We report an experimental study of the disordered Su-Schrieffer-Heeger (SSH) model, implemented in a system of coaxial cables, whose radio frequency properties map onto the SSH Hamiltonian. By measuring multiple chains with random hopping terms, we demonstrate the presence of a topologically protected state, with frequency variation of less than 0.2% over the ensemble, evidence of near-perfect chiral symmetry. When the ends of the chains are connected to form loops, we observe a topological phase transition, characterized by the closure of the band gap and the appearance of states that are delocalized, despite the strong disorder.

The prevalence of sparsity in the Fock space graph of interacting many-body systems motivates an investigation into the spectral statistics of sparse random matrices with on-site disorder. We numerically determine the delocalization-localization transition in the ground state as a function of the sparsity. The short-range energy correlation in the bulk indicates that the Anderson transition at infinite temperature occurs at the critical percolation limit of the sparse graph. By analytically deriving the energy moments and calculating the shifted kurtosis, we show that the critical sparsity threshold matches the Anderson transition. Furthermore, long-range energy correlations in the bulk spectrum reveal a Thouless energy scale, suggesting a broad nonergodic regime within the delocalized phase.

${\mathrm{RuO}}_2$, proposed as a potential altermagnet, is expected to serve as a new-generation spintronic material enabling precise control of spin transport. However, the existence of magnetic order in ${\mathrm{RuO}}_2$ has recently been widely questioned. Here, based on first-principles calculations, we systematically investigate the magnetic order in ${\mathrm{RuO}}_2$ under epitaxial strain. We find that a modest global strain can drive ${\mathrm{RuO}}_2$ from a nonmagnetic state to an antiferromagnetic state. Furthermore, near the strain-induced magnetic critical point, a modest local distortion can stabilize a spin-density-wave state over the antiferromagnetic state, with an energy difference on the order of $10-100\mu \text{eV}$ and a characteristic wavelength of about 7–10 nm. Our study provides a unified microscopic picture for the experimental controversy regarding altermagnetism in ${\mathrm{RuO}}_2$, and highlights the key roles of global strain and local distortion in tuning ${\mathrm{RuO}}_2$ magnetism and spin transport.

NaB(CN)${}_4$ exhibits giant negative thermal expansion (NTE) that is closely associated with low-frequency phonons with large negative Grüneisen parameters. Although compression-induced softening of negative-Grüneisen phonons can modify lattice thermal conductivity (${\kappa }_{\mathrm{L}}$), how NTE-active phonon modes differently influence the population (${\kappa }_{\mathrm{pop}}$) and coherence (${\kappa }_{\mathrm{coh}}$) contributions to ${\kappa }_{\mathrm{L}}$ remains unclear. Here, we combine perturbative high-order anharmonic lattice dynamics and homogeneous nonequilibrium molecular dynamics (HNEMD) simulations accelerated by a neuroevolution potential (NEP) to investigate compression-dependent thermal transport in NaB(CN)${}_4$. Both approaches capture a compression-induced decrease in ${\kappa }_{\mathrm{L}}$. At 300 K, NEP–HNEMD simulations show that ${\kappa }_{\mathrm{L}}$ decreases from $1.05\pm 0.03$ to $0.49\pm 0.01\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ over the structurally intact strain range examined up to $4\%$. In the weak-compression regime, the reduction is dominated by the suppression of ${\kappa }_{\mathrm{pop}}$. NTE-active framework modes near 2.5 THz soften under compression, reducing phonon group velocities and increasing the three-phonon scattering phase space. By contrast, the compression-induced difference in ${\kappa }_{\mathrm{coh}}$ is mainly concentrated near 7.5 THz, where the relevant phonon pairs harden. Nevertheless, ${\kappa }_{\mathrm{coh}}$ increases only slightly and remains secondary to ${\kappa }_{\mathrm{pop}}$. These contrasting responses reveal a nonuniform phonon-spectrum reconstruction under compression in which strain selectively reshapes the population and coherence channels of heat transport, linking NTE-active phonons to anomalous thermal transport in NaB(CN)${}_4$.

We solve the two-electron problem on a square lattice with $d$-wave altermagnetism, considering both on-site and nearest-neighbor attractive interactions. The altermagnetic spin-splitting in the single-particle dispersion naturally gives rise to a ground state of two-electron bound pairs with nonzero center-of-mass momentum. The emergence of finite-momentum bound states suggests that altermagnetic spin splitting may favor pairing at nonzero center-of-mass momentum, which could be relevant for proposed Fulde-Ferrell-Larkin-Ovchinnikov superconductivity in altermagnetic systems. Additionally, when the nearest-neighbor attraction is strong, the resulting finite-momentum bound pairs exhibit a mixture of both spin-singlet and spin-triplet characteristics, suggesting the possibility of unconventional superconductors, where spin-singlet and spin-triplet pairings coexist.

