Discrete time crystals (DTCs) have emerged as a significant phase of matter for out-of-equilibrium many-body systems. In this work, we study how random long-range interactions contribute to the stability of the DTC phase. Generally, a stable DTC phase is believed to be realized in disordered systems with short-range interactions. Here, we explore a periodically driven quantum Sherrington-Kirkpatrick (SK) model of Ising spin-glass in which all spins are coupled to each other randomly. We investigate the possibilities of the DTC phase in the SK model within three different driving protocols and found that the quantum SK model exhibits a robust DTC phase, although systems with uniform long-range interactions can exhibit only a prethermal DTC phase. Further, we demonstrate that disorder in the local $XY$ term or transverse field is crucial for stabilizing a broad DTC phase, despite random couplings in the SK model. Our analysis shows that the stability of the DTC phase is determined by the nonergodic nature of the Floquet eigenstates and spectral pairing of even and odd spin-flip parity eigenstates of the Floquet spectrum.

High-temperature and high-magnetic-field-induced reentrant superconductivity has been discovered in the infinite-layer nickelate ${\mathrm{Sm}}_{1-x-y}{\text{Eu}}_x{\text{Ca}}_y{\text{NiO}}_2$ (SECNO). Infinite-layer nickelates are the closest known analogs of high-$T_c$ cuprate superconductors, yet they host distinct magnetic ground states. Using low-energy muon spin relaxation and polarized neutron reflectometry, we reveal the magnetic order in SECNO. Magnetic freezing occurs at a significantly higher temperature than in other nickelate compounds, and a net magnetization of $55\pm 10\mathrm{kA}{\mathrm{m}}^{-1}$ emerges and remains largely unchanged across the superconducting transition. The magnitude and temperature dependence of this net magnetization are inconsistent with a paramagnetic response, and instead point towards an as-yet unidentified magnetic ordering of Eu moments. These observations suggest a close connection between the magnetic state and the unique superconducting physics exhibited by SECNO, providing a potential mechanism for Jaccarino-Peter screening in high magnetic fields.

We develop a molecular dynamics framework to compute the mode-resolved phonon spectral density from classical correlations of an annihilation-like phonon variable. For harmonic oscillators, classical molecular dynamics exactly reproduces the corresponding quantum Kubo-transformed correlator, providing the basis for extension to anharmonic systems. Using PbTe as a benchmark and ${\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{I}}_6{\mathrm{Cl}}_3$ as a strongly anharmonic test case, we show that the method captures both quasiparticle and non-Lorentzian spectra beyond perturbative quasiparticle theory, while yielding thermal conductivity in good agreement with experiment. This framework provides a classical molecular dynamics route to mode-resolved phonon spectral densities for spectral Wigner heat transport in strongly anharmonic solids above their Debye temperatures.

Indirect long-range interactions between localized magnetic moments in metals are mediated by itinerant electrons. In insulators and semiconductors, such interactions cannot be mediated by itinerant electrons; however, delocalized electrons in the valence band may provide such a medium. Nevertheless, the existence of magnetically ordered insulators, for instance, metal oxides, is therefore an everlasting source for proposals of various mechanisms that may support the order. Here, phonon-mediated interactions between localized magnetic moments are considered as a mechanism that can provide quantifiable symmetric and antisymmetric anisotropic spin-spin interactions. It is demonstrated that while a symmetric anisotropic interaction exists for all types of phonons, the existence of antisymmetric anisotropic interactions requires broken inversion symmetry. The latter mechanism may explain the weak ferromagnetic order observed in chiral compounds, e.g., CuO and CoO. Furthermore, the interaction is nearly independent of temperature at low temperatures, while it approaches linear growth at high temperatures. Spatially, the interactions have an oscillatory power-law decay with the interatomic distance.

