We theoretically study the Josephson effect in ultracold Fermi gases, where the two sides of the Josephson junction are independently tuned to different regions of the Bardeen-Cooper-Schrieffer (BCS)-Bose-Einstein condensation (BEC) crossover. Using the nonequilibrium Green's function approach combined with the tunnel Hamiltonian formalism and a mean-field approach, we evaluate the DC and AC Josephson currents throughout the entire crossover region. We calculate the DC Josephson current as a function of interaction strength by tuning both sides of the junction synchronously from the BCS to the BEC regimes, and give the asymptotic expression of the current in the deep BCS and BEC limits. We also study the AC Josephson junction through the interaction-asymmetric junction by fixing the interaction in one reservoir and tuning that of the other one. A peak of the tunneling current is found when one side is fixed in the BCS limit and the other side is tuned into the BEC regime, which corresponds to the interaction-biased Riedel peak. Our results indicate the competition between contributions of increasing pair spectral weight and decreasing chemical potential to Josephson tunneling throughout the BCS-BEC crossover, and demonstrate the realization of the Riedel peak in strong-coupling quantum gases.

The $\eta$-pairing states are the exact eigenstates of the hypercubic Hubbard model, which exhibit an anomalous logarithmic scaling of entanglement entropy. It has been shown that $\eta$-pairing states are still exact eigenstates even in multiband systems, provided interband coupling is negligible on the flatband [M. Tovmasyan et al., Phys. Rev. B 94, 245149 (2016); J. Herzog-Arbeitman et al., Commun. Phys. (2026)]. However, typical flatband systems such as Lieb and Kagome lattices often feature band touchings, where interband coupling effects play a role. As an example of such a system, we investigate the deformation of $\eta$-pairing states in the Creutz ladder model with the interband coupling effect. Our results show that the interband coupling introduces effective nonlocal interactions within the flatband. In contrast to previous studies of $\eta$ pairing in isolated flatband systems, here the flatband is coupled to a nearby dispersive band, and we find that the $\eta$-pairing states persist in a modified form with logarithmic entanglement scaling. We observe the suppression of the entanglement entropy and the violation of the spectrum generating algebra. Interestingly, these effects persist even in the limit of infinitesimally small interband coupling. These findings illuminate the robustness and limitations of $\eta$ pairing in realistic setups, offering insights into the physics of interacting flatband systems.

The two-dimensional $M{A}_2{Z}_4$ material family has emerged as a research frontier in condensed matter physics and materials science due to its excellent stability and tunable electronic properties. While recent investigations have focused predominantly on their valley- and spin-related physical characteristics, exploration of their orbital Hall effect remains relatively insufficient. In this work, we systematically investigate the band structure and spin/orbital transport properties of monolayer ${\mathrm{MoSi}}_2{\mathrm{P}}_4$ through first-principles calculations and effective $k$·$p$ model analysis. The results show that ${\mathrm{MoSi}}_2{\mathrm{P}}_4$ exhibits an intrinsic orbital Hall effect. It demonstrates a pronounced orbital Hall conductivity near the Fermi level while maintaining relatively weak spin Hall conductivity. We further find a finite orbital Nernst response. Strain engineering studies on monolayer ${\mathrm{MoSi}}_2{\mathrm{P}}_4$ reveal that biaxial strain can induce a transition from a direct to an indirect bandgap. Despite this band structure change, the orbital Hall effect demonstrates remarkable robustness within a certain strain range. More importantly, the total orbital Nernst conductivity exhibits sign-tunable behavior under strain modulation, while the $\mathrm{\Gamma }$-region contribution is strongly enhanced when tensile strain shifts the valence band maximum to $\mathrm{\Gamma }$.