A central question beyond the Landau paradigm is the nonperturbative critical theory of the symmetric mass generation (SMG) transition, where strong interactions gap Dirac fermions in $2+1$ dimensions without triggering spontaneous symmetry breaking or topological order. Sign-problem-free studies have previously found fermion mass generation without bilinear condensation in related models, but the fermionic scaling properties of Hamiltonian SMG transitions remain incompletely characterized. Using sign-problem-free projector determinant quantum Monte Carlo simulations of a bilayer honeycomb lattice model with $\mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)/{\mathbb{Z}}_2$ symmetry and linear sizes up to $L=21$, we find evidence for a direct continuous transition: the single-particle and bosonic gaps open consistently near $J_c\approx 2.6$, with correlation-length exponent $\nu =1.14\left(2\right)$ from the better-converged fermionic analysis, while all 19 symmetry-inequivalent local fermion-bilinear multiplets remain disordered. We obtain an unbiased estimate of the fermion anomalous dimension, ${\eta }_{\psi }=0.071\left(1\right)$, which differs from the large-$N$ prediction (${\eta }_{\psi }\approx 0.595$) and the variational Monte Carlo estimate (${\eta }_{\psi }\approx 0.62$), thereby constraining candidate descriptions of SMG criticality. A comparison with a related $\mathrm{Spin}\left(5\right)\times \mathrm{U}\left(1\right)/{\mathbb{Z}}_2$ model, which develops an intermediate excitonic phase, illustrates how the symmetry content controls competing bilinear orders.

The difficulty of determining cation concentrations and oxygen stoichiometry in infinite-layer nickelate thin films has so far prevented clear experimental identification of the nickel electron configuration in the superconducting phase. We used soft x-ray absorption spectroscopy to study the successive changes in ${\mathrm{PrNiO}}_x$ thin films at various intermediate stages of topotactic reduction with $x=2–3$. By comparing the $\mathrm{Ni}L$-edge spectra to single- and double-cluster ligand-field calculations, we find that none of our samples exhibits a pure $d^9$ configuration. Our quantitative analysis using the charge sum rule shows that even when films are maximally reduced, the spatially averaged number of nickel $3d$ holes is 1.38. Superconducting samples have even higher values, calling into question the previously assumed limit of hole doping. Concomitant changes in the oxygen $K$-edge absorption spectra upon reduction indicate the presence of oxygen $2p$ holes, even in the most reduced films. Overall, our results suggest a complex interplay of hole-doping mechanisms resulting from self-doping effects, structural defects, and oxygen nonstoichiometry.

We extend the Kajueter-Kotliar [Phys. Rev. Lett. 77, 131 (1996)] iterated perturbation theory (KK-IPT) away from half-filling to nonequilibrium steady states. We benchmark the resulting nonequilibrium KK-IPT approach against the auxiliary master equation approach (AMEA), whose accuracy is controlled in and out of equilibrium. As expected, in equilibrium, KK-IPT reproduces the AMEA results for different fillings with high accuracy at the level of both spectral properties and electron densities. Out of equilibrium, we study quantum transport across a correlated impurity and compute the differential conductance and spectral functions. We find very good agreement between nonequilibrium KK-IPT and AMEA in the parameter regime where the latter is reliable, in particular at moderate temperatures and biases. Although a controlled benchmark is not available in the low-temperature, low-bias regime, where AMEA becomes less reliable, we show that this nonequilibrium KK-IPT impurity solver satisfies the exact spectral sum rules for the first and second moments to high accuracy throughout the entire parameter range studied. These results support nonequilibrium KK-IPT as an approximate description of nonequilibrium steady states away from half-filling. At the same time, comparing against AMEA the double occupancy obtained from the nonequilibrium Galitskii-Migdal expression for the interaction energy shows that the deviation from AMEA remains small near half-filling for moderate and large values of the bias, but grows markedly away from half-filling, delineating the regime in which the method can be trusted quantitatively rather than merely qualitatively.

Muonium (Mu) is widely used as a model for isolated hydrogen in condensed matter, but whether its electronic state is truly equivalent to that of hydrogen remains to be tested with an orbital-sensitive probe. Here we use double electron-muon resonance to determine the electron $g$ values of the paramagnetic Mu center in rutile ${\mathrm{TiO}}_2$ for magnetic fields along [100], [110], and [001] directions. The obtained $g$ values closely follow those of the H-related ${\mathrm{Ti}}^{3+}$ paramagnetic center in both magnitude and anisotropy. This agreement tests the Mu-H correspondence at the level of the Ti $3d$ electronic state and supports a common localized ${\mathrm{Ti}}^{3+}$ electronic core for the two centers.

