Long-range bipartite entanglement (LBE) and its distribution properties are studied in XXZ spin chains with exponential and power-law long-range interactions (ELRIs and PLRIs). LBE quantified by two-qubit concurrence decays exponentially along with two-site distance in the infinite chain with ELRIs in the thermodynamic limit, and the long-range behavior of two-spin entanglement can detect the quantum phase transition and identify different quantum phases away from the critical point. Moreover, a fine-grained LBE distribution relation is obtained for the infinite XXZ spin chain. On the other hand, in the finite XXZ spin chain with conventional PLRIs, the long-range concurrence decays algebraically and the total one is no longer monotonic along with the chain length. The total LBE distribution property can exhibit a piecewise function, which has a close relationship with the decaying mode and strength of PLRIs. These LBE relations can be regarded as the generalization of Koashi-Bužek-Imoto bound for the prototypical long-range XXZ model, having potential applications in quantum information processing.

We investigate the effect of white-noise disorder on the local phase stiffness and thermodynamic properties of a two-dimensional $s$-wave superconductor. Starting from a local attractive model and using path-integral formalism, we derive an effective action by decoupling the superconducting order parameter into amplitude and phase components in a gauge-invariant manner. Perturbative techniques are applied to the phase fluctuation sector to derive an effective phase-only XY model for disordered superconducting systems. Solving the saddle-point Green's function using Bogoliubov-de Gennes theory, we calculate the distributions of nearest-neighbor couplings for various disorder strengths. A single-peak distribution is observed for low disorder strength, which becomes bimodal with one peak at negative couplings as the disorder strength increases. The local phase stiffness remains randomly distributed throughout the lattice and shows no correlation with pairing amplitudes. The temperature dependence of the superfluid stiffness ($J_s$) is studied using Monte Carlo simulations. At strong disorder and low temperatures, $J_s$ increases with increasing temperature, exhibiting anomalous behavior that may indicate the onset of a glassy transition. Additionally, calculations of the Edwards-Anderson order parameter in this disorder regime suggest the emergence of a phase-glass state at very low temperatures.

Scanning tunneling spectroscopy experiments on a number of cuprate superconductors have revealed that these materials are highly inhomogeneous. However, even though this inhomogeneity is well-characterized experimentally, a theoretical understanding of the effect of an inhomogeneous superconducting $d$-wave order parameter on various observables is still not complete. Here, we focus on the particular role played by the length scale of superconducting order-parameter inhomogeneity. We make use of a model involving square patches tiling the system, with each patch hosting a broadly distributed random value of the $d$-wave parameter. By using large-scale simulations, we are able to study how the size of the patches affects the correspondence between various measures of the superconducting gap and the underlying order parameter. If the length scale of the inhomogeneity is smaller than the average superconducting coherence length, the resulting $d$-wave superconductor is homogeneous. However, when the order parameter varies on the scale of the coherence length, we find the emergence of a striking low-energy–high-energy dichotomy, in which the low-energy regime is homogeneous while the high-energy states are strongly inhomogeneous. Kinks in the local spectra are found at the energy demarcating the homogeneous-inhomogeneous transition. We also observe that the gap extracted from the low-energy slope of the local density of states is extremely uniform. We find in both of these regimes that the distribution of the spectral gap is narrower than that of the order parameter; these start to match only when the size of the patches becomes parametrically larger than the coherence length. We comment on the applicability of these results to the cuprates, discuss the limitations of the inhomogeneous $d$-wave model, and point out where beyond-mean-field correlation effects are likely to be present in addition to inhomogeneity.