Multisublattice antiferromagnets with complex crystallographic structures can give rise to nontrivial spin ordering due to competing exchange couplings within and between different subsystems of magnetic ions. In nickel orthoborate ${\mathrm{Ni}}_3{\left({\mathrm{BO}}_3\right)}_2$ there are two distinct subsystems of the ${\mathrm{Ni}}^{2+}$ ions $(S=1)$ that are antiferromagnetically ordered below $T_N=46\mathrm{K}$, forming complex spin ordering and multiple branches of magnons. We report a comprehensive experimental study of single-crystal spin dynamics using polarized Raman scattering and infrared absorption spectroscopy. A rich multibranch spin-wave spectrum covering a broad energy range was observed via one-magnon scattering. Additionally, we detected the formation of a complex-shape two-magnon band in the range of $60–200{\mathrm{cm}}^{-1}$. These findings were supported by calculations using linear spin-wave theory, which allowed us to describe the shape of the two-magnon band and propose an exchange structure for the antiferromagnetic nickel orthoborate ${\mathrm{Ni}}_3{\left({\mathrm{BO}}_3\right)}_2$ compatible with experimental observations.

The symmetry of the superconducting gap is related to the symmetry of the crystal structure. In unconventional superconductors, big changes in the critical temperature, critical field, or even the gap structure can happen even for small perturbations of the lattice. In this paper, we use microstructuring to study aluminum-free micro crystals of ${\mathrm{UBe}}_{13}$ which are expected to be closer to a “perfect” material than previously studied aluminum-grown single crystals. We compare the effect of minuscule imperfections on the value of the critical temperature and critical field, which, in the case of ${\mathrm{UBe}}_{13}$, has drastic effects, supporting its unconventional nature. We conjecture that this likely arises from the oxidation state of uranium, which is sensitive to its crystallographic environment. Our findings suggest that uranium-based materials provide not only an excellent reservoir of unconventional phenomena, but also a way to identify the gap symmetry of unconventional superconductors.

MnAs and CrAs are widely studied systems owing to their unconventional magnetostructural phase transitions and the associated magnetic, spintronic, and superconducting properties. In this work, we investigated the magnetostructural properties of ${\text{Mn}}_{(1-x)}{\text{Cr}}_x\text{As}$ compounds, which span from the hexagonal collinear ferromagnet (MnAs) to the orthorhombic noncollinear spin-spiral (CrAs). First-principles density functional theory calculations were employed for ${\text{Mn}}_{(1-x)}{\text{Cr}}_x\text{As}$ to explore the ground state crystal and magnetic structures, magnetism, spin-spiral propagation vectors, symmetric and antisymmetric exchange interactions, and magneto-optical properties such as x-ray magnetic circular dichroism, Kerr, and Faraday effects. Monte Carlo simulations were employed to estimate the magnetic transition temperatures and magnetic entropy change with respect to the applied magnetic field. The calculated equilibrium lattice parameters, magnetic moments, and transition temperatures showed good agreement with available experimental data, reinforcing the validity of our theoretical approach. Analysis of the symmetric and antisymmetric exchange interactions provide deeper insight into the noncollinear magnetic ordering in CrAs and the substituted systems. In the noncollinear magnetic configurations, the first two nearest-neighbor (NN) and next two NN symmetric Heisenberg exchange interactions are of opposite sign with comparable magnitude inducing a magnetic frustration and exhibiting a long-range oscillatory behavior implying the presence of Ruderman-Kittel-Kasuya-Yosida interactions. Understanding the intricate role of competing magnetic exchange interactions and their coupling with the crystal structure is crucial for describing the emergence of helimagnetic ordering in ${\text{Mn}}_{(1-x)}{\text{Cr}}_x\text{As}$.

We study the effect of electric current and magnetic field on the dynamics of chirality in a helimagnet with a strong easy-plane anisotropy. Using a continuum theory derived for a quasi-one-dimensional frustrated ferromagnet close to the Lifshitz point, we show that a domain wall connecting domains with opposite chiralities can be driven by the current via the dissipative (nonadiabatic) component of the spin-transfer torque. Further, it is demonstrated that the adiabatic part of the torque in the presence of a magnetic field breaks the symmetry of the effective magnetic potential energy with respect to the chirality. We show that the leading symmetry-breaking term arises in the third order in the magnetization gradient, and derive the conditions for chirality switching. Our conclusions are supported by numerical spin-lattice simulations.

