A recent work [Mierzejewski et al., Phys. Rev. B 107, 045134 (2023)] observed “quasiballistic spin transport”—long-lived and transiently ballistic modes of the magnetization density—in numerical simulations of infinite-temperature XXZ chains with power-law exchange interactions. We develop an analytical theory of such quasiballistic spin transport. Previous work found that this effect was maximized along a specific locus in the space of model parameters, which interpolated smoothly between the integrable Haldane-Shastry and XX models and whose shape was estimated from numerics. We obtain an analytical estimate for the lifetime of the spin current and show that it has a unique maximum along a different locus, which interpolates more gradually between the two integrable points. We further rule out the existence of a conserved two-body operator that protects ballistic spin transport away from these integrable points by proving that a corresponding functional equation has no solutions. We discuss connections between our approach and an integrability-transport conjecture for spin.

We apply a first-principles-based atomistic model to investigate the ${\mathrm{BaTi}}_{1-x}Z{r}_x{O}_3$ phase diagram, focusing on both macroscopic and local structural changes. Our approach, which combines molecular dynamics with machine learning techniques, accurately captures the influence of Ti and Zr cations on their local environment and its evolution with composition and temperature. The computed phase diagram shows excellent agreement with existing experimental and theoretical data. Beyond reproducing known results, our analysis reveals that the behavior of the solid solution across different compositions and temperatures can be understood in terms of coexisting Ti cells with different symmetries, whose stability depends on the local B-site configuration. This local-phase-based approach provides a unified description of the distinct regions of the solid solution—including ferroelectric, relaxor, and dipolar glass phases—and captures the continuous evolution from one regime to another. Our findings demonstrate how atomic-level distortions drive the complex macroscopic behavior of the material.

Hydrogen bond symmetrization is a fundamental pressure-induced transformation in which the distinction between donor and acceptor sites vanishes, resulting in a symmetric hydrogen-bond network. While extensively studied in pure ice—most notably during the ice VII to ice X transition—this phenomenon remains less well characterized in hydrogen hydrates. In this work, we investigate hydrogen bond symmetrization in the high-pressure phases of hydrogen hydrates $({\mathrm{H}}_2\text{−}{\mathrm{H}}_2\mathrm{O} \text{and} {\mathrm{D}}_2\text{−}{\mathrm{D}}_2\mathrm{O})$ through a combined approach of Raman spectroscopy and first-principles quantum atomistic simulations. We focus on the C2 and C3 filled-ice phases, using both hydrogenated and deuterated water frameworks. Our results reveal that quantum fluctuations and the interaction between the encaged ${\mathrm{H}}_2$ molecules and the host lattice play a crucial role in driving the symmetrization process. Remarkably, we find that in both C2 and C3 phases hydrogen bond symmetrization occurs via a continuous crossover at significantly lower pressures than in pure ice, without any change in the overall crystal symmetry. These findings provide insight into the quantum-driven mechanisms of bond symmetrization in complex hydrogen-bonded systems under extreme conditions.

Nonsaturated extremely large magnetoresistance (XMR), quantum oscillation (QO), and nontrivial Berry phase have been observed in many exotic quantum materials. But the underlying mechanisms driving these phenomena remain a puzzle. In this work, we present a comprehensive investigation of the structural, magnetic, XMR, and QO study of high-quality PrP, PrAs, and PrSb single crystals, alongside density functional theory $\left(\mathrm{DFT}\right)+U$ calculations x-ray diffraction analyses indicate that the flux-grown high-quality PrX (where X represents P, As, or Sb) system exhibits a simple rock-salt type structure with R-3m symmetry (No. 225). Heat capacity and susceptibility measurements find that the 4f electrons of $\mathrm{P}{\mathrm{r}}^{3+}$ ions in all three compounds are localized and the PrX system shows a Van Vleck paramagnetic ground state without any structure transition. Quantum transport measurements reveal nearly quadratic behavior in the magnetoresistance and significant angular and temperature-dependent Shubnikov–de Haas oscillations, with small effective mass ${\mathrm{m}}_0$ of multiband charge carriers. Fast Fourier transformation analyses yield an electron pocket (α band) located at the X point predominantly associated with the Pr d electrons, and two types of hole pockets (the outer β and inner γ pockets) at the Γ point, which primarily arise from the p orbitals of As or Sb. Comparison with $\mathrm{DFT}+U$ calculations indicate a crucial role of the 4f Coulomb interaction in influencing the topology of the band structures, particularly the presence of band crossing points. Our work provides a basis for in-depth investigations into the XMR, quantum oscillations, and Berry phase associated with band topology in lanthanum monopnictides and other innovative quantum material systems.

