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.

We apply the correlation matrix Hamiltonian reconstruction technique to the two-dimensional Gutzwiller-projected Fermi sea and $\pi$-flux states on finite-sized square and triangular lattices. Our results indicate no spin Hamiltonian with simple local interaction terms stabilizes such states for finite system sizes. We develop a quantitative assessment of the importance of local interactions to the stabilization of these liquid states. Lastly, we systematically assess arguments for the origin of local terms driving a Gutzwiller-projected ground state.

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.

Transition-metal dipnictides $R{X}_2$ ($R=\mathrm{Nb}$ or Ta and $X=\mathrm{P}$, Sb, or As) represent a key class of topological semimetals that exhibit rich quantum transport phenomena owing to their nontrivial band topology. However, their thermal transport mechanisms remain poorly understood. Here, using first-principles calculations combined with the Boltzmann transport equation, we systematically investigate thermal transport in the topological semimetal ${\mathrm{NbP}}_2$, which hosts nodal lines in the absence of spin-orbit coupling. In contrast to common metals, phonons are found to dominate heat transport in ${\mathrm{NbP}}_2$, which is largely due to exceptionally weak phonon-electron scattering arising from the low electronic density of states near the Fermi level associated with its topological electronic states. More intriguingly, we observe a pronounced upward deviation from the Wiedemann-Franz law, with the Lorenz number ($L_{\mathrm{e}}$) exceeding the Sommerfeld value ($L_0$) by up to 40%. Band-resolved analysis reveals that this deviation originates from nearly perfect electron-hole compensation dictated by the nontrivial band structure, which facilitates strong bipolar diffusive transport. Furthermore, we find that the degree of electron-hole compensation, and consequently the deviation of $L_{\mathrm{e}}$ from $L_0$, is highly sensitive to the chemical-potential position. Our work provides important insights into unconventional thermal transport in topological semimetals and underscores the role of band topology in governing the interplay between charge and heat transport.

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.

$\eta$-pairing symmetry provides exact singlet-pair eigenstates of the Hubbard model but is broken by interlayer density interactions. Here we construct an interlayer spin-triplet pair operator in a spinful multilayer extended Hubbard model. A restricted spectrum-generating algebra yields a tower of exact eigenstates exhibiting off-diagonal long-range order. The double commutator shows that this tower exists for bilayer and trilayer systems with finite interlayer interaction, but the construction fails for four or more layers. We also examine the spin-one structure, the trilayer case, and the relation to on-site singlet $\eta$ pairs. Exact diagonalization locates the tower within the many-body spectrum and gives its entanglement entropy. A calculation on stacked T-shaped clusters finds constant fidelity for three layers and a decrease from unity for four layers.

Using auxiliary-field quantum Monte Carlo simulations, we study the zero-temperature attractive Hubbard model on the kagome lattice at various relevant electronic fillings. The low-energy physics at $2/3$-density is influenced by the Dirac point at the Fermi energy, wherein we unveil a superfluid transition at a critical attractive interaction $U_c/t=-4.58\left(3\right)$, which belongs to the chiral-XY universality class. This U(1) symmetry-breaking is not accompanied by charge order, even for substantially large interaction strengths, in a regime where a description in terms of hardcore bosons becomes increasingly suitable. An investigation of the latter shows that charge ordering at $1/3$-filling only occurs at interaction strengths much larger than those corresponding to the mapping to the original fermionic model. Additionally, for densities exhibiting van Hove singularities in the noninteracting density of states, our results show that any attractive interaction gives rise to superfluidity, yet again without charge ordering, contrary to recent studies employing mean-field theory.

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.

Quantum-critical many-body states host universal correlations extending across all length scales. Whether these critical correlations merely characterize quantum-critical matter or can actively generate interactions that organize collective order has remained an open question. Here, we establish the concept of quantum-critical mediation, in which a quantum-critical state functions as an active mediator that dynamically generates effective interactions between otherwise weakly coupled degrees of freedom. We demonstrate this mechanism experimentally in a radical-Ni quantum magnet, where strongly coupled spin-1/2 chains realize a Tomonaga-Luttinger liquid (TLL) and anisotropic spin-1 moments remain as low-energy degrees of freedom. Combining thermodynamic measurements, quantum Monte Carlo simulations, bosonization, and conformal field theory, we show that critical TLL correlations generate an emergent two-dimensional interaction network that stabilizes long-range antiferromagnetic order. Our results reveal another function of quantum-critical matter—not merely as a phase exhibiting universal correlations, but as an organizing element that creates interactions and drives collective order. This work establishes quantum-critical mediation as a general organizing principle for emergent collective phenomena and provides a framework for engineering collective states from critical many-body correlations.

Entanglement asymmetry provides a quantitative measure of symmetry breaking in many-body quantum states. Focusing on inhomogeneous $\mathrm{U}\left(1\right)$ charges, such as dipole and multipole moments, we show that the typical asymmetry is bounded by a universal fraction of its maximal value. Multipole charges naturally arise in systems with Hilbert-space fragmentation, where the dynamics splits into exponentially many disconnected sectors. Using the commutant algebra formalism, we generalize entanglement asymmetry to account for fragmentation. While the asymmetry grows logarithmically for conventional symmetries, it can scale extensively in fragmented systems and distinguish classical from quantum fragmentation. We derive general upper bounds for the asymmetry and identify states that saturate them. To study the typical behavior of the asymmetry, we consider the ensemble of random matrix product states. By identifying the bond dimension with an effective time parameter, we qualitatively reproduce recent results on asymmetry dynamics in random quantum circuits, suggesting a universal behavior for the asymmetry of $\mathrm{U}\left(1\right)$ charges in local ergodic systems.