The superconducting version of a diode effect has been the subject of extensive research in the past few years. So far, the focus has almost exclusively been on charge transport, but a natural question is whether it is possible to obtain nonreciprocal spin transport without dissipation. Here, we demonstrate that it is possible to generate electrically tunable nonreciprocal spin transport carried by a supercurrent using superconductor/ferromagnet multilayers. The nonreciprocal spin supercurrent reaches an ideal efficiency of 100%, meaning that the spin-polarization of the critical current is finite in one flow direction whereas it vanishes in the other direction. We explain the underlying physics generating this phenomenon. This result provides a way to integrate nonreciprocal supercurrents with spin-polarization, offering new functionality in quantum technologies based on Josephson junctions.

HfRuP and ZrRuAs have garnered significant interest in recent years as potential topological superconductors. However, the mechanism underlying their superconducting pairing, particularly whether it is mediated by electron-phonon coupling (EPC), remains unresolved. Here, we conducted polarized and temperature-dependent Raman scattering experiments to comparatively investigate their EPC. Six Raman-active phonon modes were assigned for each compound based on polarized Raman spectra and first-principles calculations. Temperature-dependent Raman scattering measurements revealed a large and continuous softening of some low-energy phonon modes for both crystals in the measurement temperature range from $1.7\mathrm{to}300\mathrm{K}$. In HfRuP, the $E^{″}$ $\left(91.5{\mathrm{cm}}^{-1}\right)$ and $E^{\prime }$ $\left(102.9{\mathrm{cm}}^{-1}\right)$ modes exhibit phonon softening and linewidth broadening upon cooling. In ZrRuAs, the $E^{″}$ $\left(88.8{\mathrm{cm}}^{-1}\right)$ mode shows similar behavior. Furthermore, the $E^{\prime }$ mode in HfRuP $\left(357.2{\mathrm{cm}}^{-1}\right)$ and the $A_1^{\prime }$ mode in ZrRuAs $\left(171.1{\mathrm{cm}}^{-1}\right)$ exhibit conventional frequency hardening but anomalous linewidth broadening upon cooling. Our first-principles calculations attribute these anomalies to a resonancelike enhancement of the EPC between the Fermi-surface electrons and the Ru-dominated $E^{″}$ phonon mode. The electronic band structures also demonstrate that the enhancement stems from the exact matching in energy scale between the Ru-dominated low-frequency phonon modes and the distribution of their electronic densities of states around $E_F$. These results provide direct evidence that EPC drives the superconducting pairing in both compounds, highlighting the pivotal role of Ru atoms in these ternary transition metal pnictide superconductors.

Extensive investigations on the moiré magic angle have been conducted in twisted bilayer graphene, unlocking the mystery of unconventional superconductivity and insulating states. In analogy to the magic angle, here we demonstrate the concept of magic strain in graphene systems by judiciously tailoring mechanical relaxation (stretch and compression) which is easier to implement in practice. We elucidate the interplay of strain-induced effects and delve into the resulting unconventional superconductivity or semimetal-insulator transition in relaxation-strained graphene, going beyond the traditional twisting approach. Our findings reveal how relaxation strain can trigger superconducting transitions (with an ultraflat band at the Fermi level) or a semimetal-insulator transition (with a gap opening at the $K$ point of $0.39\mathrm{eV}$) in both monolayer and bilayer graphene. These discoveries open up another branch for correlated phenomena and provide deeper insights into the underlying physics of superconductors, which positions graphene as a highly tunable platform for different electronic applications.

Recent work has shown novel properties of twisted cuprates. In this paper, I point out that related phenomena occur intrinsically in bismuth-based cuprate superconductors due to the presence of the BiO supermodulation. As the ratio of the supermodulation potential to the superconducting energy gap increases, two critical points are found where semi-Dirac nodes form (that is, they have quadratic dispersion in one direction and linear dispersion in the orthogonal direction). The first critical point should be realized in Bi2212, the second in Bi2201. Implications of these findings are discussed.