The quantum Mpemba effect (QMPE), an anomalous relaxation phenomenon, has been demonstrated in both closed and open Hermitian quantum systems. While some studies have linked the QMPE to Liouvillian exceptional points—non-Hermitian features emerged at the Liouvillian level—in open Hermitian quantum systems, it remains largely unexplored whether the QMPE can occur in intrinsic non-Hermitian systems, where non-Hermiticity is inherent at the Hamiltonian level. Here, we demonstrate unequivocally the occurrence of QMPE in experimentally realizable parity-time symmetric qubit systems immersed in a bosonic bath. Using established quantifiers for QMPE, we show numerically that the QMPE persists across parameter regimes both near and far from Hamiltonian and Liouvillian exceptional points, but disappears entirely when a Hermitian Hamiltonian is restored. Interestingly, neither Hamiltonian nor Liouvillian exceptional points demarcate the boundaries of the QMPE regime. To complement numerical results, we develop an analytical description based on a long-time approximation of the relaxation dynamics of quantifiers. This approach allows us to decipher the number of intersections between two dynamical trajectories of quantifier starting from two initial conditions in the validity regime of the long-time approximation, thereby providing additional information that delineates the parameter regimes supporting the genuine QMPE. We further demonstrate the robustness of QMPE against increasing the number of qubits and dephasing effect. Our findings not only broaden the scope of the QMPE but also suggest its intricate interplay with non-Hermitian features beyond exceptional points.

We investigate the nonlinear optical response of bulk ZnO under intense short-wave infrared excitation, focusing on the interplay between high-harmonic generation (HHG) and photoluminescence (PL). While HHG exhibits nonperturbative intensity scaling and a spectral blueshift consistent with plasma-induced refractive index changes, the PL signal shows a pronounced superlinear increase and a redshift, attributed to a combination of exciton-exciton scattering and phonon-assisted exciton recombination emission. A similar PL response under above-bandgap excitation supports its intrinsic origin. Spectral analysis of the HHG emission reveals an intensity-driven transition in the characteristics of the fifth harmonic, indicating a change in the underlying generation mechanism. These findings establish PL and spectral HHG analysis as complementary probes of strong-field and many-body effects in wide-bandgap semiconductors.

Floquet engineering offers a versatile platform for realizing nonequilibrium topological phenomena in both quantum and classical-wave systems. Departing from common approaches that induce Floquet topological phases by tailoring hoppings or on-site potentials, we present an alternative scheme utilizing periodic modulation of the magnetic flux to induce rich topological features. Specifically, we consider two types of flux-dressed quasi-one-dimensional lattices: one with chiral symmetry and one with inversion symmetry. Using a two-step flux modulation protocol, we demonstrate the emergence of topological zero and $\pi$ modes in both systems. In the chiral-symmetric model, the bulk topology is fully described by the conventional and dynamical winding numbers, preserving the bulk-boundary correspondence. In the inversion-symmetric case, the phases are characterized by the quantized Zak phase, but edge modes may vanish even in topologically nontrivial phases. We further show that this breakdown can be recovered by double modulation. Our findings establish periodic flux modulation as a versatile and experimentally feasible tool for engineering Floquet topological matter.

Ferrimagnetism typically emerges from chemically distinct magnetic ions or the same element at two inequivalent crystallographic sites, rendering unequal moments. In contrast, ${\mathrm{Ni}}_4{\mathrm{Nb}}_2{\mathrm{O}}_9$ has been recently discovered to show a different mechanism, where identical ${\mathrm{Ni}}^{2+}$ ions with the same ligand coordination develop unequal magnetic moments purely due to differences in local environments. Here, we investigate the microscopic origin of this emergent mechanism through a synergy of powder neutron diffraction, inelastic neutron scattering, and first-principle-based calculations. We demonstrate that the ${\mathrm{Ni}}_A$ and ${\mathrm{Ni}}_B$ sublattices, while sharing the same nominal valence, differ in their magnetic dimensionality: ${\mathrm{Ni}}_A$ forms quasi-one-dimensional chains with enhanced $p\text{−}d$ hybridization and a reduced magnetic moment, whereas ${\mathrm{Ni}}_B$ retains a nearly two-dimensional geometry and a full $S=$ 1 moment. Our results underscore the pivotal role of spin dimensionality and local structural distortions in stabilizing ferrimagnetism in systems with electronically equivalent magnetic ions.