The ability to control superconducting pairing symmetry is crucial for designing unconventional and topological superconductors, yet practical tuning parameters beyond chemical doping remain limited. In this study, we investigate the effect of a tunable sublattice staggered potential on the pairing symmetry in the doped honeycomb Hubbard model. Determinant quantum Monte Carlo at finite temperature and constrained-path quantum Monte Carlo at zero temperature are employed to compute spin susceptibilities and pairing correlations in different channels. We find that increasing the staggered potential suppresses antiferromagnetic fluctuations, and at low doping, induces a transition in the dominant pairing tendency from $d+id$-wave to $f_n$-wave, with consistent results from both quantum Monte Carlo methods. In contrast, at higher doping levels, the system remains dominated by $d+id$-wave pairing even under an enhanced staggered potential. Moreover, strengthening the on-site interaction $U$ enhances the dominant pairing channel, underscoring the essential role of electronic correlations. Our results establish the staggered potential as a practical band-engineering tool for selecting unconventional pairing symmetries without varying the doping concentration, providing inspiration for designing graphene-based artificial superconductors and related doped band insulators such as ${\mathrm{Li}}_x\mathrm{MNCl}$.

Beyond conventional electronics, the Schottky barrier (the charge-transfer barrier at a metal-insulator interface) is an important parameter for the interfacial charge transfer controlling the device performance, efficiency, and stability across diverse technologies. Semilocal density functional theory often fails to predict the barrier with the necessary accuracy. These exchange-correlation functionals suffer from a self-interaction error that may result in band misalignment. In many transition-metal oxides, the valence-band maximum is dominated by localized $\mathrm{O}\text{−}2p$ orbitals, making it particularly sensitive to this error. The problem can be mitigated using a Hubbard U correction that reduces the self-interaction error for the targeted correlated manifold, thereby improving the resulting band alignment. Using a Materials Project dataset screening workflow, we identify oxides with localized $\mathrm{O}\text{−}2p$ states near the valence-band maximum, select systems where the experimental barrier height is known, and show that applying U to oxygen states brings the Schottky barrier in better agreement with experiment.

Terahertz spectroscopy provides unique access to molecular fingerprint regions, but suffers from weak light-matter interaction due to the dimension mismatch between the terahertz wavelength and the molecule. Here, an all-dielectric metasurface strategy inspired by bound states in the continuum (BICs) is proposed for nanoscale-level terahertz molecular sensing with tailored functionalities. Through the temporal coupled-mode theory, it reveals that the molecular signal can be enhanced by two efficient approaches: increasing the coupling coefficient $\mu$, or decreasing the radiation rate ${\gamma }_r$. Using the lossless symmetry-broken quasi-BIC dimerized grating coupled with the $\alpha$-lactose molecules as an example, it demonstrates the significant enhancement, yet with different trends for $\mu$-tailoring and ${\gamma }_r$-tailoring sensing approaches. Further combined with the angle-multiplexed mechanism, the symmetry-broken quasi-BICs enable the retrieval of terahertz vibrational fingerprints from molecular layers as thin as 1 nm, with an enhancement factor of three orders of magnitude. This work not only reveals the powerful capability of BIC within an all-dielectric platform for nanoscale terahertz detection, pushing terahertz sensing into unprecedented deep-nano levels, but also opens new avenues for developing advanced terahertz photonic devices.

The synthesis of the high-$T_{\mathrm{c}}$ superhydride ${\mathrm{CaH}}_6$ has stimulated significant interest in understanding synthesis pathways for metastable hydrides. However, the microscopic mechanisms governing such hydrogenation reactions remain poorly understood. Here, we show that machine-learning potential molecular dynamics simulations can reproduce and distinguish competing reaction pathways leading to metastable and stable hydrides. By simulating hydrogenation reactions at ${\mathrm{CaH}}_2\text{/}{\mathrm{H}}_2$ and ${\mathrm{CaH}}_4\text{/}{\mathrm{H}}_2$ interfaces, we identify two distinct pathways that produce clathrate-type ${\mathrm{CaH}}_6$ and A15-type ${\mathrm{CaH}}_{5.75}$, respectively. ${\mathrm{CaH}}_{5.75}$ lies on the convex hull but requires extensive Ca sublattice rearrangement and therefore forms only at elevated temperatures. In contrast, ${\mathrm{CaH}}_6$ becomes kinetically accessible when ${\mathrm{CaH}}_2$ is used as the precursor. The crystallographic compatibility between the Ca sublattice of ${\mathrm{CaH}}_2$ and the body-centered cubic framework of ${\mathrm{CaH}}_6$ enables a martensitic-like topotactic transformation that bypasses the reconstructive pathway leading to ${\mathrm{CaH}}_{5.75}$. These results reveal how precursor structure and thermodynamic stability compete to determine superhydride formation pathways and demonstrate that machine-learning molecular dynamics can directly capture the kinetic selection of metastable phases in reactive materials systems.