Unlike conventional approaches where topological order is statically fixed, we demonstrate that biaxial strain can independently modulate topological order and functional responses in a Tc-adsorbed penta-hexa-silicene monolayer. Combining first-principles calculations and tight-binding models, we establish a continuous topological pathway $C=+1\to 0\to -1$ driven purely by strain, with the intermediate $C=0$ state being a gapped insulator rather than a gapless critical point. This evolution is governed by momentum-space orbital-selective engineering, which selectively reconfigures wave functions to reshape the global Berry curvature distribution. Crucially, we reveal a fundamental dichotomy: topology originates from the global phase distribution of orbital hybridization, while piezoelectric functionality arises from its local strength. This enables the coexistence of nontrivial Chern insulating states with giant electromechanical responses ($d_{11}\approx 11$ pm/V, three times that of ${\text{MoS}}_2$), establishing a paradigm for transforming static functional materials into dynamically tunable quantum platforms.

${\mathrm{Cr}}_{1/4-\delta }{\mathrm{NbSe}}_2$ $(\delta =0.065)$ is a triangular lattice magnet in which magnetic ${\mathrm{Cr}}^{3+}$ ions are intercalated to form $2a\times 2a$ triangular superlattices between ${\mathrm{NbSe}}_2$ van der Waals layers stacked along the $c$ axis. By unpolarized and polarized neutron scattering experiments, we have revealed that the magnetic ground state of this system is a ${120}^{\circ }$-type antiferromagnetic order characterized by the magnetic propagation wave vector of $q=(\frac{1}{3},\frac{1}{3},0)$. We also performed inelastic neutron scattering measurements using coaligned single crystals, and we determined dispersion relations of magnetic excitations at low temperatures. Comparing the observed spectra with calculations based on the linear spin-wave theory, we revealed that the out-of-plane ferromagnetic interaction is fairly strong as compared to the in-plane nearest-neighbor antiferromagnetic interaction. Although the crystal structure of this system is composed of two-dimensional van der Waals layers, the magnetic order has a three-dimensional character, which would be attributed to long-range magnetic interactions mediated by conduction electrons.

We show that the Bose-Einstein condensate (BEC) of magnons in superfluid ${}^3\mathrm{He}$-B in the form of a homogeneously precessing domain can be used as a new type of tuned resonant quantum amplifier. The underlying physical principle of the resonant amplification is the violation of the U(1) (calibration) symmetry in this coherent magnonic system which opens an energy gap in the spectrum of collective excitations. We demonstrate that the magnon resonance amplifier operates in two reference frames: (i) in the rotating frame without thermal bath, where the signal is detected and (ii) in the laboratory frame, where the signal is measured, as a consequence of the Cooper pairs decay. As the thermal bath is not present in the rotating frame of reference, the amplifier may achieve an extremely low effective noise temperature. The proposed principle of the quantum amplification can be tested in other physical systems, where the BEC of magnons has been observed and these systems exhibit the violation of U(1) symmetry.

Two-dimensional topological insulators (2D TIs) are commonly realized either through intrinsic band-gap inversion within a single material or through interfacial band-offset inversion in narrowly tuned heterostructures. Here we demonstrate, based on first-principles calculations, that these two mechanisms can be unified within a single heteroepitaxial platform. We show that monolayer ${\mathrm{GaAs}}_{1-x}{\mathrm{Bi}}_x$ grown on GaSb(111) hosts a robust 2D TI phase for all alloy compositions $0\le x\le 1$, with a large topological gap ranging from ∼90 to 240 meV. Layer- and orbital-resolved band analyses show a smooth evolution from interfacial band-offset inversion at low Bi concentration to intrinsic band-gap inversion at high Bi concentration. This evolution is captured by a two-band Dirac (Bernevig-Hughes-Zhang  model-type) Hamiltonian with a continuously inverted Dirac mass, placing all band-alignment regimes within the same topological universality class. Our results establish a realistic III–V semiconductor platform for integrating large-gap 2D TIs into wafer-scale device architectures.