Cerium monopnictide CeSb is a low-carrier-density Kondo lattice semimetal with a complicated magnetic phase diagram. Recently, novel physical phenomena such as a pronounced angle-sensitive negative magnetoresistance, a magnetic topological quantization, and a quantum oscillation in magnetoresistance have been observed in CeSb. However, the mechanism of these novel physical phenomena remains unresolved. Herein, the magnetism and magnetic structure of CeSb-related Kondo lattice semimetal ${\mathrm{Ce}}_{0.9}{\mathrm{La}}_{0.1}\mathrm{Sb}$ (CLS) is investigated via neutron diffraction measurements. In contrast with CeSb, CLS exhibits several outstanding features of the magnetism and magnetic structure. CLS shows the type-I antiferromagnetic structure, in which its ferromagnetic layers are antiferromagnetically stacked along the interplane direction with the periodicity of a unit cell. Moreover, a ferromagnetic component is clearly observed without applying any magnetic field, and various magnetic structures strongly compete with each other along with a large temperature hysteresis. These findings may facilitate the in-depth understanding of the novel physical phenomena recently observed in CeSb.

Two-dimensional cobalt-based honeycomb oxide ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ is an important candidate for the realization of Kitaev physics and may provide a future platform for quantum computation and quantum technology. Here, for the quasi-two-dimensional ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ single crystals, we present detailed temperature and polarization-dependent inelastic light scattering (Raman) measurements. Our investigation uncovers the Raman spectroscopic signature of underlying multiple phase transitions i.e., a long-range antiferromagnetic transition $\left({\mathrm{T}}_{\mathrm{N}}\right)$ at ∼30 K, a ferroelectric transition $\left({\mathrm{T}}_{\mathrm{FE}}\right)$ at ∼70 K, and a crossover from a pure paramagnetic phase to a quantum paramagnetic phase around ∼150 K reflected in the renormalized self-energy parameters of the Raman active phonon modes. A distinct signature of spin reorientation deep into the antiferromagnetic phase around ${\mathrm{T}}_{\mathrm{SR}}\sim 17$ K is observed, marked by the clear change in the frequency and linewidth slopes. We also observed an asymmetric phonon mode in the low-frequency region, and it appears below the transition temperature ∼50 K, attributed to the magnetic excitations other than the magnon. The Raman signature of multiple crystal-field excitations at low temperature along with lifting of the Kramer's degeneracy is also observed.

Conventional treatments of Josephson junctions (JJs) are typically not current conserving. In the mean-field Bardeen-Cooper-Schrieffer theory, current conservation is only guaranteed if the superconducting order parameter is treated self-consistently. We show that this requirement has significant consequences for the current-phase relation (CPR) in certain regimes, where the current density in the superconducting leads is non-negligible. To this end, we introduce a numerical method for the self-consistent treatment of the Bogoliubov–de Gennes equations with current conservation for quasi-one-dimensional superconductor-normal (metal)-superconductor (SNS) JJs. Our model incorporates a phase gradient of the order parameter in the leads, which is set to match the Josephson current through the weak link. We compare our method to standard, noncurrent conserving approaches by calculating the CPR for SNS JJs while varying lengths and gate voltages controlling the normal metal. We show that current conservation has significant implications for the Josephson harmonics and can weaken or even reverse forward skewness of the CPR.

Topological superconductivity (TS) has been discussed widely in many superconducting systems with different symmetries, such as time-reversal symmetry, mirror symmetry, inversion symmetry, etc. In this paper we focus on the effects of the combined space-time inversion symmetry $PT$ on the gapped TS. By using Clifford algebra, we find that only one-dimensional (1D) and two-dimensional (2D) superconducting systems with $C^2={\left(PT\right)}^2=1$ ($C$ is particle-hole operator) can be topologically nontrivial, different from the conventional superconducting classifications. Starting from the minimum Dirac model, we construct the representative 1D and 2D models, which only show topology with $PT$ symmetry. These nontrivial models are called Stiefel-Whitney TS, for which the Hamiltonian and wave functions of the system can be real up to a basis choice. In terms of the 2D model, Stiefel-Whitney TS not only corresponds to the second-order TS having zero energy corner modes, but also can show topologically protected nodal points in the Brillouin zone. The possible experimental realizations for 1D and 2D Stiefel-Whitney TS from superconducting proximity effects are pointed out. We expect that these theoretical results will arouse the explorations on Stiefel-Whitney TS.