We revisit the quantum annealing problem in the non-Hermitian transverse-field Ising model. We determine, both analytically and numerically, the intrinsic transition probabilities and the resulting defect density. Our results reveal that, unlike the Hermitian case where defect production is dominated by modes near the gap-closing point, the non-Hermitian dynamics involve significant contributions from broad momentum sectors. We find that, depending on the dissipation strength, the defect density exhibits standard Kibble-Zurek scaling, anti-Kibble-Zurek behavior, and a suppression faster than the Kibble-Zurek prediction. We demonstrate that these deviations from the standard Kibble-Zurek scaling can be understood in terms of the underlying excitation probabilities. Specifically, the fast decay of the defect density originates from a vanishing excitation probability spanning a range of annealing times across all allowed modes, even at the gap-closing points. In contrast, the anti-Kibble-Zurek behavior arises from supplementary excitations facilitated by dissipation over a broad range of allowed modes, particularly those situated away from the gap-closing region.

Quantum spin liquids exhibit fractionalized spin excitations as a consequence of strong quantum many-body effects and have therefore attracted considerable attention. The kagome antiferromagnetic Heisenberg model is a promising candidate for realizing a quantum spin-liquid ground state; however, the nature of its excitation spectrum remains controversial, particularly for the presence of a spin gap and the gauge structure coupled to fractional quasiparticles. To address these issues, parton approaches have been extensively employed in theoretical studies, where spin operators are represented in terms of either fermionic or bosonic quasiparticles; the former approach is known as the Abrikosov fermion method, while the latter is referred to as the Schwinger boson method. Thus far, these approaches have been pursued independently, and it has remained unclear how the results obtained from these two different frameworks compare with each other, particularly with respect to the spin dynamics and gauge structure of the kagome antiferromagnet. Here, we investigate the dynamical spin structure factor of the antiferromagnetic Heisenberg model with a Dzyaloshinskii-Moriya interaction on a kagome lattice, which is relevant to the material herbertsmithite, by employing both the Abrikosov fermion and Schwinger boson approaches. We find that the dynamical spin structure factor obtained from the Abrikosov fermion mean-field theory exhibits dome-shaped features, and that its continuum structure significantly depends on the gauge structure of the spin-liquid Ansatz. On the other hand, the Schwinger boson mean-field theory yields a concave-down structure in the low-energy region of the dynamical spin structure factor, which is distinct from that obtained using the Abrikosov fermion approach. Moreover, the low-energy gap is substantially reduced, and the low-energy spectral weight is enhanced, by incorporating many-body effects beyond the mean-field approximation, which is consistent with experimental observations. Our results suggest the importance of many-body effects in the Schwinger boson theory for capturing the low-energy spin dynamics of kagome antiferromagnets.

