frequency difference between counterpropagating modes, underpins many proposed magnonic devices. While this effect is commonly attributed to dipolar interactions or interfacial chirality, the microscopic origin of the frequency shift in nonreciprocal dispersion in magnetic multilayers remains under debate. Here, we analyze the frequency shift of nonreciprocal spin-wave dispersion in planar multilayer heterostructures without Dzyaloshinskii–Moriya interaction. Using a frequency-shift dynamic matrix formalism, we show that the frequency asymmetry cannot generally be ascribed to dipolar effects alone. Instead, once counterpropagating modes differ in their geometric structure along the thickness, interlayer exchange dominates the frequency shift. Applied to representative multilayer systems, we find that the interlayer-exchange contribution exceeds dipolar and intralayer exchange effects by up to two to three orders of magnitude over a broad wave-vector range. Our results establish interlayer exchange as the primary mechanism contributing to the frequency shift in nonreciprocal dispersion in multilayer magnonic systems and provide a quantitative framework for engineering large frequency shifts in nonreciprocal magnonic devices.

We present a systematic high-throughput density-functional-theory investigation of the structural and magnetic stability of 312 substitutional compounds in the magnetic kagome ${AT}_6{X}_6$ family. Our screening confirms the stability of many previously reported structures and predicts several additional stable candidates. Within collinear spin configurations, we find that Fe-based systems predominantly adopt antiferromagnetic ground states, whereas Mn-based analogs exhibit a more balanced distribution between ferromagnetic and antiferromagnetic order. For compounds exhibiting several nearly degenerate collinear configurations, we analyze the nature of their magnetic ground states, assess the possible emergence of noncollinear order, and discuss the limitations and uncertainties inherent to standard density-functional approaches. Our electronic structure analysis further reveals that predicted ferromagnetic kagome systems display characteristic features of topological metals, with rich magnetic configurations that can be tuned by chemical substitution. Overall, these ferromagnetic kagome compounds constitute a broad and still largely unexplored materials platform for the emergence of exciting magnetotransport phenomena.

Developing machine learning models that generalize across diverse chemical compositions remains a fundamental challenge in electronic structure theory. Conventional data-driven approaches often exhibit limited transferability due to their reliance on memorizing potential energy surfaces of specific materials. In this work, we present a Slater-Koster (SK) constrained graph attention neural network, implemented as the Graph Attention Tight-Binding (GATB) model, to learn transferable orbital interaction rules. Unlike standard geometric message passing, our framework explicitly embeds the classical SK tight-binding formalism into the neural architecture as a hard constraint. Specifically, we employ orthogonal Bessel basis functions to parametrize the radial decay of SK bond integrals, enforcing rotational invariance and physical asymptotic behavior. This physics-embedded design forces the model to infer electronic couplings based on atomic species and spatial arrangements rather than overfitting to specific geometries. We demonstrate that GATB achieves robust, zero-shot generalization in constructing Hamiltonians and predicting band structures for transition metal dichalcogenides (TMDCs) with chemical compositions unseen during training. Finally, we deploy the trained model as an open-access online tool to facilitate real-time cloud-based Hamiltonian and electronic structure exploration.

Understanding how different stacking sequences in layered semiconductors respond to external stimuli is crucial for elucidating their optoelectronic behavior and for guiding the design of advanced devices. Here, we report a distinct and anomalous pressure-dependent photoresponse in 2H-${\mathrm{SnS}}_2$ and clarify its fundamental contrast with the 4H polytype. The photocurrent of 2H-${\mathrm{SnS}}_2$ increases by nearly 30-fold up to 2.8 GPa and then decreases at higher pressures, in contrast to the monotonically increasing photocurrent observed in 4H-${\mathrm{SnS}}_2$ over the entire pressure range, indicating that the pressure response is strongly dependent on the stacking sequence. Concurrently, the resistance of 2H-${\mathrm{SnS}}_2$ decreases by more than two orders of magnitude at 9.5 GPa, accompanied by an increase in the carrier density from $6.9\times {10}^{14}$ to $1.8\times {10}^{17}{\mathrm{cm}}^{-3}$. Combined high-pressure measurements indicate that the photocurrent evolution is dictated by the competition between pressure-induced bandgap narrowing and defect-assisted recombination. These findings provide insight into the underlying carrier dynamics in layered semiconductors and highlight the stacking structure as a key determinant of the pressure-driven evolution of their photoelectric behavior.

