The interplay between magnetism and superconductivity is one of the central topics of condensed matter physics, which has recently been put into new light by the discovery of altermagnets. Here, we study this interplay from a fundamental symmetry perspective using irreducible co-representations of the altermagnetic spin-point groups. We construct and tabulate all symmetry-allowed pairing functions for altermagnets, which uncovers numerous exotic pairing states. We focus on three of them, namely, (i) a nonunitary altermagnetic superconductor with different spatial anisotropies for the spin-up and spin-down condensates, (ii) a half-and-half metal-superconductor where only electrons with one of the two spin components form Cooper pairs, and (iii) a spin chiral superconductor with spin-polarized chiral edge states. Interestingly, the first of these three superconductors exhibits an unusual fractional ac Josephson current for only one of the two spin polarizations, even though the two condensates are symmetry related. We present phenomenological Ginzburg-Landau theories for these unconventional superconductors and show that they correspond to stable minima of the free energies. We examine their topological properties, study the effects of small spin-orbit coupling, consider possible material examples, and investigate their topological responses.

Interacting spin chains and ladders are known to support a plethora of quantum phases with complex ground-state phase diagrams. In this work, we study a large family of such models and determine precise, explicit conditions under which an exact dimer state is guaranteed to be their ground state. These general conditions are validated for various generalizations of the Majumdar-Ghosh model using exact diagonalization. Our results provide exact reference points in the phase diagrams of a wide class of spin chains and ladders, including those with anisotropic and arbitrary-range interactions.

We obtain an exact expression for the conductivity of a non-Galilean-invariant Fermi liquid with impurities by solving the kinetic equation with both screened Coulomb and $z=3$ Pomeranchuk critical interactions. While consistent with previous asymptotic results, our solution shows that electron-electron interactions enter the conductivity solely via the quasiparticle scattering time, ${\tau }_{\mathrm{ee}}$. Accordingly, the crossovers between the collisionless and hydrodynamic regimes occur when $1/{\tau }_{\mathrm{ee}}$ becomes comparable to the larger of the impurity scattering rate and the probe frequency, $\mathrm{\Omega }$. Importantly, this crossover is governed by the quasiparticle scattering rate, rather than by a suppressed effective current-relaxation rate. The exact solution also shows that the electron-electron correction to the $\mathrm{dc}$ conductivity remains parametrically smaller than the residual conductivity throughout the Fermi-liquid regime. For the optical conductivity, our solution also provides access to the hydrodynamic regime, $\mathrm{\Omega }\ll 1/{\tau }_{\mathrm{ee}}$, which is inaccessible within perturbation theory. Near a $z=3$ Pomeranchuk quantum critical point, consistency between the kinetic equation and Kubo approaches requires proper inclusion of mass renormalization within the Eliashberg approximation, which also ensures that the crossover between the collisionless and hydrodynamic regimes in the optical conductivity occurs at the Planckian scale $\mathrm{\Omega }\sim T$.

We derive a discrete spectral representation of the single-particle self-energy using a discrete evaluation of Kugler's symmetric improved estimator. Our construction can be used on both the real and the complex (Matsubara) frequency axis. It is guaranteed to remain causal at the numerical level, in contrast to standard approaches that may generate unphysical negative spectral weight or require additional broadening. Our representation can be used for any Hamiltonian; here we apply it to quantum impurity models and in dynamical mean-field theory. The latter is formulated with a discrete hybridization function throughout its self-consistency loop. In both cases and across various numerical methods, we obtain significantly improved accuracy for a range of impurity properties.

${\mathrm{Ca}}_2\mathrm{N}$, a prototypical electride with intrinsic interstitial anionic electrons (IAEs), exhibits pressure-induced electronic phase transitions. Previous studies have revealed a pressure-induced metal-semiconductor transition in ${\mathrm{Ca}}_2\mathrm{N}$ at relatively low pressures; however, the evolution of its crystal structure and the role of interstitial electrons under extended compression remain unclear. Here, we combine first-principles calculations with crystal structure prediction to investigate the structural and electronic evolution of ${\mathrm{Ca}}_2\mathrm{N}$ up to 120 GPa. We identify six stable high-pressure phases, including $Fd\text{−}3m$, $I\text{−}42d$, $P2$, $Fm\text{−}3m$, $R\text{−}3m\text{−}\mathrm{II}$ and $I4/mmm$ for ${\mathrm{Ca}}_2\mathrm{N}$. Analysis of the pressure-dependent evolution of IAEs reveals a nonmonotonic electronic transition from metal to semiconductor and back to metal. Upon compression, extended interstitial electron states gradually transform into localized zero-dimensional states, resulting in electron confinement and gap opening. At higher pressures, the reduced interstitial volume promotes hybridization between interstitial electrons and Ca-$d$ states, leading to reentrant metallization. These results establish the high-pressure structural and electronic phase diagram of ${\mathrm{Ca}}_2\mathrm{N}$ and provide a microscopic mechanism linking interstitial electron behavior to electronic transitions in electrides, advancing understanding of pressure-driven phenomena in these materials.