We study the dynamics of a spin-polarized wave packet in a disordered Rashba two-dimensional (2D) electron gas and identify a jittery quantum boomerang effect in which longitudinal and transverse motion return to the origin through fundamentally distinct mechanisms. Starting from an initial state with finite momentum along $x$ and spin polarized along $z$, we calculate the time evolution by combining a Chebyshev expansion of the time-evolution operator with a disorder ensemble average. In the weak-scattering regime, equations of motion derived from the quantum kinetic equation reproduce the numerical trends and show that impurity scattering acts as a viscous damping mechanism that suppresses the transient Zitterbewegung and drives the transverse displacement back to $y=0$ at long times. Conversely, the longitudinal dynamics show a Drude-like saturation at weak disorder. These results are consistent with the vanishing intrinsic spin Hall conductivity in the disordered Rashba model and with experimental observations of a transient intrinsic spin Hall effect in the time domain. As disorder increases, the longitudinal dynamics evolve to a partial return toward the origin, which signals a transition from weak antilocalization to Anderson localization in 2D.

We propose and characterize protocols to engineer exact quantum revivals, discrete time crystals (DTCs), and entanglement oscillations in the periodically driven central spin model. While period-doubling DTCs have been observed in this system before, we uncover a unifying interaction-induced echo mechanism underlying several distinct dynamical regimes. We first demonstrate that this echo can enable exact period-doubling revivals when the Ising interaction strength, $\lambda$, between the central spin and the $N_{\mathrm{sat}}$ satellite spins is tuned to $2\pi$. Notably, these revivals persist for arbitrary $N_{\mathrm{sat}}$ and transverse field $g$. This not only stabilizes the DTC response over a wide parameter regime, but also leads to a dynamical freezing regime. Furthermore, when $\lambda =(2m+1)\pi$ and $g=(2n+1)\pi /2$ ($\forall m,n\in \mathbb{Z}$), this echo induces a Clifford group structure. Consequently, higher-period revivals emerge that naturally steer the system through an entangled manifold of Bell-cat and spin-cat states. We establish that due to parity-dependent phases accumulated during the echo, the recurrence period is $12T\left(24T\right)$ for even (odd) $N_{\mathrm{sat}}$. Finally, we demonstrate that the multipartite entanglement generated by the Clifford dynamics can be harnessed for multiparameter metrology, with odd $N_{\mathrm{sat}}$ enabling Heisenberg-limited sensitivity.

I investigate the stability of the spin-orbital liquid described by the Yao-Lee model in the presence of multiple perturbations that naturally arise in a recently proposed microscopic realization. While most perturbations are irrelevant and do not qualitatively alter the exact solvability, we find that the Kitaev interaction plays a special role: it couples to the ${\mathbb{Z}}_2$ gauge field and renders the visons mobile.

We investigate Majorana current induced by charge current in Kitaev magnets coupled with graphene through the mechanism by which Majorana fermions in the Kitaev magnet are dragged by electrons in graphene. We calculate Majorana current density based on the perturbation with respect to a Kondo-type Majorana-electron coupling and obtain an analytical expression of the Majorana current induced by charge current, indicative of electronic control of charge-neutral Majorana fermions. We also discuss Majorana heat current induced by charge current and give estimations of their magnitudes.

The $t$ model represents the Hubbard model in the limit $U\to \infty$ and is one of the basic models of strongly correlated electrons. On a one-dimensional chain, the model is integrable, and its charge dynamics is equivalent to that of free spinless fermions. However, within its dynamics the sequence of spins is frozen, implying Hilbert-space fragmentation and nontrivial spin dynamics. We focus primarily on perturbed versions of the model in which the perturbations break integrability while preserving fragmentation. Considered examples of such perturbations are spin-dependent hopping and additional spin interaction. We show that these models exhibit a variety of spin-transport regimes. In contrast to the integrable model, which displays either ballistic transport or dissipationless diffusion, the perturbed systems exhibit either normal diffusion or subdiffusion. Due to Hilbert-space fragmentation, spin transport is mediated by charge transport in all cases considered. This leads to a characteristic dependence on the magnetization, most notably resulting in subdiffusive spin transport in the grand-canonical ensemble of the perturbed model. The underlying mechanism is distinct from the subdiffusion observed in disordered systems or in models with dipole conservation.

