Transport experiments on two-dimensional superconductors often yield direction-dependent transition temperatures, raising the question of whether such a “double-$T_c$” reflects a true thermodynamic splitting or a transport artifact. To establish a baseline, we study a minimal anisotropic phase-only Josephson-junction array in equilibrium and under resistively shunted junction dynamics with fluctuating twist boundary conditions. The equilibrium model exhibits a single Berezinskii-Kosterlitz-Thouless transition. Out of equilibrium, anisotropic Josephson couplings and anisotropic dissipation reshape the linear $R\text{−}T$ curves in a finite-size, finite-current crossover regime, so that curve-shape criteria such as Halperin-Nelson fits and fixed-resistance thresholds yield an apparent double-$T_c$. In contrast, critical-scaling criteria—the universal exponent $\alpha =3$ and dynamic finite-size scaling—remain consistent with the single $T_{\mathrm{BKT}}$. A robust splitting that persists in the nonlinear critical scaling, such as that recently reported at ${\mathrm{KTaO}}_3$ interfaces, therefore, points to physics beyond this clean anisotropic baseline.

The layer-dependent Hamiltonians of parallel-stacked ${\mathrm{MoTe}}_2$ and ${\mathrm{WSe}}_2$ homobilayer moiré materials are topologically nontrivial, both in real space and in momentum space, and have been shown to support integer and fractional quantum anomalous Hall states, as well as antiferromagnetic and superconducting states. Here, we address the interplay between the antiferromagnetic and superconducting states observed in $t{\mathrm{WSe}}_2$ when the Fermi level is close to its $M$-point van Hove singularity and the displacement field is small. We combine density functional theory with path integrals to construct a minimal moiré band model that accounts for lattice relaxation along the $c$axis and perform Hartree-Fock calculations to identify competing charge and spin ordered states. For $t{\mathrm{WSe}}_2$ at $\theta =2.7^{\circ }$ and $\theta =3.{65}^{\circ }$, we find that a layer antiferromagnet, a stripe spin-density wave, and the ferromagnetic Chern insulator are the primary candidates for the ground state at zero displacement field, and argue that antiferromagnetic spin interactions on the next neighbor bond $J_2$ can induce a time-reversal symmetry breaking chiral superconducting state.

Perovskite oxides ${\mathrm{ABO}}_3$ host a rich interplay of charge, spin, lattice, and orbital degrees of freedom, giving rise to diverse quantum phenomena. In low-dimensional ${\mathrm{ABO}}_3$ systems, reduced symmetry can induce exotic quantum effects such as a two-dimensional electron gas and unconventional superconductivity. Using first-principles density-functional theory, tight-binding modeling, and symmetry analysis, we show that ultrathin two-dimensional (2D) ${\mathrm{ABO}}_3$ films—exemplified by ${\mathrm{SrTiO}}_3$—naturally break inversion symmetry, producing a spontaneous out-of-plane bulk photovoltaic (BPV) effect. This differs from previous studies that focused on in-plane BPV current signals and is more applicable and experimentally detectable. Such an effect is highly tunable via thickness, strain, surface termination, crystallographic orientation, and Moiré twisting. These findings are broadly applicable to a wide range of 2D perovskite oxides and other layer-resolved oxides.

The comprehensive description of both the electrical transport along conductive domain walls in lithium niobate single crystals and the charge injection at the interfacing metal electrodes, emerged to be a complex challenge. Recently, a heuristic evaluation allowed to postulate the “$R2D2$” equivalent-circuit model (consisting of two parallel resistor-diode pairs) to appropriately match the dc current-voltage (I-V) characteristics. Here, we carefully revisit the interfacial electrical behavior, i.e., the diode part of the equivalent circuit model, since many more processes beyond the diode-related electron hopping transport (HT) assumed so far, may concurrently occur, such as thermionic emission (TE), Fowler-Nordheim tunneling (FNT), space-charge limited conduction (SCLC), and others. The “$R2D2$” model thus needs to be generalized into an “$R2X2$” circuit model (with $X$ = HT, TE, FNT, SCLC, and others) to fit to the experimental data. Moreover, to check for the best I-V curve fitting to the different theories, we apply a higher-harmonic DW current-contribution analysis, i.e., an ac I-V inspection, that allows us to discriminate between all these possible models with much higher precision than from pure dc I-V curve fitting. Both the ac and dc analysis yield consistent results, finding that the FNT model accounts best for the domain-wall/electrode junctions investigated here.

We study the time-dependent triplet configuration, appearing under nonequilibrium conditions in a nanoscopic junction with two quantum dots (QDs) coupled in series between superconductor and normal metallic lead. We show that, in the situation when both QDs are singly occupied by identical spin electrons, the on-dot electron pairing is suppressed, which substantially affects the subgap charge transport. We investigate processes in which such a configuration can be temporarily encountered, either due to the initial conditions or by imposing the external magnetic field. Our analytical and numerical calculations provide estimations for the temporal scales, characterizing the evolution of the triplet configuration which could be manifested in the time-resolved tunneling measurements. Such nonequilibrium features of the triplet configuration might be relevant to operations on superconducting qubits, in their conventional and/or topological realizations.