$\mathrm{CH}{\left(\mathrm{N}{\mathrm{H}}_2\right)}_2\mathrm{PbB}{\mathrm{r}}_3 \left(\mathrm{FAPbB}{\mathrm{r}}_3\right)$ is a semiconducting material with the perovskite structure which has generated intense topical interest due to its potential applications in optoelectronic and spintronic devices. Its functional properties are related in part, at least, to a phenomenologically rich sequence of structural instabilities driven by octahedral tilting and dynamic effects of the $\mathrm{F}{\mathrm{A}}^{+}$ cations. Measurements of elastic, anelastic, and dielectric properties, linear thermal expansion, and heat capacity have been used to provide an unambiguous description of the full sequence of transitions. The octahedral tilting transitions at ∼264 and ∼183 K conform to 246 and close to 26 (tricritical) Landau potentials. First-order isosymmetric transitions driven by abrupt changes in $\mathrm{F}{\mathrm{A}}^{+}$ configurations occur at ∼161, 152, 145, and 121 K during cooling and at ∼162, 152, and 122 K during heating. A succession of further loss peaks below 100 K, relating primarily to dynamics of the $\mathrm{F}{\mathrm{A}}^{+}$ cations, reveals thermally activated relaxations with a spread of relaxation times and activation energies in the range ∼0.01–0.15 eV. Acoustic loss in the temperature interval ∼180–230 K indicates that ferroelastic domain walls in the stability field of the tetragonal structure were mobile under the low-stress conditions that apply during measurements by resonant ultrasound spectroscopy, with likely pinning by Br vacancies below ∼210 K. Overall patterns of hysteresis, particularly in dielectric loss behavior in the temperature interval ∼250–350 K, point to a thermal history dependence of the configurations of the $\mathrm{F}{\mathrm{A}}^{+}$ cations. The diversity of possible interactions of $\mathrm{F}{\mathrm{A}}^{+}$ cations with domain walls, antiphase boundaries and the perovskite framework has the potential to lead to polar or optoelectronic properties localized specifically within the domain walls.

The ruby lattice has been the subject of much interest recently due to its realization in Rydberg atom arrays, where its rich variety of frustrated interactions gives rise to topologically ordered quantum spin liquids. Similarly, numerical studies of ruby-lattice spin models, with both isotropic and anisotropic interactions, have provided evidence of gapped and gapless spin-liquid ground states with different low-energy gauge structures. Motivated by these findings, we perform a projective symmetry group (PSG) classification of U(1) and ${\mathbb{Z}}_2$ fermionic spinon mean-field theories—respecting space-group and time-reversal symmetries—for $S=1/2$ spins. We obtain a total of 50 U(1) and 64 ${\mathbb{Z}}_2$ PSGs, and upon restricting their realization via mean-field Ansätze with up to second-nearest-neighbor singlet amplitudes (relevant to the models studied here), only 8 U(1) and 18 ${\mathbb{Z}}_2$ distinct states are obtained. We present the singlet fields for all Ansätze up to third-nearest-neighboring bonds and discuss their spinon dispersions as well as their dynamical spin structure factors. Building on this information, we also obtain the phase diagram of the Heisenberg model in the presence of first-$\left(J_1\right)$, second-$\left(J_1^{\prime }\right)$, and third-$\left(J_2\right)$ neighbor antiferromagnetic couplings within a self-consistent mean-field approximation.

Supersolidity, combining superfluid and crystalline orders, has been realized in dipolar Bose-Einstein condensates by tuning interatomic interactions. Here, we show that supersolidity can also emerge from mode coupling at a superfluid-solid interface, without modifying bulk interactions and for a broad class of superfluids. Using an analytical and numerical treatment of the coupled superfluid and phonon fields, we derive the criterion for a density-modulation instability driven by interfacial coupling and dependent on dimensionality. In superfluid helium, the instability first appears at the roton mode, while in a Bose-Einstein condensate with contact interactions it can occur for a large range of wave vectors. Beyond the threshold, the ground state acquires an interfacial density modulation while the bulk remains superfluid, forming a hybrid superfluid-supersolid phase. Our results identify interfacial mode coupling as a promising route to supersolidity, enabling the simultaneous exploitation of interfacial supersolid and bulk superfluid quantum properties, as well as using the interface as a seed to nucleate bulk supersolidity.