The attractive Fermi-Hubbard model stands out as a simple model for studying the pairing and superconductivity of fermions on a lattice. In this article, we apply several many-body theories in the three-dimensional attractive Hubbard model. Specifically, we compare the results of various $GW$ methods with determinant quantum Monte Carlo simulations, and we observe that they provide reliable results in the weak- to intermediate-coupling regime. The critical exponents also agree well with the accurate results obtained from the three-dimensional $XY$ model. Additionally, we propose a method to determine the temperature at which the pseudogap appears. In the superconducting phase, we implement the covariance method within the $GW$ framework to calculate correlation functions. This method satisfies both the Ward-Takahashi identity (WTI) and the fluctuation-dissipation theorem, whereas the random phase approximation and the Bethe-Salpeter equation within $GW$ violate these principles. For systems with continuous spontaneous symmetry breaking, the WTI rigorously ensures the existence of massless Goldstone modes. Moreover, we numerically verify the appearance of Goldstone modes in the superconducting phase within the covariant-$GW$ approach. Based on the covariance method, we further incorporate corrections beyond the $GW$ approximation—a technique termed the post-$GW$ method which gives quite accurate results for the Green's function in the superconducting phase.

Double perovskites containing heavy transition-metal ions are an important family of compounds for the study of the interplay between electron correlation and spin-orbit coupling. Here, by combining magnetic susceptibility, heat capacity, and neutron scattering measurements, we investigate the dipolar and quadrupolar correlations in two prototypal rhenium-based double perovskite compounds ${\mathrm{Ba}}_2{\mathrm{YReO}}_6$ and ${\mathrm{Ba}}_2{\mathrm{ScReO}}_6$. A type-I dipolar antiferromagnetic ground state with a propagation vector $\mathbf{q}=(0,0,1)$ is observed in both compounds. At temperatures above the magnetic transitions, a quadrupolar ordered phase is identified. Weak spin excitations, which are gapped at low temperatures and softened in the correlated paramagnetic phase, are explained using a minimal model that considers both the dipolar and quadrupolar interactions. At larger wave vectors, we observe dominant phonon excitations that are well described by density functional calculations.

Understanding how to control changes in the electronic structure and related dynamical renormalizations by external driving fields is the key for understanding ultrafast spectroscopy and applications in electronics. Here, we focus on the band gap's modulation by external electric fields and uncover the effect of band dispersion on the gap renormalization. We employ the Green's function formalism using the real-time Dyson expansion to account for dynamical correlations induced by photodoping. The many-body formalism captures the dynamics of systems with long-range interactions, carrier mobility, and variable electron and hole effective mass. We also demonstrate that mean-field simulations based on the Hartree-Fock Hamiltonian, which lacks dynamical correlations, yields a qualitatively incorrect picture of band-gap renormalization. We find the trend that increasing effective mass, thus decreasing mobility, leads to as much as a $6\%$ enhancement in band-gap renormalization. Further, the renormalization is strongly dependent on the degree of photodoping. As the screening induced by free electrons and holes effectively reduces any long-range and interband interactions for highly excited systems, we show that there is a specific turnover point with a minimal band gap. We further demonstrate that the optical gap renormalization follows the same trend though its magnitude is altered by the Moss-Burstein effect.

Electronic structures of Cs- and Sb-terminated surfaces of a kagome superconductor ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ have been elucidated by means of scanning photoemission microscopy (SPEM). The observed band structure of the Cs-terminated surface is rather close to that of the bulk, while that of the Sb-terminated one is substantially modified around the $K/H$ point of the Brillouin zone. While the contrast between the Cs- and Sb-terminated regions is reduced below the charge density wave transition temperature, the Sb $5p$ band of the Cs-terminated region exhibits electronic inhomogeneity which slightly increases below it. The inhomogeneity of the Sb $5p$ band would be related to disorders of the out-of-plane Sb and relevant for the band folding along $\mathrm{\Gamma }-A$ with the charge density wave. The SPEM results suggest that the less inhomogeneous Cs termination is more suitable for interface of kagome superconductors. However, the inhomogeneity of Cs termination, which is significant at $\mathrm{\Gamma }/A$, noticeable at $K/H$, and negligible at $M/L$, is expected to affect the Sb $5p$-V $3d$ hybridization at the interface.

Non-Hermitian systems possess exotic localization phenomena beyond their Hermitian counterparts, exhibiting massive accumulation of eigenstates at the system boundaries with different scaling behaviors. In this study we investigate two weakly coupled non-Hermitian Hatano-Nelson chains under Möbius boundary conditions (MBCs) and reveal the coexistence of two distinct localization behaviors for eigenstates, namely, eigenstates exhibit non-Hermitian skin effect in one chain and scale-free localization in the other. Notably, the localization characteristics of eigenstates can be exchanged between the two chains, depending on their eigenenergies. This phenomenon is found to emerge from the critical behaviors induced by the weak interchain coupling, which can even be enhanced by MBCs in comparison to the system under other boundary conditions. Our findings deepen the understanding of non-Hermitian localization and criticality and offer insights into engineering tunable edge-localized states in synthetic quantum systems.