We study the half-filled single-band Hubbard model on the Shastry-Sutherland lattice with nearest-neighbor hopping $t$, incorporating (i) a frustrating diagonal hopping $t^{\prime }$ to probe the emergence of spin-liquid behavior, and (ii) an additional Heisenberg exchange $J$ that explicitly stabilizes plaquette-singlet correlations. Using the variational cluster approximation (VCA) with exact diagonalization at zero temperature on an eight-site cluster, we map the phase diagrams in the $(U/t,t^{\prime }/t)$ and $(U/t,J/t)$ parameter planes. In the $(U/t,t^{\prime }/t)$ plane, our analysis uncovers a competition between Néel antiferromagnetic (AFM) order with staggered magnetization and a nonmagnetic regime lacking conventional order, consistent with a nonmagnetic insulating phase that may be related to the spin-liquid-like regimes reported in previous studies. In contrast, the $(U/t,J/t)$ phase diagram exhibits a competition between the Néel antiferromagnet and a solid valence-bonding valence bond plaquette (PS), where spins form localized singlet plaquettes. Most notably, we observe that the transition from the PS phase to the Néel AFM phase is a first-order phase transition, with a discontinuous jump of the order parameters at the phase boundary, in quantitative agreement with high-pressure heat-capacity measurements on ${\mathrm{SrCu}}_2{\left({\mathrm{BO}}_3\right)}_2$ [J. Guo et al., Commun. Phys. 8, 75 (2025)]. Thus, our VCA analysis underscores the subtle interplay of geometric frustration, quantum fluctuations, and dimensionality, and elucidates the crucial role of short-range correlations in stabilizing and competing ground states of frustrated quantum magnets.

We show that a three-dimensional superconductor with a non-Abelian SU(2) order parameter can support an extended resistive regime—a Bose metal, in which transport is carried by bosonic electron-Majorana bound states—separating a uniform superconductor from a pair-density-wave (PDW) phase. The setting is a solvable Kondo lattice model introduced previously by the present authors, in which Kondo screening of a Yao-Lee ${\mathbb{Z}}_2$ spin liquid generates an order parameter with SU(2), rather than conventional U(1), symmetry, containing both superconducting and spin-density-wave components. Two effects cooperate to make fluctuations anomalously strong in three dimensions: the vanishing of the quadratic superconducting stiffness near the Lifshitz point where the optimal pairing momentum shifts from zero to finite $Q$, and the enlarged SU(2) order-parameter manifold. Building on our prior result that doping away from half-filling drives amplitude-modulated PDW order via finite-momentum electron-Majorana condensation, we analyze the fluctuation-dominated regime above that phase using a nonlinear sigma model. We find that the order-parameter propagator develops a ring of soft modes throughout the disordered phase, and that at the smallest temperatures the resulting resistivity $R\sim T^3$ in three dimensions.

We consider states of BCS form in the two-dimensional (2D) Hubbard model which, starting from some arbitrary point in state space in the neighborhood of a Hartree-Fock ground state, are relaxed within that BCS ansatz to local minima of the energy. As in the Hartree-Fock approximation, there are a vast number of local minima, nearly degenerate in energy. What is new and unlike the conventional Hartree-Fock states is that there is a region in parameter space where these local minima are clearly associated with $d$-wave condensates of the form $d_{x^2-y^2}$ in the underdoped region. There are also indications of $d_{xy}$ condensation in the overdoped region, at least in this approximation to the 2D Hubbard model, as well as condensates over a range of parameters on triangular lattices.

Hydrides and solid hydrogen have long been considered potential high-temperature, and even room-temperature, superconductors, owing to the exceptionally high Debye temperature provided by their hydrogen atoms. However, we observed unexpected suppression of superconductivity in yttrium hydrides and metallic hydrogen systems. Our study demonstrates that the vibrational characteristics of the hydrogen sublattice constitute a critical factor influencing superconducting transition temperatures. We find that in H-poor yttrium hydrides, the anomalously low superconducting transition temperature originates from hydrogen-dominated acoustic-like vibrations. Strikingly, even in fcc metallic hydrogen—which exhibits the highest Debye temperature among known systems—the acoustic-like vibrational behavior of hydrogen results in an extremely weak polarization field and negligible electron-phonon coupling, severely limiting superconductivity. While alkali metals have long been regarded as the closest realization of an ideal free-electron metal, we demonstrate that fcc metallic hydrogen actually represents the closest embodiment of this fundamental model. Furthermore, our study reveals that the zero-resistance state in fcc metallic hydrogen originates from negligible electron-lattice scattering, rather than the suppression of transport electron scattering by superconducting gap pairs as predicted by BCS theory. Consequently, the transition to zero resistance in fcc metallic hydrogen occurs without passing through a thermodynamic phase transition of electron Cooper pair condensation, but rather manifests as a natural consequence of its perfect metallic properties.