In this paper, we investigate the impact of nonlocal correlations on charge fluctuations in the two-dimensional single-band Hubbard model close to the Mott metal-to-insulator transition, employing the ladder dynamical vertex approximation. At half filling and for interaction strengths and temperatures where the system is in the Mott insulating phase, charge fluctuations are strongly suppressed. Under these conditions, dynamical mean-field theory (DMFT) calculations predict a strong enhancement of the charge susceptibility at small (electron or hole) doping. However, these DMFT results include only the effects of purely local correlations despite the importance of nonlocal correlations in two-dimensional systems. We have, hence, carried out ladder dynamical vertex approximation $\left(\mathrm{lD}\mathrm{\Gamma }\mathrm{A}\right)$ simulations which allow for the inclusion of such nonlocal correlation effects while retaining the local ones of DMFT. Our $\mathrm{lD}\mathrm{\Gamma }\mathrm{A}$ numerical data show that close to half filling the large uniform charge susceptibility of DMFT is strongly suppressed by nonlocal fluctuations but gradually increases with (electron) doping. At a certain doping value, charge fluctuations eventually become larger in $\mathrm{lD}\mathrm{\Gamma }\mathrm{A}$ with respect to DMFT, indicating that the absence of nonlocal correlations underestimates the mobility of the charge carriers in this parameter regime. This metallization effect is also reflected in an enhancement of the $\mathrm{lD}\mathrm{\Gamma }\mathrm{A}$ kinetic and potential energies and a corresponding reduction of the (absolute value of the) $\mathrm{lD}\mathrm{\Gamma }\mathrm{A}$ Matsubara self-energy with respect to DMFT.

The CoSi family of materials (CoSi, CoGe, RhSi, and RhGe) forms a cubic chiral structure and hosts unconventional multifold chiral fermions, such as spin-1 and spin-$\frac{3}{2}$ fermions, leading to intriguing phenomena like long Fermi arc surface states and exotic transport properties. Recent interest in the phonon behavior in chiral materials has been growing due to their unique characteristics, including topological phonons, protected surface states, and chiral phonons with nonzero angular momentums. In this study, we explore the topological and chiral phonon behavior in RhGe, using first-principles density functional theory calculations as well as the symmetry and topological analysis. We uncover six spin-1 triply degenerate nodal points at the $\mathrm{\Gamma }$ point and six charge-2 double Weyl points at the $R$ point in the Brillouin zone (BZ). Interestingly, these topological features are identical to that in the electronic band structure of the same material without electron spin-orbit coupling. We expect that this finding not only applies to the CoSi family but also is universal. Secondly, we find that chiral crystal RhGe hosts chiral phonon modes with a phonon angular momentum (PAM) and an associated phonon magnetic moment (PMM), everywhere in the BZ except at high-symmetry points such as $\mathrm{\Gamma }$, $R$, $X$, and $M$. The PAM and PMM are large along the chiral rotation axis and in the vicinity of the topological nodes. In this study, we also reveal that all the topological phonon modes are chiral. However, the reverse is not always true. Among other things, our finding of the coexistence of topological and chiral phonon modes in chiral RhGe not only deepens our understanding of the phonon behavior in the CoSi family but also opens pathways for developing advanced materials and devices.

We propose a mixed-configuration approximation based on single-band impurity solvers to efficiently study nonequilibrium multiorbital systems at moderate computational cost. In this work, we merge the approach with the so-called auxiliary master equation approach. As a benchmark, we first show that our approach reproduces the results of quantum Monte Carlo (QMC) for two-orbital impurity models at equilibrium with overall good accuracy, especially for nondegenerate orbitals. We then use our approach as an impurity solver for dynamical mean-field theory (DMFT) to address the case of a two-orbital, realistic layered structure, recovering the strong crystal-field-driven charge polarization observed by solving the DMFT self-consistent cycle with QMC, albeit slightly reduced. Finally, we address a prototype nonequilibrium setup by sandwiching this layer between metallic contacts subject to a bias voltage described by different chemical potentials. This simplified model demonstrates our method's potential to access nonequilibrium steady-state behavior of multiorbital, realistic materials. These findings provide a first-step basis for theoretical studies of nonequilibrium properties of multiorbital compounds directly in the real frequency domain.