We report a detailed high-field/high-frequency ferromagnetic resonance (HF-FMR) study of low-energy magnon excitations in the van der Waals ferromagnet ${\mathrm{Fe}}_{2.92\left(1\right)}{\mathrm{Ge}}_{1.02\left(3\right)}{\mathrm{Te}}_2$. At $2\mathrm{K}$, the field dependence of the magnon branches is well described by a semiclassical domain-based model, from which we extract key microscopic parameters including the anisotropy gap $\mathrm{\Delta }=170\left(4\right)\mathrm{GHz}$, the anisotropy field $B_{\mathrm{A}}=5.85\left(8\right)\mathrm{T}$, and the effective $g$-factor $g_{\mathrm{ab}}=g_{\mathrm{c}}=2.07\left(4\right)$. Furthermore the uniaxial anisotropy constant is determined to be $K=10.50\left(23\right)\times {10}^6\text{erg}/{\mathrm{cm}}^3$. Anisotropic short-range magnetic order persists above $T_{\mathrm{C}}$ up to approximately $270\mathrm{K}$, as evidenced by a finite anisotropy gap and anisotropic shifts in the ferromagnetic resonance (FMR) resonance fields. Both results clearly show the presence of anisotropic local magnetic fields well above $T_{\mathrm{C}}$. Our findings underscore the crucial role of magnetocrystalline anisotropy in driving long-range magnetic order in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$.

The spinel compounds ${\mathrm{MnSc}}_2{X}_4$ are highly frustrated and candidate materials for vortex-like 3 q magnetic states, such as skyrmions, with propagation vectors in the [111] plane. Because of the strong magnetoelastic coupling, we could extract a refined magnetic $(H,T)$ phase diagram for ${\mathrm{MnSc}}_2{\mathrm{S}}_4$ from ultrasound and dilatometry measurements. We found a variety of magnetic phases, including the skyrmion phase, which is stable down to lowest temperatures. In comparison, we investigated ${\mathrm{MnSc}}_2{\mathrm{Se}}_4$, having a larger distance between the magnetic ${\mathrm{Mn}}^{3+}$ ions using the same methods. Unlike in ${\mathrm{MnSc}}_2{\mathrm{S}}_4$, we found no skyrmion phase and overall a lack of sharp anomalies indicative of phase transitions, neither in dilatometry nor ultrasound nor in specific heat and ac-susceptibility data. Motivated by our findings, we performed model calculations, which reproduced the experimentally observed magnetostriction and specific-heat results reasonably well.

Kagome metals have established a new arena for correlated electron physics. To date, the predominant experimental evidence centers around unconventional charge order, nematicity, and superconductivity, while magnetic fluctuations due to electronic interactions, i.e., beyond local atomic magnetism, have largely been elusive. We find the challenge of locating the appropriate parameter regime for such exotic order to center around two aspects. First, the correlations implied by low-energy orbitals have to be sufficiently large to yield a dominance of magnetic fluctuations and sufficiently weak to retain an itinerant parent state. Second, the kinematic kagome profile at the Fermi level demands an efficient mitigation of sublattice interference causing the suppression of magnetic fluctuations descending from electronic on-site repulsion. We elucidate our methodology by analyzing the potential copper-based kagome compound ${\mathrm{CsCu}}_3{\mathrm{Cl}}_5$: From ab initio design and many-body analysis, we develop a model framework of realistic Cu-based kagome materials, the simulations of which reveal unconventional magnetic order in a kagome metal.