We investigate light transport in three-dimensional disordered media composed of irregular dielectric particles using large-scale full-wave simulations. For subwavelength particles with a size parameter $kr\approx 1$ and high refractive index contrast, we observe a crossover from diffusion to a regime characterized by nonexponential decay of time-resolved transmission as disorder increases. The corresponding time-dependent diffusion coefficient decreases with time and approaches a $t^{-1}$ scaling at long times. This dynamical slowdown is accompanied by the emergence of spectrally isolated transmission resonances with Thouless conductance below unity, indicating the dominance of long-lived modes with weak spectral overlap. The late-time near-field maps reveal evolving, nonpropagating clusters of intensity hot spots. Together, the transport, spectral, and near-field signatures provide converging numerical evidence consistent with the onset of Anderson localization of light in three-dimensional disordered dielectric media.

The giant inverse magnetocaloric effect (MCE) observed in Heusler alloys holds significant promise for magnetic refrigeration. However, its practical application is hampered by hysteresis, irreversibility, and, critically, the degradation of MCE under cyclically applied magnetic fields. In this study, we propose a paradigm shift: instead of suppressing the irreversibility of the martensite-austenite magnetostructural phase transition (MSPT), we propose to control and utilize it. We present a comprehensive investigation of the irreversible phase transition dynamics in the ${\mathrm{Ni}}_{47}{\mathrm{Mn}}_{40}{\mathrm{Sn}}_{12}{\mathrm{Cu}}_1$ alloy, employing direct measurements of the adiabatic temperature change $\left(\mathrm{\Delta }{T}_{\mathrm{ad}}\right)$ in cyclic fields up to 8 T, in situ XRD analysis, and first-principles DFT and Monte Carlo calculations. Our findings reveal that the irreversibility of the phase transition contributes an additional component to the giant inverse MCE, enhancing the overall effect by up to 35%. We identify a critical dependence of the magnitude and sign of $\mathrm{\Delta }{T}_{\mathrm{ad}}$ on the magnetic field sweep rate and thermal history, which is governed by nucleation and growth kinetics. Rapid cooling is shown to induce to kinetic arrest, resulting in a mixed two-phase state with comparable martensite and austenite fractions, where the direct and inverse MCE contributions compensate each other, leading to the “collapse” of the giant inverse MCE. Our results demonstrate a new route to enhance and stabilize the giant inverse MCE through the controlled utilization of irreversibility and the optimization of the operating cycle kinetics. This approach paves the way for the rational design of magnetic materials and operational protocols for high-performance magnetic refrigerators.

A theoretical model for calculating the linear coupled elastic and magnetic modes of a layered structure is presented. Based on the partial wave formalism, which has been previously employed to treat acoustic and magnetic problems separately, this method incorporates the magnetoelastic interaction into the equations of motion of both subsystems to achieve a self-consistent solution. The dependence of all dynamic variables on the out-of-plane direction is fully taken into account, alongside the main physical interactions: piezoelectricity, bulk and interface anisotropies, external magnetic fields, exchange, and damping. The frequencies of the discrete spectrum are determined as a function of the parallel wave vector and system parameters, yielding the corresponding mode profiles and energy contributions. The model is then applied to two systems characterized by thick and thin films, which have been previously investigated experimentally in the literature. Furthermore, a model calculation is presented to illustrate a magnetoelastically driven hybridization between Sezawa and Love-type modes in an elastically isotropic medium.

We report on the epitaxial growth of antiferromagnetic ${\mathrm{Mn}}_2\mathrm{Au}$ on a Nb(001) substrate capped with a pseudomorphic layer of gold. We observe a layer-by-layer growth by means of medium-energy electron diffraction and confirm stoichiometry and surface structure by Auger electron spectroscopy and low-energy electron diffraction. Evaporation of 15 ML of ferromagnetic Fe on 12–17 ML of ${\mathrm{Mn}}_2\mathrm{Au}$ results in an exchange-coupled bilayer system with an exchange-bias shift that can be set by field-cooling from 400 K. Areas with and without exchange bias, with domain sizes in the range of tens of $\mu \mathrm{m}$, are identified by Kerr microscopy. Postannealing the sample at or above 450 K after ${\mathrm{Mn}}_2\mathrm{Au}$ layer growth decreases the fraction of areas where Fe magnetically couples to ${\mathrm{Mn}}_2\mathrm{Au}$. We suggest that exchange coupling to an interfacial Fe layer depends on the interface termination of ${\mathrm{Mn}}_2\mathrm{Au}$ or on the chemical order in the ${\mathrm{Mn}}_2\mathrm{Au}$ layer. Our findings provide insight into the growth process of ${\mathrm{Mn}}_2\mathrm{Au}$ and the coupling to an Fe layer. Our results point out the importance of growth, interface quality, and termination for the magnetic properties of a ${\mathrm{Mn}}_2\mathrm{Au}/\mathrm{Fe}$ bilayer, which may help to improve material properties for spintronic applications.