Dissipation is traditionally regarded as a disruptive factor in quantum systems because it often leads to decoherence and delocalization. However, recent insights into engineered dissipation reveal that it can be tuned to facilitate various quantum effects, from state stabilization to phase transitions. In this work, we identify aperiodic dissipation as a mechanism for inducing steady-state localization, independent of disorder or a quasiperiodic potential in the Hamiltonian. This localization arises from long-range phase correlations introduced by a spatially varying dissipation phase parameter, which enables nontrivial interference in the steady state. By systematically comparing two classes of aperiodic dissipation (defined as commensurate and incommensurate cases), we conclude that both can lead to localization in the thermodynamic limit. Our analysis, based on coherence measures, purity, and participation ratio, reveals a direct link between eigenstate coherence and real-space localization, showing that dissipation can actively shape localization rather than simply causing decoherence. These findings highlight aperiodic dissipation as a viable approach to controlling localization in open quantum systems, potentially enabling new ways to manipulate quantum states and design dissipation-driven phases.

We analyze the quantum transport of charged fermionic particles in the tight-binding lattice connecting two particle reservoirs (leads). If the lead chemical potentials are different they create an electric field which tilts the lattice. We study the effect of this tilt on quantum transport in the presence of weak decoherence processes in the lattice. It is shown that a Landauer ballistic transport regime for a small tilt changes to a diffusive Esaki-Tsu transport regime for a larger tilt. The critical tilt for this crossover is determined by the condition that the Wannier-Stark localization length coincides with the length of the lattice.

Utilizing the established Bistritzer-MacDonald model for twisted bilayer graphene (tBLG), we theoretically investigate the non-Hermitian (NH) topological properties of this in the presence of nonreciprocal (NR) hopping on both layers and hexagonal boron nitride (hBN)-induced mass term incorporated only on the top layer of the tBLG system. It is well known that the hBN mass term breaks the $C_2$ symmetry of tBLG and gaps out the Dirac cones, inducing a valley-Hall insulating phase. However, when NR hopping is introduced, this system transits into a NH valley-Hall insulator. Our analysis reveals that in the chiral limit, the bandwidth of the system vanishes under NH effects for a wide range of twist angles. Such range can be visibly expanded as we enhance the degree of non-Hermiticity ($\beta$). At the magic angle, we observe that enhancement of $\beta$ inflates the robustness of the gapless Dirac points, requiring a progressively larger mass term to induce a gap in the NH tBLG system. Additionally, for a fixed NH parameter, we identify a range of twist angles where gap formation is significantly obstructed. To explore the topological aspects of the NH tBLG, we analyze the direct band gap in the moiré Brillouin zone (mBZ) and compute the Chern number for the NH system. We find that the corresponding topological phase transitions are associated with the corresponding direct band-gap closings in the mBZ.

Using a combined analysis from Poisson-Dirichlet and symmetry-breaking calculations as well as quantum Monte Carlo simulations, we examine the ordered phase and the thermal phase transition of the three-dimensional spin-1 quantum magnet on the simple cubic lattice with bilinear and biquadratic interactions and SU(3) internal symmetry. We obtain exact results for the order parameter distribution function that compare well to the quantum Monte Carlo data. Furthermore, based on a detailed finite-size analysis, we provide evidence that the thermal melting transition at the SU(3) point is either weakly first order in this system or, if continuous, it falls beyond the unitarity bounds of conformal field theory.

We evaluate the real-space second Chern number of four-dimensional Chern insulators using the kernel polynomial method. Our calculations are performed on a four-dimensional system with ${30}^4$ sites, and the numerical results agree well with theoretical expectations. Moreover, we show that the method is capable of capturing the disorder effects. This is evidenced by the phase diagram obtained for disordered systems, which agrees well with predictions from the self-consistent Born approximation. Furthermore, we extend the method to six dimensions and perform an exploratory real-space calculation of the third Chern number. Although finite-size effects prevent full quantization, the numerical results show qualitative agreement with theoretical expectations. The study represents a step forward in the real-space characterization of higher-dimensional topological phases.