In Si quantum dot systems, large magnetic field gradients are needed to implement spin rotations via electric dipole spin resonance (EDSR). By increasing the effective electron dipole, flopping mode qubits can provide faster gates with smaller field gradients. Moreover, operating in the strong-driving limit can reduce their sensitivity to charge noise. However, alloy disorder in Si/SiGe heterostructures randomizes the valley energy splitting and the valley phase difference between dots, enhancing the probability of valley excitations while tunneling between the dots, and opening a leakage channel. In this work, we analyze the performance of flopping mode spin qubits in the presence of charge noise and alloy disorder, and we optimize these qubits for a variety of valley configurations in both weak- and strong-charge-noise regimes. When the charge noise is weak, high-fidelity qubits can be implemented across a wide range of valley parameters, provided the electronic pulse is fine-tuned for a given valley configuration. When the charge noise is strong, high-fidelity pulses can still be engineered, provided the valley splittings in each dot are relatively large and the valley phase difference is relatively small. We analyze how charge-noise-induced fluctuations in the interdot detuning, as well as small shifts in other qubit parameters, impact qubit fidelities. We find that strongly driven pulses are less sensitive to detuning fluctuations but more sensitive to small shifts in the valley parameters, which can actually dominate the qubit infidelities in some regimes. Finally, we discuss schemes to tune devices away from poor-performing configurations, enhancing the scalability of flopping mode-based qubit architectures.

Electrical current fluctuations provide a powerful and unconventional probe of band geometry in quantum materials. In particular, intrinsic noise components that are independent of the relaxation time reveal universal band-geometric properties of Bloch electrons. Here, we identify a distinct intrinsic contribution to current noise at second order in the electric field, which is governed by the Berry connection polarizability (BCP), a band-geometric quantity constructed from energy-weighted interband components of the quantum metric. This effect arises from field-induced modifications to Bloch wave functions and band energies, and it contributes to both the longitudinal and transverse noise components. Applying our theory to CuMnAs, we demonstrate that thermal noise provides a direct signature of BCP in crystalline solids.

The debate over whether the charge density wave (CDW) in ${\mathrm{TiSe}}_2$ originates from spontaneous exciton condensation or the Jahn-Teller effect persists. Although this material has been extensively studied as a candidate excitonic insulator, few investigations have focused on whether spontaneous excitons exist within its CDW phase. In this work, we employ first-principles calculations combined with effective exciton models to systematically investigate the single-electron band gap and exciton binding energy in the CDW phase of monolayer ${\mathrm{TiSe}}_2$, comparing these results with experimentally observed band gaps. Our findings indicate that the single-electron band gap provides a reasonable experimental explanation, while spontaneous exciton condensation alone cannot account for the magnitude of the experimentally observed band gap. Notably, we find that ionic screening plays a pivotal role here, in contrast to the nearly negligible effect in many transition-metal dichalcogenides. While neglecting ionic screening is physically reasonable when calculating photoexcited excitons, we argue that it should be included when considering spontaneously condensed excitons. Based on these findings, we conclude that spontaneously generated and condensed excitons do not exist in the CDW ${\mathrm{TiSe}}_2$ monolayer.

We investigate the imaginary-time relaxation critical dynamics of the two-dimensional transverse-field Ising model using infinite projected entangled pair states (iPEPS) with the full-update strategy. Simulating directly in the thermodynamic limit, we explore the relaxation process near the critical point with two types of initial states: a fully polarized state and a product state with a small magnetization. For the fully polarized state, the magnetization shows a power-law scaling $M\propto {\tau }^{-\beta /\left(\nu z\right)}$ in the imaginary-time evolution, from which both the critical point and critical exponent can be determined with high accuracy. For the nearly paramagnetic state, the relaxation process exhibits a behavior of $M\propto {\tau }^{\theta }$ with $\theta =0.1958$ being the critical initial-slip exponent, which is in good agreement with that obtained from the dynamic scaling of the self-correlation in the quantum Monte Carlo method. These universal features emerge well before the system converges to the ground state, demonstrating the efficiency of imaginary-time evolution for probing quantum criticality. Our results demonstrate that iPEPS can serve as a robust and scalable method for studying dynamical critical phenomena in two-dimensional quantum many-body systems.

Uranium $L_3$ and $M_4$ X-ray absorption spectra, taken in a high-energy resolution fluorescence detection mode on a heavy-fermion antiferromagnet ${\mathrm{UPd}}_2{\mathrm{Cd}}_{20}$, display two absorption edges, each associated with a different valence state, namely $5f^2$ and $5f^3$. Due to a single type of U position in the crystal structure it is strongly suggestive of slow $f^2\text{−}{f}^3$ fluctuations on a timescale longer than the characteristic time of the spectroscopy technique. Unlike $4f$ systems, in which such fluctuations lead to a destruction of magnetism due to the involvement of one nonmagnetic state, the $f^2$ and $f^3$ states in U are both possibly magnetic, allowing for magnetic ordering in the fluctuating state. A valence fluctuation state has been speculated in the past in the context of U intermetallic compounds, but it was not corroborated by a microscopic technique. This evidence can bring more light into emergent phenomena observable in U systems at the verge of $5f$ localization.