We theoretically predict the interaction between polaritonic excitations arising from the coupling of a cavity photon mode with bound to continuum intersubband transitions in a doped quantum well. The resulting exciton bound by photon exchange, recently demonstrated experimentally, exhibits a binding energy that can be continuously tuned by varying the cavity frequency. We show that polariton-polariton interactions, originating from both Coulomb interactions and Pauli blocking, can be dramatically enhanced by reducing the exciton binding energy, thereby increasing the effective Bohr radius along the growth (vertical) direction. This regime is reminiscent of Rydberg atoms, where weak binding leads to strong quantum interactions. Our predictions indicate that this physics can give rise to giant quantum optical nonlinearities in the mid and far infrared, a spectral region that remains largely unexplored in quantum optics and offers exciting opportunities for both fundamental studies and applications.

We investigate the microwave-power dependence of magnon-photon coupling in a yttrium iron garnet-sphere/split-ring resonator hybrid system at room temperature and demonstrate that nonlinear spin-wave interactions suppress the coupling through power-induced dissipation of magnetostatic modes. At low microwave power, the modes exhibit pronounced level repulsion, evidencing strong coupling to the microwave field. As the power increases, however, magnon-linewidth broadening progressively weakens the coupling and ultimately suppresses it entirely below a threshold external magnetic field. We show that this behavior originates from Suhl's first-order instability: Magnetostatic modes, which couple to the resonator, parametrically excite two counterpropagating magnons at half their frequency, causing modes below the threshold external magnetic field to vanish. In contrast, magnon modes above the threshold field remain robust even at high power, as the instability criterion is not satisfied in that regime. These results reveal a well-defined nonlinear boundary for magnon-photon coupled systems and highlight a favorable regime for exploiting nonlinear magnonics for frequency conversion, switching, and other functional magnonic devices.

The nitrogen-vacancy (NV) center in diamond is the prototype quantum defect that enables a variety of diamond-based quantum technologies. However, charge-state instability and spectral diffusion, often induced by substitutional nitrogen impurities (${\mathrm{N}}_{\mathrm{C}}$), remain key challenges for device performance. Here, we employ first-principles density functional theory calculations to quantitatively investigate nonradiative carrier capture processes mediated by multiphonon emission at both the NV center and the ${\mathrm{N}}_{\mathrm{C}}$ impurity. For relevant cases, we also compute the rates of radiative and thermal emission processes. For ${\mathrm{N}}_{\mathrm{C}}^0\to {\mathrm{N}}_{\mathrm{C}}^{-}$, we obtain an electron capture coefficient of $2.2\times {10}^{-8}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at 300 K. Both the magnitude and the temperature dependence are in excellent agreement with experimentally measured capture cross sections. Electron capture at ${\mathrm{N}}_{\mathrm{C}}^{+}$ is even faster, with a capture coefficient of $1.0\times {10}^{-4}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at 300 K. For the NV center, we find that carrier capture rates involving only the ground states of ${\mathrm{NV}}^0$ and ${\mathrm{NV}}^{-}$ are negligibly slow. However, capture into the excited states (${\mathrm{NV}}^{0*}$ and ${\mathrm{NV}}^{-*}$) is significantly faster. In particular, the capture coefficient for the hole capture process ${\mathrm{NV}}^{-}\to {\mathrm{NV}}^{0*}$ is as large as $1.8\times {10}^{-7}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ and largely temperature independent. Hole capture at ${\mathrm{NV}}^{-}$ will thus occur via nonradiative capture into an excited state of ${\mathrm{NV}}^0$ followed by fast radiative decay to the ${\mathrm{NV}}^0$ ground state. Similarly, electron capture at ${\mathrm{NV}}^0$ will occur via the ${\mathrm{NV}}^0\to {\mathrm{NV}}^{-*}\to {\mathrm{NV}}^{-}$ pathway, but with a lower nonradiative capture coefficient ($2.1\times {10}^{-9}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at 300 K). Our calculated capture coefficients and rates provide essential information for analyzing charge-state dynamics.