Silver iodide (AgI) thin films offer a compelling platform for studying nonlinear optical phenomena due to their intrinsic noncentrosymmetric lattice and direct band gap. Here, we investigate the nonlinear optical properties of AgI thin films grown by physical vapor deposition that selectively produce zinc-blende $\left(\gamma \text{−}\mathrm{AgI}\right)$ and wurtzite $\left(\beta \text{−}\mathrm{AgI}\right)$ phases. Using a combination of polarization-resolved second-harmonic generation (SHG) and two-photon photoluminescence (2PPL) spectroscopy, we identify clear phase- and morphology-dependent anisotropic nonlinear responses. Triangular $\gamma \text{−}\mathrm{AgI}\left(111\right)$ flakes exhibit sixfold SHG symmetry and isotropic 2PPL emission, while rod-shaped $\beta \text{−}\mathrm{AgI}\left(101\right)$ samples display twofold-symmetric patterns in both SHG and 2PPL, which are explained by theories that integrate explicit polarization analysis using second- and third-order nonlinear susceptibilities. We estimate ${\chi }_{\mathrm{eff}}^{\left(2\right)}$ of 0.45 pm/V $\left(\gamma \text{−}\mathrm{AgI}\right)$ and 0.16 pm/V $\left(\beta \text{−}\mathrm{AgI}\right)$, respectively, after correcting for multiple internal reflections and generation of SHG within the AgI film and optical interference effect in the dielectric layers. These results identify AgI as a useful single-composition halide platform for studying phase-dependent nonlinearity and establish a realistic methodology for evaluating nonlinear susceptibilities in layered materials or thin films supported by a substrate.

Exceptional points (EPs) in non-Hermitian metasurfaces give rise to unusual wave phenomena and have attracted considerable interest for photonic applications. However, the analysis and design of EP metasurfaces are typically based on coupled-mode theory, which often relies on spectral fitting and can become computationally demanding. Here, we develop a quasinormal mode (QNM) coupling framework for the physical analysis and forward design of EP metasurface systems. An automated EP search algorithm is introduced to efficiently identify optimal configurations. Within this framework, the coupled eigenfrequencies are obtained directly from the QNMs of the constituent resonators rather than spectral fitting. Furthermore, we apply the proposed approach to the design of an EP metasurface sensor and evaluate its sensing response. The results demonstrate that the method provides an efficient and physically grounded route to the analysis and design of various EP metasurfaces.

Near-field radiative heat transfer (NFRHT) exceeds the blackbody limit through evanescent wave tunneling but faces scalability barriers due to nanoscale vacuum-gap constraints. To overcome this limit, the present study proposes a K-infiltrated ${\mathrm{SiO}}_2$ nanoporous hyperbolic metamaterial as a functional gap-filling medium. A fully coupled multiphysics framework—integrating fluctuational electrodynamics, conductive transport, and energy-conserving temperature stratification—resolves the radiation-conduction competition within the filler. Crucially, we demonstrate radiation-dominated heat transfer higher than conduction in solid-state systems: with a 100-nm-thick hyperbolic metamaterial filled between two doped silicon plates, radiative flux exceeds vacuum-gap NFRHT by 4 orders of magnitude, and even surpasses thermal conduction at ΔT > 300 K. This breakthrough stems from broadband hyperbolic dispersion and synergistic surface plasmon-hyperbolic polariton coupling, validated via spectral transmission peaks. By replacing vacuum with a bulk solid medium, this work provides a foundational understanding of radiation-conduction competition and electromagnetic mode coupling in nanoscale thermal transport, offering insights relevant to nanophotonics and thermal metamaterial research.

We investigate spin-valley instabilities and their connection to the magnetically ordered states recently observed in the twisted bilayer dichalcogenide ${\mathrm{WSe}}_2$ at a 5° twist angle. Starting from an effective three-orbital faithful Wannier model for the spin-locked moiré bands, combined with orbital-dependent Hubbard interactions, we analyze the evolution of magnetic instabilities as a function of carrier density using the matrix random phase approximation (mRPA) approach. By computing the Stoner boundary lines from the spin-valley susceptibilities over the electric field by a hole-filling phase diagram, we show that the spin-valley instabilities result in ordered states in the region close to the Lifshitz transition at the topmost moiré valence band, marked by crossing of the van Hove singularity in the density of states. These spin-valley-ordered states are dominated by interorbital spin-valley flips involving the $MM$ and $MX$ moiré orbitals and occur at different momenta in each side of the van Hove line, indicating a distinct spatial dependence of the spin-valley order parameter depending on the hole filling. Moreover, the corresponding Stoner boundaries exhibit strong fluctuations on its flanks, which can favor superconducting states in the regions close to the spin-valley-ordered ones. This mechanism provides a natural description for a reentrant superconducting dome consistent with the experimental results. As such, our results suggest spin-valley fluctuations near the van Hove line as the microscopic origin of the reentrant superconductivity in twisted ${\mathrm{WSe}}_2$.