A superconducting diode effect is shown to arise in ferromagnetic superconductors through the nonreciprocal dynamics of magnetic domain walls. Specifically, we show that current-driven dynamics of a magnetic domain wall under a certain external field can exhibit a nonreciprocal Walker breakdown, possessing two distinct direction-dependent critical currents beyond which the domain wall precesses continuously. In ferromagnetic superconductors, the constant rotation of a domain wall is shown to give rise to phase slips, opening up dissipation channels, whereby the nonreciprocal Walker breakdown is mapped to the superconducting diode effect. For the nonreciprocal Walker breakdown of a magnetic domain wall, we analytically examine its dependence on the magnetic field and the Gilbert damping and verify the theoretical results with micromagnetic simulations. We then extend the analysis to ferromagnetic superconductors by considering additional effects from the superconductivity and identify criteria for experimental conditions to realize the predicted superconducting diode effect. Our work demonstrates that topological defects, such as domain walls, in magnetic superconductors can serve as an intrinsic nanoscale platform for nonlinear nonreciprocal superconducting functionalities within a single homogeneous material, circumventing the need for complicated engineered heterostructures and thereby enabling the miniaturization of superconducting devices down to the nanometer scale that is challenging to achieve with conventional Josephson junctions.

We report bulk ultrasound measurements up to 77 T and down to 0.5 K of the field reentrant superconducting phase of the unconventional superconductor ${\mathrm{UTe}}_2$. Clear bulk signatures of superconductivity are observed in the longitudinal $c_{11}$ elastic mode for fields applied at a tilt angle of ${\theta }_{\mathrm{b}-\mathrm{c}}={30}^{\circ }$ from the $b$ axis. We confirm an upper critical field of $H_{\mathrm{c}2}\approx 65\mathrm{T}$ at 0.5 K and bulk superconductivity which survives up to $T\approx 2\mathrm{K}$ for fields above the metamagnetic transition. The $c_{11}$ mode has propagation and displacement vectors along the $a$ axis, and for fields applied at a tilt angle of ${\theta }_{\mathrm{b}-\mathrm{c}}={30}^{\circ }$, this mode is sensitive to the elasticity of the vortex lattice. The anomalies observed in $c_{11}$ are in part reminiscent of superconducting vortices pinned to lattice defects. Nonetheless, an excess attenuation, with respect to the normal state, is observed throughout the entire superconducting phase, suggesting unusual vortex dynamics and pinning in the field reentrant superconducting phase of ${\mathrm{UTe}}_2$.

Spin-band splitting is a hallmark of altermagnetism, intrinsically linked to magnetic ordering driven by electron correlations. However, recent inconsistencies in the detection of altermagnetism in strongly correlated altermagnet candidates have cast doubt on the robustness of this phenomenon and its dependence on many-body effects. Here, using density functional theory combined with dynamical mean-field theory ($\mathrm{DFT}+\mathrm{DMFT}$), we dissect the electronic origins of altermagnetism in three prototypical candidates: ${\mathrm{MnF}}_2$, MnTe, and ${\mathrm{RuO}}_2$. In ${\mathrm{MnF}}_2$, we identify pronounced local electron correlations within $\mathrm{Mn}\text{−}3d$ states and uncover a distinct Mott gap in the visible range. The strong correlations markedly localize the $\mathrm{Mn}\text{−}3d$ electrons, leading to a narrowing of the spin-resolved bandwidth and, consequently, a suppression of spin-band splitting. By contrast, MnTe provides an ideal platform for altermagnetism, exhibiting substantial local $\mathrm{Mn}\text{−}3d$ magnetic moments due to the strong correlations and pronounced spin-band splitting, enabled by robust $\mathrm{Mn}\text{−}3d–\mathrm{Te}\text{−}5p$ orbital hybridization. ${\mathrm{RuO}}_2$ manifests as a Pauli paramagnet with vanishing local moments, even in its antiferromagnetic phase. Nonetheless, it exhibits significant spin-band splitting, indicative of itinerant altermagnetic behavior. Our results reveal that both strong local electron correlations and judicious ligand selection to promote orbital hybridization are key prerequisites to realizing altermagnetism in strongly correlated systems. These insights pave the way for the rational design and discovery of other altermagnetic materials.