Spin-torque vortex oscillators provide a model system for the nonlinear dynamics of a confined magnetic texture. Their motion is commonly described by the Thiele equation, but its standard form keeps the gyrovector and damping tensor fixed at their rigid-vortex values and becomes inaccurate at large gyration amplitudes. We introduce a data-driven Thiele equation approach that extracts effective, position-dependent Thiele coefficients from a single current-ramp micromagnetic simulation by interpolating the magnetization in vortex-core-position space. The extracted maps reveal a weak increase of the gyrovector magnitude and a pronounced separation of the radial and azimuthal dissipation as the orbit expands, providing quantitative signatures of confinement- and motion-induced vortex deformation. Because the gyrotropic, dissipative, conservative, and spin-transfer contributions retain their usual Thiele structure, the resulting description remains physically interpretable rather than acting as a black-box surrogate. Incorporating these state-dependent coefficients into the equation reproduces the nonlinear stable-orbit dynamics and accurately predicts the response to time-varying currents, whereas a conventional constant-coefficient description predicts vortex expulsion. The framework therefore provides a systematic route for deriving effective collective-coordinate dynamics from full micromagnetic states with high computational efficiency.

Crystal-field symmetry restricts the ground-state Kramers doublet of ${\mathrm{ErBr}}_3$ to one of two classes. We show that the compressed octahedral environment selects the class with $\langle {\psi }_{\pm }\left|J^{\pm }\right|{\psi }_{\mp }\rangle =0$, suppressing the lowest-order $J^{\pm }$-mediated exchange. Thermodynamic measurements reveal two zero-field anomalies at 0.375 and 0.200 K. Under an in-plane magnetic field, the thermodynamic response separates into a phase boundary and a broader crossover line. Inelastic neutron scattering measurements at 2 K reveal no well-defined low-energy dispersive magnetic modes. These results connect the ground-state symmetry with the field-dependent thermodynamic response of ${\mathrm{ErBr}}_3$, providing a microscopic starting point for understanding its low-energy magnetic behavior.

The Ni-Co-V medium-entropy alloy exhibits exceptional strength and ductility, often attributed to its pronounced chemical short-range order (CSRO) driven by Ni-V and Co-V affinity. Yet how this tunable CSRO governs stacking-fault energetics and dislocation motion remains unresolved. Using atomistic simulations based on our first-principles-trained interatomic potential, we show that as CSRO intensifies, the average intrinsic stacking-fault energy increases from 25 to $95\text{mJ}{\text{m}}^{-2}$ and the mean critical resolved shear stress rises from $340.9\pm 23.0$ to $521.3\pm 20.9\text{MPa}$. Dislocation analysis reveals reduced partial separation and enhanced resistance to partial-dislocation glide with increasing order. Introducing Ni-V- and Co-V-rich CSRO clusters along the glide plane induces bowing, kinking, and transient pinning, demonstrating spatially heterogeneous chemical strengthening. These results quantitatively link CSRO to stacking-fault-mediated plasticity and establish tunable strength-ductility through controlled local chemical order in Ni-Co-V systems.

Quantum many-body systems in cavities combine the rich physics of condensed matter systems or quantum chemistry with strong coupling to the surrounding electromagnetic field. In these systems, large Hilbert spaces, many-body interactions, and strong system-environment coupling are all fundamental, posing a significant barrier for established methods in quantum optics and condensed matter physics. Here we propose a novel method based on a combination of the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy [M. Bonitz, Quantum Kinetic Theory (Springer International Publishing, Cham, 2016)] and the Hierarchical Equations of Motion (HEOM) [Y. Tanimura, Phys. Rev. A 41, 6676 (1990)] to achieve a rigorous description of open many-body systems in contact with structured photonic and phononic baths. We rationalize that this stacked hierarchy accounts for spin squeezing and superradiant emission despite its applicability to arbitrarily many emitters. The potential of BBGKY-HEOM is then demonstrated for many-body electronic systems embedded in host materials (e.g., molecules in organic crystals). We show that the impact of phononic coupling and charge noise can be as relevant as electronic correlation. Our work establishes an accessible, yet rigorous, route between condensed matter and quantum optics, fostering the growth of a new domain at their interface.