We study tight-binding models in the crossover from hyperbolic to Euclidean lattices, realized through the successive insertion of Euclidean defects into hyperbolic lattices. We analyze how the holographic two-point boundary correlation function and bulk density of states evolve as defects are gradually introduced. We find that bulk properties are strongly affected by the presence of Euclidean defects, whereas boundary observables remain remarkably robust even at high defect fractions. This robustness indicates that essential features of boundary physics on hyperbolic lattices, which capture aspects of anti-de Sitter/conformal field theory (AdS/CFT)-like dualities in discrete systems, can be reproduced both experimentally and numerically without requiring perfectly hyperbolic lattices, thereby reducing the system size needed for implementation.

We present a theoretical investigation of the electronic band structure and optical properties of a two-dimensional anisotropic semimetal described by a tilted semi-Dirac type spectrum with a pair of Weyl nodes. We observe that a tilt along the quadratic direction can give rise to an energy imbalance between these nodes, contrary to the effect of tilt along the linear direction. We investigate the optical response of such a system subjected to an external ac bias, aiming to probe the energy imbalance between the nodes. We show that the anisotropic interband optical conductivity gives a clear signature of imbalanced nodes by exciting electrons at two different chemical potentials at near zero frequency, where the difference between these two chemical potentials is a direct measure of the energy imbalance. We also investigate the intraband dc conductivity, which reveals that, contrary to the tilted Dirac materials, tilt can convert a semi-Dirac material from a semimetallic phase to a metallic phase. Furthermore, we periodically drive the system with an external time-periodic perturbation to open up a topological gap at those nodes. We also show that the presence of imbalanced Weyl nodes prevents the semi-Dirac material from switching to a Chern topological phase even after opening topological gaps at the nodes, as the bulk remains gapless. Such state cannot be probed by the usual anomalous Hall response, as it will be overshadowed by the bulk contribution. Here, we show that those gaps at different chemical potentials can be probed by optical excitation. Finally, we extend our study to the nonlinear regime, where we particularly focus on second-harmonic generation in an inversion-symmetry-broken tilted semi-Dirac system. A clear signature of energy-imbalanced Weyl nodes can also be detected here.

We construct a two-dimensional bosonic symmetry-protected topological (SPT) paramagnet protected by an on-site $G={\mathbb{Z}}_4^{\times 3}$ symmetry, starting from a three-component ${\mathbb{Z}}_4$ Potts paramagnet on a triangular lattice. Within the group-cohomology framework, $H^3[G,U\left(1\right)]\cong {\mathbb{Z}}_4^{\times 7}$, we focus on a colorless cocycle representative obtained by antisymmetrizing the basic ${\mathbb{Z}}_4$ three-cocycle, and generate the corresponding SPT Hamiltonian via a cocycle-induced local unitary transformation $H^3[G,U\left(1\right)]\cong {\mathbb{Z}}_4^{\times 7}$ followed by symmetry averaging. For open geometry, we derive the boundary theory explicitly: one color sector decouples, while the nontrivial edge reduces to an interacting ${\mathbb{Z}}_4$ chain with next-nearest-neighbor constraints that admits a compact dressed-Potts form. Using DMRG we show that the boundary model is gapless, with the lowest gap scaling as $1/L$ and an entanglement-entropy scaling consistent with a conformal field theory of central charge $c=2.191\left(4\right)\simeq 11/5$. The rational value $c=11/5$ matches the coset $SU{\left(3\right)}_3/SU{\left(2\right)}_3$, making it a candidate for the continuum description of the ${\mathbb{Z}}_4^{\times 3}$ edge; we outline spectral and symmetry-resolved diagnostics needed to test this identification at the level of conformal towers beyond the central charge.

Coherent spin dynamics of localized ${\mathrm{Mn}}^{2+}$ spins are studied in a single (Cd,Mn)Te/(Cd,Mg)Te diluted-magnetic-semiconductor quantum well using a two-color pump-probe Faraday rotation technique. The initial phase of the manganese Larmor precession in magnetic field is measured at the maximum of exciton absorption, where the probe is set. The pump is detuned at lower energies with weak absorption of the quantum well excitons. The measured dependence of the initial phase on the pump power allows us to conclude that the manganese Larmor precession is induced by two mechanisms: the exchange field of optically oriented photogenerated holes and the magnetic field resulting from the inverse Faraday effect. The initial phase depends also on the strength of the external magnetic field. The modeled dependence of the phase on the pump power in various magnetic fields is in good agreement with the experimental data.