This study establishes a comprehensive framework for the three-dimensional strain control of magnetic skyrmion strings. We integrate analytical modeling, micromagnetic simulations, and in situ Lorentz transmission electron microscopy experiments to demonstrate that externally applied strain is a powerful stimuli for manipulating three-dimensional magnetic skyrmion strings. Analytical models predict that strain induces both elongation and bidirectional tilting of skyrmion strings in bulk systems, a finding corroborated by numerical simulations. These simulations further reveal that strain drives the system from fragmented multidomain states toward unified single-domain configurations and facilitates skyrmion string rupture via bobber formation at critical strain levels. The collapse of the skyrmion lattice exhibits a temperature-dependent character, shifting from first-order to second-order behavior near the critical temperature $T_c$. Reducing sample thickness significantly increases the critical strain required for annihilation due to the suppression of tilting. Experimental validation on a ${\text{Co}}_8{\text{Zn}}_{8.5}{\text{Mn}}_{3.5}$ sample confirms strain-induced elongation and subsequent collapse into a conical phase via void cluster formation, directly implicating strain-modulated Dzyaloshinskii-Moriya interaction as the primary mechanism in this system, over magnetocrystalline anisotropy. These findings provide a mechanistic understanding of strain-mediated control in three-dimensional magnetic systems, demonstrating its feasibility for energy-efficient spintronic applications.

Interacting bosons in optical lattices directly expose quantum phases in a clean, highly controllable environment. This requires engineering systems with very low entropies, but the resulting temperature–interaction ratios $T/U$ of present experiments remain well above the domain where zero-temperature theories are expected to be reliable. The quantum-rotor approach (QRA), while analytically powerful and extremely flexible, inherits ground-state phase correlations and therefore breaks down once thermal winding of the phase field becomes significant. Here we construct a finite-temperature extension of QRA by (i) performing resummation of winding-number contributions for temperatures $k_{B}T/U\lesssim 0.2$ and (ii) developing an auxiliary-variable expansion that remains accurate toward the classical limit. The resulting closed expression for the phase correlator is inserted into the standard spherical-approximation QRA without sacrificing the method's flexibility with respect to lattice geometry and dimensionality. The approach reproduces the shrinkage of Mott lobes from $T=0$ up to $k_{B}T/U\simeq 0.2$ in quantitative agreement with theoretical predictions and with in-situ imaging experiments. This finite-T QRA thus supplies an analytic, computationally light tool for strongly correlated lattice bosons and sets the stage for amplitude-fluctuation upgrades required at higher temperatures.

Achieving structural stability and high critical temperature $\left(T_c\right)$ in hydrides under ambient conditions remains a major challenge. A feasible design strategy integrates the advantages of two material classes: (i) B-C–based clathrate superconductors, which exhibit excellent structural stability at ambient or relatively low pressures, and (ii) hydrogen-based unit, which possesses the potential for high $T_c$. Guided by this strategy, we theoretically predict a hypothetical compound ${\mathrm{NH}}_4{\mathrm{B}}_2{\mathrm{C}}_8$ by embedding hydrogenated units into a B-C clathrate framework. Using the stochastic self-consistent harmonic approximation combined with machine-learning-accelerated structural sampling, we assess the impact of anharmonicity on its superconducting properties. Anharmonic effects harden the dominant phonon modes 13–15, reducing the electron-phonon coupling constant $\lambda$ from 1.43 to 1.22 and lowering $T_{\text{c}}$ from 102 to 91 K. Furthermore, hole doping realized by ${\mathrm{NH}}_4$ vacancy engineering, which yields ${\left({\text{NH}}_4\right)}_3{\left({\text{B}}_2{\text{C}}_8\right)}_4$, is demonstrated to be ineffective in enhancing $T_c$ under anharmonic conditions. Our results highlight the synergistic role between hydrogen units and B-C frameworks in enhancing superconductivity, and underscore the importance of anharmonicity in the design of such superconductors.

Since the discovery of the Andreev reflection process at normal-metal/superconductor junctions and the corresponding Andreev bound states in superconductor/normal-metal/superconductor junctions, various multiterminal Josephson junctions have been studied to explore many exotic phases of quantum matter, where the formation of Andreev bound states in the normal region account for dissipationless supercurrent and play a central role in determining exotic properties. Recently, an intriguing aspect of the multiterminal Josephson junctions has been proposed to study the topological properties, wherein the Andreev bound states acquire topological characteristics upon tuning the phase differences of superconducting terminals. In this work, we investigate topologically nontrivial phases in four-terminal Josephson junctions based on square and graphene lattices. Additionally, we apply a gating potential that smoothly drives the Andreev bound states from a topologically nontrivial state to a topologically trivial state. Furthermore, we observe that the gating potential in our setup produces similar physics of the topological Andreev bound states of the double (single) quantum-dot multiterminal Josephson junctions when the gating potential is small (large) compared to the superconducting energy gap.