Color centers in wide-band-gap semiconductors are leading platforms for solid-state quantum technologies, yet a quantitative description of their vibronic structure has remained elusive due to the complexity of multiphonon processes in localized defect states. Here we present a first-principles Green's function framework based on the retarded cumulant ansatz (RCA) to describe electron-phonon interactions in spin defects; our approach goes beyond the adiabatic and lowest-order perturbation theory approximations underlying widely used approaches. Applied to the negatively charged nitrogen-vacancy $\left({\mathrm{NV}}^{-}\right)$ center in diamond within the harmonic approximation, our method reveals that multiphonon satellites persist over a 400 meV energy window even at zero temperature, driven by quantum zero-point fluctuations. We demonstrate that accurate spectral functions require mode-, momentum-, spin-, and orbital-resolved electron-phonon matrix elements sampled across the full Brillouin zone, to account for hybridized and propagating phonon channels. We find that the vibronic structure of the ${\mathrm{NV}}^{-}$ center exhibits strong spin and orbital anisotropy, with different orbitals coupling to qualitatively distinct parts of the phonon spectrum, and spin-selective coupling affecting both sideband positions and intensities.

The cubic perovskite ${\mathrm{SrFeO}}_3$ is a prototypical centrosymmetric itinerant magnet that hosts a quadruple-$\mathbf{Q}$ hedgehog-antihedgehog lattice and exhibits a complex magnetic-field–temperature phase diagram. Yet, the microscopic mechanism underlying the emergence of its versatile multiple-$\mathbf{Q}$ phases remains unresolved. Here, we reveal the field-orientation dependence of the magnetic phase diagram and establish an effective spin Hamiltonian for ${\mathrm{SrFeO}}_3$ that incorporates a cubic single-ion anisotropy together with bilinear and biquadratic interactions in momentum space, which originate from the spin-charge coupling. In addition, we observe magnetoelastic signatures of a redistribution of the ligand-hole density upon entering the forced ferromagnetic phase. These findings are consistent with an important role of electronic itinerancy associated with the formation of a ligand-hole band in stabilizing multiple-$\mathbf{Q}$ phases.

Most materials with high thermal conductivity belong to one of two classes: metals, where heat is carried predominantly by electrons, and insulators, where heat transport is dominated by the phonon contribution. Materials that combine substantial electronic thermal conductivity and lattice thermal conductivity are rare, because the mechanisms that favor electron transport typically suppress phonon transport, and vice versa. Here, we report the theoretical prediction and experimental realization of such a material, metallic $\varepsilon$-TaN. Our calculations predict a total thermal conductivity at room temperature of $273\pm 5\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ in single crystals and $145\pm 5\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ in polycrystals with $0.5\mu \mathrm{m}$ grains, with an unusually large lattice contribution (79%) for a metal. The latter value is in agreement with our local transient thermoreflectance measurements on polycrystalline samples yielding $\sim 130\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$. We show that the balanced electronic and lattice thermal conductivities of $\varepsilon$-TaN originate from a combination of large Fermi velocity and small Fermi density of states on the electron side, and large speed of sound and wide phonon gap on the lattice side.

We predict the spin thermal Hall effect in nonreciprocal magneto-optical many-body systems, in which a longitudinal radiative heat current generates a transverse accumulation of the spin angular momentum carried by thermal photons. We show that this effect and the inverse spin thermal Hall effect constitute an Onsager-Casimir reciprocal pair, thereby establishing heat and photon spin as coupled transport channels in nonreciprocal photonic systems. The second law of thermodynamics imposes fundamental bounds on the spin-heat coupling, leading to a thermal-spin figure of merit that quantifies the efficiency of radiative spin-heat conversion. Our results establish a complete thermodynamic framework for photon-spin caloritronics and lay the conceptual foundations for spin-controlled thermal radiation and nonreciprocal photonic thermal devices.

Recently “the hat” monotile was introduced into the family of aperiodic tilings and quasicrystals boasting physical properties lying at the boundary of ordered and disordered systems. Here we study the two-dimensional wave transport, transverse localization, and scaling properties of the quantum modes in a monotile quasilattice. Our system is based on reconfigurable optical lattices for cavity polaritons which provide flexible means to study wave packet dynamics, strong nonlinear phenomena, and power-driven condensation in this new type of an aperiodic tiling. We confirm the existence of localized and critical states in the monotile through direct diagonalization of the Schrödinger equation. Scaling analysis on the moments of the wave-function distribution reveals anomalous transport regimes of superdiffusive and near subdiffusive polariton transport associated with the fractal structure of the monotile Hilbert space. We propose a strategy using resonantly excited polariton fluids to verify our findings.