Transconductance is a central figure of merit in field-effect transistors, typically governed by charge accumulation and carrier mobility. In multilayer ${\mathrm{WSe}}_2$ transistors, however, we show that the transconductance carries a nonlinear transport signature of intervalley carrier redistribution between the $K$ and $\mathrm{\Gamma }$ valleys. This valley-crossover contribution suppresses transconductance in bilayer ${\mathrm{WSe}}_2$ and reverses sign in trilayer, while remaining absent in single-valley systems. Unlike extrinsic mechanisms such as trap-state filling or contact resistance, the anomaly does not affect the subthreshold swing within this mechanism and cannot be reproduced within conventional single-valley transport models. Introducing the valley susceptibility ${\chi }_v\equiv \partial f_{\mathrm{\Gamma }}/\partial V_{GS}$, bounded by an intrinsic thermodynamic limit ${\left(4k_{B}T\right)}^{-1}$, we quantify this response and show that it reaches $\sim 0.20{\mathrm{V}}^{-1}$ in bilayer ${\mathrm{WSe}}_2$ near threshold at room temperature. The sign, magnitude, and temperature dependence of the anomaly provide directly measurable fingerprints of valley thermodynamics, establishing transconductance as an electrical probe of internal electronic degrees of freedom and revealing a primarily unexplored nonlinear response in standard transistor measurements.

Higher-order symmetric $X$-wave magnets consist of two groups. One includes $d$-wave, $g$-wave, and $i$-wave altermagnets, while the other includes $p$-wave and $f$-wave odd-parity magnets. Recently, the possibility of $h$-wave magnets has been discussed. Motivated by this development, we systematically construct an $X$-wave magnet with $(N_X+1)$ nodes in three dimensions from an $X$-wave magnet with $N_X$ nodes in two dimensions by means of a dimensional extension, where $N_X=1,2,3,4,6$ for $X=p,d,f,g,i$, respectively. Based on this method, we predict $j$-wave magnets in three dimensions. Then, we argue how to identify each of these $X$-wave magnets experimentally. We show that the $X$-wave magnet is completely identified by measuring the nonlinear spin currents. In particular, we predict that there are no spin currents other than the fourth-order ones such as ${\sigma }_{\text{spin}}^{x^{3}y;z}$ in $h$-wave odd-parity magnets in three dimensions and the sixth-order ones such as ${\sigma }_{\text{spin}}^{x^{5}y;z}$ in $j$-wave odd-parity magnets in three dimensions. They function as spin-current rectifiers because the spin current exhibits unidirectional flow independent of the applied electric field.

Motivated by ongoing interest in the universal behavior of the Hubbard model of spinning electrons on honeycomb and $\pi$-flux lattices at the semimetal–Mott insulator phase transition, we formulate the three-dimensional (3D) chiral Heisenberg model, a theory of relativistic fermions in three spacetime dimensions, as a lattice field theory using domain wall fermions. The contact interaction term preserves an SU(2) global symmetry. We perform numerical simulations using the rational hybrid Monte Carlo algorithm on system sizes $L^3\times L_s$, with $L\in \{8,...,24\}$ and domain wall separation $L_s\in \{8,16,24\}$. We locate the phase transition corresponding to spontaneous $\mathrm{SU}\left(2\right)\to \mathrm{U}\left(1\right)$ breaking, yielding critical exponent estimates ${\nu }^{-1}=0.63\left(3\right)$ and ${\eta }_{\mathrm{\Phi }}=1.42\left(8\right)$. These values are considerably removed from estimates obtained from simulations performed in (2+1)D, i.e., with the time and spatial directions treated differently, but align more closely with analytic estimates obtained using 3D covariant field theory. We also present results for the fermion correlator, ultimately needed for the determination of the exponent ${\eta }_{\mathrm{\Psi }}$, highlighting the need to rotate the fermion source to a common reference direction in isospace to obtain a signal.