Layered two-dimensional electron systems exhibit both optical and acousticlike plasmons around the Brillouin-zone center. In the layered cuprate ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$, resonant inelastic x-ray scattering (RIXS) has detected corresponding acousticlike plasmons in a low-energy regime comparable to that of other collective excitations associated with distinct regions of the cuprate phase diagram. This overlap in energy scale raises the question of whether the acousticlike plasmons are significantly influenced by phase-specific electronic phenomena, including the pseudogap, charge and spin order, superconductivity, and strange-metal behavior. Here, we show that a single parameter set of the layered $t\text{−}J\text{−}V$ model, which incorporates strong correlations and the long-range Coulomb interaction $V$, consistently describes the acousticlike plasmon dispersion across all currently available RIXS data from the underdoped to the heavily overdoped regime. This transferability of a single parameter set exceeds that of earlier theoretical descriptions and supports a picture in which strong correlations persist into the heavily overdoped regime, while the collective plasmon mode exhibits only limited sensitivity to the phase-specific electronic phenomena that distinguish different regions of the phase diagram.

A monolayer graphene and its Dirac electrons can be equipped with an enhanced spin-orbit coupling (SOC) when proximitized by other van der Waals (vdW) materials, such as transition metal dichalcogenides (TMDs). In this work we analyze the features of the cyclotron resonance (CR) absorption at quantizing magnetic fields emerging in the presence of proximity-induced spin interactions, including the spin-pseudospin Rashba coupling. We evaluate the spin-textured wave functions of the Landau levels and calculate the absorption spectrum paying special attention to its spin proximity induced modifications. We reveal the formation of a fine double-peak structure of the main interband CR transitions, as well as the presence of additional spin-flip absorption, the combined cyclotron resonance (CCR), centered at different resonant frequencies. The selection rules for CCRs are identified and complemented by the perturbation theory analysis. We also discuss the polarization dependence of the absorption and the proximity-induced emerging magneto-optical responses. Our theory explains the effect of proximity-induced spin interactions for Dirac electrons cyclotron resonance and points out at its experimental verifications.

We study the topological properties of a one-dimensional quasiperiodic-potential-modulated mosaic trimer lattice. To begin with, we first investigate the topological properties of the model in the clean limit free of quasiperiodic modulation based on analytical derivations and numerical calculations of the Zak phase $Z$ and the polarization $P$. Two nontrivial topological phases corresponding to $1/3$ filling and $2/3$ filling, respectively, are revealed. Then we incorporate the mosaic modulation and investigate the influence of quasiperiodic modulation on the two existing topological phases. Interestingly, it turns out that quasiperiodic modulation gives rise to multiple distinct effects for different fillings. At $2/3$ filling, the topological phase is significantly enhanced by the quasiperiodic modulation, where a topologically trivial region adjacent to the original topological phase is converted into a topological one. Based on the calculations of polarization and the relevant level spacing, we explicitly present a corresponding topological phase diagram in the $\lambda \text{−}J$ plane. While for the $1/3$ filling case, the quasiperiodic modulation dramatically compresses the topological phase, and strikingly, further induces the emergence of reentrant topological phase transitions instead. Furthermore, we verify the topological phase diagrams by computing the many-body ground-state fidelity susceptibility for both the $1/3$ filling and the $2/3$ filling cases. Our work exemplifies the diverse roles of quasiperiodic potential in the modulation of topological properties, and will further inspire more research on the competitive and cooperative interplay between topological properties and quasiperiodic modulations.

We compute the critical exponents of the zero-temperature spin glass transition in a field on a one-dimensional long-range model, a proxy for higher-dimensional systems. Our approach is based on a novel loop expansion within the Bethe $M$-layer formalism, whose adaptation to this specific case is detailed here. The resulting estimates provide crucial benchmarks for numerical simulations that can access larger system sizes in one dimension, thus offering a key test of the theory of spin glasses in a field.

We employ optical pump-THz probe spectroscopy to chart the ultrafast superconductivity suppression in NbN over a broad range of excitation fluences. Our measurements uncover a pronounced lengthening of the superconductivity quenching time when the absorbed optical energy is close to the condensation energy of the superconductor, which constitutes a nonequilibrium analog of critical slowing down on a timescale comparable to that of superconducting fluctuations. Time-dependent Ginzburg-Landau simulations reproduce this behavior and ascribe it to the flattening of the free-energy landscape at the dynamical phase-transition boundary. Our findings represent a direct observation in real time of slowed-down superconductivity dynamics in proximity to a critical point and open a pathway for investigating out-of-equilibrium critical phenomena with time-resolved THz spectroscopy.