Interaction between different two-dimensional materials can give rise to many exotic physical phenomena that are rarely observed in intrinsic materials. Recently, several theoretical and experimental works have revealed that magnetic proximity effect between pristine graphene and magnetic substrates can lead to the emergence of quantum anomalous Hall states and quantum spin Hall states. However, interplay between correlated states in graphene-based systems and magnetic materials has seldom been studied. Here, we perform the transport measurement at ultrahigh magnetic field of twisted double bilayer graphene (TDBG) on CrOCl (COC) substrate, which is an antiferromagnetic material. Instead of a magnetic-exchange effect on graphene, we observe an enhanced correlated insulating state at half-filling factor of TDBG as a result of the charge-transfer process between TDBG and COC. The temperature and magnetic-field dependence of this enhanced state are further studied. Our results demonstrate the influence of charge-related effect at the interface, and shed a light on a new route for manipulating the correlated states in graphene-based moiré systems using interfacial charge transfer process.

Quantum dot (QD)-superconductor hybrids have been established as a suitable platform for realizing Kitaev chains hosting Majorana bound states. Implementing these structures in a qubit architecture is expected to result in coherence times that scale exponentially with the lengths of the chains. To scale to longer systems, the phase differences between all superconducting segments in the chain need to be controlled. While this control has been demonstrated by using an external magnetic flux [ten Haaf et al., Nature (London) 641, 890 (2025); Bordin et al., Nat Commun 17, 2313 (2026)], ideally, it can be achieved with control over intrinsic system parameters [Liu et al., Phys. Rev. Res. 7, L012045 (2025)]. In this work, we investigate whether the relevant phase differences can be tuned through the spin degree of freedom in each QD or the chemical potential of the discrete bound states in the hybrid sections. We confirm that both these tuning knobs allow for controlling the phase difference in the couplings between neighboring QDs, bypassing the requirement to tune an external flux. However, we find that the amplitude of the phase shifts can deviate from a discrete $\pi$ shift. We introduce a spatial variation in the spin-orbit field as a possible mechanism to explain the observed behavior and comment on the consequences for experimentally creating long Kitaev chains.

It is established that the nonlinear anomalous Nernst effect (NANE), originating from Berry curvature near the Fermi energy, is symmetry-permitted only when the crystal symmetry in the transport plane of two-dimensional (2D) materials does not exceed a single mirror line. Here, we show that an applied direct electric field can lift this symmetry constraint, enabling an electric-field-induced NANE to emerge in time-reversal symmetric 2D systems with higher crystallographic symmetries. This electric-field-induced NANE originates from two contributions: the Berry connection polarization, which roots in the electric-field-corrected Berry curvature, and the anomalous-velocity-modified nonequilibrium Fermi distribution function. Additionally, we propose an alternating temperature gradient as a driving force instead of the conventional steady one, ensuring experimental detection of NANE via second-harmonic measurement techniques. The behavior of electric-field-induced NANE in the monolayer graphene has been theoretically and systematically investigated.

We investigate collective spin-wave excitations and curvature-driven instabilities in concentrically arranged nanotubes coupled via antiferromagnetic interlayer exchange. By solving the linearized Landau–Lifshitz equation including exchange, anisotropy, interlayer exchange coupling, and nonlocal dipolar interactions, we show that curvature substantially reshapes the spin-wave spectrum and the spatial structure of the eigenmodes. As the number of nanotubes increases, the spectrum evolves into a multiband structure with hybridized collective branches and surface-localized modes. In contrast to planar multilayers, the tubular geometry breaks the equivalence between inner and outer boundaries, producing asymmetric surface localization, curvature-induced shifts of the nodal structure, and nonreciprocal spin-wave propagation. We further analyze magnetic instabilities through the softening of the lowest spin-wave modes. For weak radial anisotropy, a uniform mode governs the instability, whereas above a critical anisotropy the soft mode occurs at a finite wave vector, signaling an instability toward a stripelike modulation along the nanotube axis. Although curvature shifts the instability thresholds, the characteristic modulation period remains nearly independent of the tube radius. The overall dynamical behavior of the coupled nanotubes can be understood in terms of an effective curvature-induced anisotropy, which unifies the spectral reconstruction and instability thresholds. These results establish tubular multilayers as a platform in which geometry controls both collective spin-wave excitations and instability-driven magnetic phases.