The theoretical investigation of high-entropy alloys (HEAs) from 0 K to melting temperature is proposed through a workflow combining density functional theory (DFT), Monte Carlo simulations, and machine learning. This workflow provides accurate predictions for HEA phases and enables a detailed characterization of defects in HEAs. This study enables the incorporation of anharmonic vibrational free energy in the understanding of point defects in HEAs, providing a useful approach for understanding the complex energy landscape of HEAs. The chosen HEA is Ti-V-Ta-W, for which thousands of DFT calculations over a wide range of compositions were conducted to design a reliable machine-learning force field. Predicted properties such as lattice parameters, elastic constants, distributions of formation energies of vacancy and interstitial defects, and anharmonic free energy of monovacancy formation have been discussed. This paper opens the way for a systematic investigation of high-temperature HEA properties with DFT accuracy. The presented methodology can support systematic investigation of high-temperature HEA properties with DFT-level accuracy.

We propose a novel renormalization-group (RG) method for non-mean-field models of spin glasses, which leads to the emergence of a novel order parameter. Unlike previous approaches where the RG procedure is based on a priori notions on the system, our analysis follows a minimality principle, where no a priori assumption is made. We apply our approach to a spin-glass model built on a hierarchical lattice. In the RG decimation procedure, a novel order parameter spontaneously emerges from the system symmetries, and self-similarity features of the RG transformation only. This order parameter is the projection of the spin configurations on the ground state of the system. Kadanoff's majority rule for ferromagnetic systems is replaced by a more complex scheme, which involves such a novel order parameter. The ground state thus acts as a pattern which translates spin configurations from one length scale to another. The rescaling RG procedure is based on a minimal, information-theory approach and, combined with the decimation, it yields a complete RG transformation. Below the upper critical dimension, the predictions for the critical exponent $\nu$, which describes the critical divergence of the correlation length, are in excellent agreement with numerical simulations from both this and previous studies. Overall, this study opens new avenues in the understanding of the critical ordering of realistic spin glasses, and it can be applied to spin-glass models on a cubic lattice and nearest-neighbor couplings which directly model spin-glass materials, such as AuFe, CuMn, and other magnetic alloys.

The standard understanding of topological protection from band theory is that a system's topology cannot change without first closing the bulk band gap. However, in Floquet systems, this typical definition of topological protection is one step removed from the experimentally accessible system parameters, as the relationship between the disorder in a system's instantaneous Hamiltonian and its Floquet Hamiltonian that defines its topology is not straightforward. Here, we demonstrate that the spectral localizer framework for classifying material topology can be applied to Floquet systems using solely the Floquet Hamiltonian and prove that its associated measure of topological protection can be understood in terms of the disorder across the system's instantaneous Hamiltonians. As such, we have derived a quantitative bound on a Floquet system's topological protection in terms of the instantaneous system. Moreover, we show the utility of these bounds in both ordinary and anomalous Floquet Chern insulators.

Spin waves propagating in magnetic materials exhibit nonlinear behavior at large amplitudes due to the competition between excitation and relaxation, providing an attractive platform for exploring nonlinear wave dynamics. In particular, spin waves with a nonzero wave number that carry momentum undergo nonlinear relaxation and experience wave number modulation in the nonlinear regime. This nonlinearity has been observed experimentally—for example, in S. R. Lake et al., Phys. Rev. Appl. 17, 034010 (2022)—but a quantitative comparison with theory has not yet been carried out. Here, we image nonlinear spin-wave propagation in two yttrium iron garnet thin films with distinct spin-wave decay rates using a wide-field quantum diamond microscope. We obtain quantitative distributions of spin-wave amplitude and phase as a function of the excitation microwave strength. As a result, we observe a threshold in the spin-wave amplitude beyond which nonlinear effects become evident and confirm that this threshold is consistent with theoretical predictions based on four-magnon scattering for both samples. Moreover, as the amplitude of the spin waves increases, we observe modulation of the wave number across the field of view. We attribute this modulation primarily to a reduction in the saturation magnetization caused by incoherent spin waves generated by multimagnon scattering. Our quantitative measurements provide a pathway for visualizing nonlinear spin-wave dynamics and are crucial for deepening our understanding of the underlying mechanisms.