Controllable particle flows play an important role in modern optics and photonics. Switching off photon flows using optical methods is challenging to realize due to the limited ways to control photon interactions. Here, we realize an exciton polariton condensate flow in a waveguide of a GaAs microcavity with a potential gradient by using a tight pumping spot. Polariton condensate flow along the waveguide can be periodically switched off and on globally by adding a second local small spot on the waveguide. Tuning the pumping density or position induces a pump intensity and position-dependent potential barrier modulating the phase of the condensate by a polariton-exciton interaction. This enables us to study the polariton condensation process in a waveguide by phase modulation, which could find important applications in integrated photonic circuits and chips.

It is well-known that a direct band gap may be opened in bilayer graphene via the application of a perpendicular electric field (bias). The bias and the chemical potential are controlled by electrostatic gating where the top and bottom gate voltages are tuned separately. The value of the band gap opened by the bias field is influenced by the self-screening of the bilayer graphene. The Hartree contribution to the self-screening is well-known in the literature, with Hartree screening significantly renormalizing the gap. In the present work we derive the Fock contribution to the self-screening and demonstrate that it is equally important and, in the low-density regime, even more important than the Hartree contribution. We calculate the Hartree-Fock screened band gap as a function of electron doping at zero temperature and also as a function of temperature at zero doping.

We theoretically investigate the thermoelectric properties (electronic contribution) of a normal-superconductor (NS) hybrid junction, where the normal region consists of magic-angle twisted bilayer graphene (MATBG). The superconducting region is characterized by a conventional $s$-wave superconductor closely proximitized to the MATBG. We compute various thermoelectric coefficients, including thermal conductance, thermopower, and the figure-of-merit ($zT$), using the scattering matrix formalism. These results are further supported by calculations based on a lattice-regularized version of the effective Hamiltonian. Additionally, we explore the impact of trigonal warping and valley polarization on the thermoelectric coefficients. Notably, we find a significant variation in $zT$ as a function of these parameters, reaching values as high as 2.5. Interestingly, we observe a violation of the Wiedemann-Franz law near the charge neutrality point with the superconducting correlation, indicating that MATBG electrons behave as slow Dirac fermions in this regime. This observation is further confirmed by the damped oscillatory behavior of the thermal conductance as a function of the barrier strength when an insulating barrier is modeled at the interface of the NS junction. Beyond theoretical insights, our findings suggest possibilities for thermoelectric applications using MATBG-based NS junctions.

We propose a straightforward and highly accurate method for extracting material parameters such as screening length, bandgap energy, exciton reduced mass, and the dielectric constant of the surrounding medium from experimental magnetoexciton energies available for monolayer transition metal dichalcogenides (TMDCs). Our approach relies on analytical formulations that allow us to calculate the screening length $r_0$ and bandgap energy $E_g$ directly from the experimental $s$-state exciton energies $E_{1s}, E_{2s}$, and $E_{3s}$. We also establish a relationship between the surrounding dielectric constant $\kappa$ and the exciton reduced mass $\mu$. This relationship simplifies the Schrödinger equation for a magnetoexciton in a TMDC monolayer, transforming it into a one-parameter equation that depends solely on the single material parameter $\mu$. Furthermore, we develop an analytical formula with high accuracy for magnetoexciton energies as a function of the exciton reduced mass: $E(B,\mu )$. Then, the inverse of this formula allows us to calculate the exciton reduced mass from experimental data on magnetoexciton energies. By applying this method, we extract key material parameters, $E_g, r_0, \mu$, and $\kappa$, from the magnetoexciton energies of monolayer TMDCs, including ${\mathrm{WSe}}_2, {\mathrm{WS}}_2, {\mathrm{MoSe}}_2$, and ${\mathrm{MoS}}_2$, encapsulated by hexagonal boron nitride (hBN) slabs in various current experiments. The material properties we retrieve complement and correct existing experimental and theoretical data. Additionally, we develop an analytical method for calculating diamagnetic coefficients and exciton radii with high accuracy compared to numerical calculations. Based on this method, we provide diamagnetic coefficients and exciton radii computed using the extracted material parameters.