In this paper, we report the magnetoelectronic properties of high mobility InAs quantum point contacts grown on InP substrates. The InAs quantum well is embedded between ${\mathrm{In}}_{0.72}{\mathrm{Ga}}_{0.28}\mathrm{As}$ cladding layers and ${\mathrm{In}}_{0.81}{\mathrm{Al}}_{0.19}\mathrm{As}$ barrier layers, and is populated via self-accumulation. The one-dimensional (1D) conductance reaches a maximum value of 17 plateaus, quantized in units of $2e^2/h$, where $e$ is the fundamental unit of charge and $h$ is Planck's constant. The in-plane effective $g$ factor was estimated to be $-10.9\pm 1.5$ for subband $N=1$ and $-10.8\pm 1.6$ for subband $N=2$. Furthermore, a study of the nonmagnetic fractional conductance states at 0.2 ($e^2/h$) and 0.1 ($e^2/h$) is provided. While their origin remains under discussion, evidence suggests that they arise from strong electron-electron interactions and momentum-conserving backscattering between electrons in two distinct channels within the 1D region. This phenomenon may also be interpreted as an entanglement between the two channel directions facilitated by momentum-conserving backscattering.

Reciprocal optical binding forces between identical particles enable micron- and nanosized multiparticles to form a variety of stable static configurations. In general, the equilibrium interparticle distances are fixed and difficult to regulate. However, we demonstrate analytically that these distances can be continuously varied and even abruptly altered in dielectric-metal heterodimers driven by nonreciprocal transverse optical binding forces. These distances are crucial for determining the stable center of mass and configuration of the heterodimer. Specifically, the stability and equilibrium distances depend on the particle size and incident wavelength and can be tuned through the interplay between electric dipolar, magnetic dipolar, and electric-magnetic dipolar coupling components of the optical binding force. Moreover, the nonreciprocal nature of the binding force drives diverse nonequilibrium translations of the entire dimer as well as the attraction and repulsion of two particles. Importantly, the equilibrium distances, overall stability, and dynamics of the heterodimer can be modulated by the polarized angle of incident light. The results provide perspectives for the dynamical optical manipulation of multiparticle systems, shape-changing nanorobots, and phase-change arrays.

We systematically investigate the structural and electronic properties of twisted $h$-BN bilayers to understand the role of the twisting angle. Using first-principles methods with relaxation taken into account, we simulate $h$-BN bilayers with commensurate supercells with the smallest angle being $2.{88}^{\circ }$ until ${60}^{\circ }$. We find that the interlayer separation is not constant throughout each bilayer because of the various stacking patterns throughout the layers, which also plays a significant role in their interlayer charge redistribution. The calculations for the 110 generated structures show the existence of flat bands in several twisted $h$-BN bilayers, as well as the emergence of different trends in their properties as a function of the twist angle. These results are useful for establishing a systematic base line of registry-dependent relations for the development of more advanced computational methods to access incommensurate $h$-BN bilayers.

We study the interplay and competition between Kondo overscreening and superconductivity. The model we consider consists of a single $\mathrm{spin}\text{−}\frac{1}{2}$ quantum impurity at the edge of a quantum wire coupled to $\mathrm{spin}\text{−}1$ bulk fermions that interact attractively, generating a (superconducting) mass gap. The competition leads to a rich phase structure. We find that for strong Kondo coupling, there is a regime of phase space where the Kondo phase is stable with the impurity overscreened by a multiparticle Kondo effect, with a Kondo scale dynamically generated. When the bulk and boundary interaction strengths are comparable, we find that a midgap state appears in the spectrum and screens the impurity, while in the ground state, the impurity is unscreened. This midgap state is akin to the Yu-Shiba-Rusinov (YSR) states that exist in the entire phase space in the BCS superconductor. When the bulk superconducting interaction strength is stronger than the boundary Kondo interaction strength, the impurity can no longer be screened. Further, between the Kondo and YSR phases, we find a unique phase where, while the Kondo cloud overscreens the impurity, a boundary excitation exists that has vanishing energy in the thermodynamic limit.

The theory of Bloch dynamics for a single electron in a homogeneous electric field of arbitrary time dependence is established. The complete density matrix formulation for the dynamics is developed, and the two-band model is extracted. The two-band model is studied with emphasis on the interband coupling. A standard “$s\text{−}p$” two-band model is utilized from the nearest-neighbor tight-binding approximation to study the dynamics. In the analysis, the interband coupling paradigm is developed whereby the momentum component of the interband coupling is evaluated parametrically by using an analytically established band-matching condition. This leads to an interband coupling dependence on the band structure alone, and a significant reduction in computational complexity. The interband coupling parameter is then used to evaluate the transition probability as a function of external electric field over a wide range of field values. Results for the two-band current composites and each separate Bloch band are derived and analyzed. The temporal nature of the transition probability and current for a uniform electric field scenario is demonstrated and discussed.