As a consequence of their spin-orbit entangled ground state, many $5d^5$ iridate materials display a peculiar double-peak structure in optical transport quantities, such as absorption and conductivity. Their common interpretation is based on the presence of Hubbard subbands in the half-filled $j_{\mathrm{eff}}=1/2$ manifold. Herein, we challenge this picture, proposing a scenario based on the presence of spin-polaron (SP) quasiparticles, and assigning a dominant SP character to the first peak. We illustrate it by taking the materials ${\mathrm{Ba}}_2{\mathrm{IrO}}_4$ and ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ as paradigmatic examples, which we investigate within the dynamical mean-field theory and the self-consistent Born approximation. Both theories reproduce nontrivial features revealed by angle-resolved photoemission spectroscopy and optical transport measurements, supporting our interpretation. In the case of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ we show how the SP scenario survives in the low-doped regime. Similar optical transport fingerprints are expected to be found in the wider class of $5d^5$ iridates and more generally in strongly correlated antiferromagnetic regimes, such as those found in cuprates.

Ferroelectric materials hold great promise for next-generation electronic devices, yet their practical implementation is often impeded by issues such as fatigue and loss. Unraveling polarization dynamics is pivotal to overcoming these hurdles. In this work, we employ a first-principles-based effective Hamiltonian formalism combined with molecular dynamics simulations to investigate the influence of depolarization fields on 180° domain switching dynamics in ferroelectric thin films. Two distinct switching pathways are identified: under near-ideal charge screening (screening factor $\beta =1.00$), domain switching proceeds via continuous shrinking of the original domain through inward propagation of 180° domain walls (referred to as “domain-shrinking switching”); under relatively poor surface charge screening $(\beta =0.90)$, switching is initiated by nucleation and growth of newly reversed domains in the central region of the original domain, with the outward polarization of the original domain being pinned initially and eventually vanishing (termed “central nucleation switching with pinned boundaries”). A continuous transition between these pathways occurs as β increases from 0.90 to 1.00. A phase diagram mapping the dependence of the switching pathway on charge screening conditions is constructed. Furthermore, the origin of these two distinct pathways is elucidated from a microscopic perspective, focusing on polarization reversal energy barriers and effective electric field distributions. This study highlights the decisive role of interfacial electrostatic screening in modulating domain wall dynamics and provides theoretical guidance for designing tunable ferroelectric devices.

We investigate the effect of heavy-tailed control statistics on time crystals, driven many-body systems where subharmonic order is governed by fluctuations rather than Gaussian noise. We emphasize that this work does not introduce a new phase of matter, but instead characterizes the decay dynamics of subharmonic order under heavy-tailed control fluctuations. Lévy-distributed pulse errors lead to a nonanalytic scaling of the decay rate, providing a direct dynamical signature of rare-event fluctuations. When the drive timing is heavy tailed, renewal dynamics produces algebraic decay without a characteristic timescale. These results show that heavy-tailed control statistics place time-crystalline dynamics in a distinct dynamical regime governed by rare events rather than diffusive dephasing.

Discrete time crystals (DTCs) are nonequilibrium phases of matter that break the discrete time-translation symmetry and are characterized by a robust subharmonic response in periodically driven quantum systems. Here, we explore the DTC, stabilized by the Floquet strong Hilbert space fragmentation, in a disorder-free periodically kicked XXZ spin chain. We numerically show the period-doubling response of the conventional DTC order, and uncover a multiple-period response with beating dynamics due to the coherent interplay of multiple $\pi$ pairs in the Floquet spectrum of small-size systems. The lifetime of the DTC order exhibits independence of the driving frequency and a power-law dependence on the ZZ interaction strength. It also grows exponentially with the system size up to a critical imperfection, as a hallmark of the strong fragmentation inherent to the Floquet model. We analytically reveal the approximate conservation of the magnetization and domain-wall number in the Floquet operator for the emergent strong fragmentation, which is consistent with numerical results of the dimensionality ratio of symmetry subspaces. The rigidity and phase regime of the DTC order are identified through finite-size scaling of the Floquet-spectrum-averaged mutual information, as well as via dynamical probes. Our work establishes the Floquet Hilbert space fragmentation as a disorder-free mechanism for sustaining nontrivial temporal orders in out-of-equilibrium quantum many-body systems.

We present an ab initio investigation of magnetic exchange interactions using the spin-spiral method as implemented in the VASP code, comparing fully self-consistent (SC) total-energy calculations with non-self-consistent (NSC) band-energy evaluations within the same computational framework. Using representative $3d$ ferromagnets (Fe, Co, Ni) and Mn-based full Heusler compounds, we compute magnon dispersion relations and extract real-space Heisenberg exchange parameters from the Fourier transformation of spin-spiral energies. Curie temperatures are subsequently estimated within the mean-field and random-phase approximations. The SC approach yields exchange parameters and magnon spectra in excellent agreement with experimental and previous theoretical data, confirming its quantitative reliability across different classes of magnetic systems. In contrast, the NSC approach based on a frozen-potential approximation exhibits systematic quantitative deviations: it overestimates spin-spiral energies and exchange couplings in high-moment systems (bcc Fe and Mn-based Heuslers) while underestimating them in low-moment fcc Ni. The magnitude of these discrepancies increases with the magnetic moment size and can exceed several hundred percent in high-moment compounds. Our results demonstrate that while NSC evaluations are computationally efficient, fully SC spin-spiral calculations are essential for obtaining quantitatively reliable exchange interactions within the projector augmented-wave framework.