Ferroelectric lithium tantalate (${\mathrm{LiTaO}}_3$) is widely used in electro-optic modulators and acousto-optic devices due to its strong nonlinear optical properties. However, unlike other electro-optic materials, the fundamental origin of its electro-optic response remains relatively unexplored. In this work, we use first-principles calculations to investigate the origin of the linear electro-optic effect in ${\mathrm{LiTaO}}_3$ by analyzing its electronic, ionic, and piezoelectric contributions to the electro-optic tensor. We find that the dominant component, $r_{33}$, is not primarily influenced by low-frequency soft phonon modes, as is typical in titanate-based materials. Instead, it is strongly affected by a specific frequency $A_1$ vibrational mode that significantly alters the Ta-O bond. Furthermore, we assess the piezoelectric contribution by calculating the piezoelectric strain tensor and the elasto-optic tensor. This study reveals the fundamental mechanisms driving the electro-optic response in trigonal ${\mathrm{LiTaO}}_3$ and provides insights for designing advanced nonlinear optical materials.

Single-photon sources (SPS) based on solid-state point defects are significant for advancing quantum technologies. Two-dimensional (2D) semiconductor materials with open structure offer advantages such as high photon extraction efficiency and the ability to integrate with photonic circuits. Recently, two-dimensional silicon carbide (2D-SiC) has emerged as a potential host material for SPS. In this study, first-principles calculations predict and identify two kinds of intrinsic point defects ${\mathrm{V}}_{\mathrm{Si}}{\mathrm{V}}_{\mathrm{C}}$ and ${\mathrm{V}}_{\mathrm{Si}}\mathrm{S}{\mathrm{i}}_{\mathrm{C}}$ in 2D-SiC, which stabilities were confirmed through defect formation energies and binding energies. Among the 18 identified transition pathways, two pathways $a_1\to b_1^{\left(1\right)}$ and $a_1\to b_1^{\left(2\right)}$ in the ${\mathrm{V}}_{\mathrm{Si}}{\mathrm{V}}_{\mathrm{C}}^{-}$ defect were selected based on their transition dipole moment and $\mathrm{\Delta }Q$ values, as they represent allowed optical transitions with superior optical properties. The results indicate that the pathway $a_1\to b_1^{\left(2\right)}$ exhibits the smaller Huang-Rhys factor of 1.474 and the larger Debye-Waller factor of 22.90%, and a short radiative lifetime of 3.4 ns. Additionally, the hyperfine tensor of the ${\mathrm{V}}_{\mathrm{Si}}{\mathrm{V}}_{\mathrm{C}}^{-}$ defect was calculated to facilitate the identification of defect centers. Our findings indicate that the ${\mathrm{V}}_{\mathrm{Si}}{\mathrm{V}}_{\mathrm{C}}^{-}$ defect in 2D-SiC is a potential candidate for SPS.

The intrinsic spin Hall effect (SHE) originates from spin-orbit coupling (SOC) and, featured by its low-energy dissipation, has emerged as a pivotal phenomenon with transformative potential in next-generation information technologies and quantum computing. Despite significant progress in investigating the SHE across various interaction regimes and advances in material engineering approaches, a fundamental principle governing the relationship between the intrinsic SHE and symmetry breaking remains elusive, especially in Rashba systems where spin is not a conserved quantity. Here, we employ a two-dimensional (2D) Dirac-Rashba model as a computational platform to investigate how interactions and symmetry alterations govern the SHE. We investigate the intrinsic SHE via adopting the unified theoretical framework demonstrated by Xiao et al. [Phys. Rev. B 104, L241411 (2021)], which assures a circulating spin current with null net flow at equilibrium. Three useful results are obtained: (i) even when the band spin splitting induced by SOC is strong enough, the intrinsic SHE might be absent because the Berry curvature could be missing; (ii) while Rashba SOC arises from the horizontal mirror plane symmetry $(z\to -z)$ breaking, the intrinsic SHE necessitates additional 2D inversion symmetry $\left[\right(x,y)\to (-x,-y\left)\right]$ breaking to manifest; (iii) the sign reversal of SHE is predicted by altering the symmetry breaking-induced potentials, which are controllable through vertical strain experimentally. Our results pave an insight for 2D SHE manipulation vias symmetry engineering.