Plasmonically induced transparency (PIT) is a physical phenomenon that mimes electromagnetically induced transparency in plasmonic systems. However, it is challenging to maintain its line shape with the presence of disorders or defects, mainly because it is highly susceptible to structural parameters. Herein, a two-dimensional graphene plasmonic system, which is composed of a few periods of vertically arranged graphene-nanoribbon (GNR) pairs coupled with a graphene waveguide, is proposed. By constructing GNRs to form bright and dark plasmon modes with topologically nontrivial phases, the optical response of the graphene waveguide system gives rise to robust PIT effects that exhibit an immunity to a certain degree of various parametric perturbations and imperfections. A three-level plasmonic system is demonstrated to explain the formation mechanism of the PIT effects, and the corresponding results agree well with the numerical ones. Combining topology with PIT helps to reduce the impact of parametric disorders and defects, which benefits the PIT devices with design freedom and higher stability.

Atomically thin materials based on transition-metal dichalcogenides and graphene offer a promising avenue for unlocking the mechanisms underlying the spin Hall effect (SHE) in heterointerfaces. Here we develop a microscopic theory of the SHE for twisted van der Waals heterostructures that fully incorporates twisting and disorder effects and illustrate the critical role of symmetry breaking in the generation of spin Hall currents. We find that an accurate treatment of vertex corrections leads to a qualitatively and quantitatively different SHE than that obtained from the popular $i\eta$ and ladder approximations. A pronounced oscillatory behavior of skew-scattering processes with twist angle $\theta$ is predicted, reflecting a nontrivial interplay of Rashba and valley-Zeeman effects and yields a vanishing SHE for $\theta ={30}^{\circ }$ and, for graphene-${\mathrm{WSe}}_2$ heterostructures, an optimal SHE for $\theta \approx {17}^{\circ }$. Our findings reveal disorder and broken symmetries as important knobs to optimize interfacial SHEs.

Addressing high-dimensional partial differential equations to derive effective actions within the functional renormalization group is formidable, especially when considering various field configurations, including inhomogeneous states, even on lattices. We leverage physics-informed neural networks (PINNs) as a state-of-the-art machine-learning method for solving high-dimensional partial differential equations to overcome this challenge. In a zero-dimensional $\mathrm{O}\left(N\right)$ model, we numerically demonstrate the construction of an effective action on an $N$-dimensional configuration space, extending up to $N=100$. Our results underscore the effectiveness of PINN approximation, even in scenarios lacking small parameters such as a small coupling.

Adaptive quantum circuits, in which unitary operations, measurements, and feedback are used to steer quantum many-body systems, provide an exciting opportunity to generate interesting dynamical steady states. We introduce an adaptive quantum dynamics with continuous symmetry where unitary operations, measurements, and local unitary feedback are used to drive ordering. In this setting, we find a pure steady state hosting symmetry-breaking order, which is the ground state of a gapless, local Hamiltonian. We explore the dynamical properties of the approach to this steady state. We find that this steady-state order is fragile to perturbations, even those that respect the continuous symmetry.

We investigated the behavior of non-Hermitian bosonic gases with Hubbard interactions in one-dimensional (1D) zigzag optical lattices through the calculation of dynamic response functions. Our findings showed the existence of a non-Hermitian quantum phase transition that is dependent on the pseudo-Hermitian symmetry. The system tends to exhibit a superfluid phase when subjected to weak dissipation. While under strong dissipation, the pseudo-Hermitian symmetry of the system is partially broken, leading to a transition toward a normal liquid phase. As the dissipation increases beyond the critical threshold, the pseudo-Hermitian symmetry is completely broken, resulting in a Mott-insulator phase. We propose an experimental setup using 1D zigzag optical lattices containing two-electron atoms to realize this system. In this paper, we emphasize the key role of non-Hermiticity in quantum phase transitions and offer a theoretical framework as well as experimental methods for understanding the behavior of dissipative quantum systems, implicating significant development of quantum devices and technologies.

By circumventing the difficulty of obtaining exact string state solutions to Bethe ansatz equations, we devise a truncated string state space approach for investigating spin dynamics in a nonintegrable spin-$\frac{1}{2}$ Heisenberg chain subjected to a staggered field at various magnetizations. The obtained dynamical spectra reveal a series of elastic peaks at integer multiples of the ordering wave vector $Q$, indicating the presence of multi-$Q$ Bethe string states within the ground state. The spectrum exhibits a separation between different string continua as the strength of the staggered field increases at low magnetization, reflecting the confinement of the Bethe strings. This approach provides a unified string-state-based framework for understanding spin dynamics in low-dimensional nonintegrable Heisenberg models, which has a successful application to observations across various phases of the quasi-one-dimensional antiferromagnet ${\mathrm{YbAlO}}_3$.

Finite-momentum pairing in a Pauli-limited spin-singlet superconductor arises from the pair-breaking effects of an external Zeeman field, a mechanism which is not applicable in odd-parity spin-triplet superconductors. However, in multiorbital systems, the relevant bands originating from different orbitals are usually separated in momentum space, implying that orbital-singlet pairing is a natural candidate for a finite-momentum pairing state. We show that finite-momentum pairing arises in even-parity orbital-singlet spin-triplet superconductors via the combination of orbitally nontrivial kinetic terms and Hund's coupling. The finite-momentum pairing is then suppressed with an increasing spin-orbit coupling, stabilizing a uniform pseudospin-singlet pairing. We also examine the effects of the magnetic field and find field-induced superconductivity at large fields. We apply these findings to the multiorbital superconductor with spin-orbit coupling, ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, and show that a finite-momentum pseudospin-singlet state appears between the uniform pairing and normal states. Future directions of inquiry relating to our findings are also discussed.

This paper is concerned with ab initio crystal structure relaxation under a fixed unit cell volume, which is a step in calculating the static equations of state and forms the basis of thermodynamic property calculations for materials. The task can be formulated as an energy minimization with a determinant constraint. Widely used line minimization-based methods (e.g., conjugate gradient method) lack both efficiency and convergence guarantees due to the nonconvex nature of the determinant constraint as well as the significant differences in the curvatures of the potential energy surface with respect to atomic and lattice components. To this end, we propose a projected gradient descent algorithm named PANBB. It is equipped with (i) search direction projections for lattice vectors, (ii) distinct curvature-aware initial trial step sizes for atomic and lattice updates, and (iii) a nonrestrictive line minimization criterion as the stopping rule for the inner loop. It can be proved that PANBB favors theoretical convergence to equilibrium states. Across a benchmark set containing 223 structures from various categories, PANBB achieves average speedup factors of approximately 1.41 and 1.45 over the conjugate gradient method and direct inversion in the iterative subspace implemented in off-the-shelf simulation software, respectively. Moreover, it normally converges on all the systems, manifesting its robustness. As an application, we calculate the static equations of state for the high-entropy alloy AlCoCrFeNi, which remains elusive owing to 160 atoms representing both chemical and magnetic disorder and the strong local lattice distortion. The results are consistent with the previous calculations and are further validated by experimental thermodynamic data.

Determining the doping level in high-temperature cuprate superconductors is crucial for understanding the origin of superconductivity in these materials and for unlocking their full potential. However, accurately determining the doping level remains a significant challenge due to a complex interplay of factors and limitations in various measurement techniques. In particular, in ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CuO}}_{6+\delta }$ and ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_{8+\delta }$, where the mobile carriers are introduced by nonstoichiometric oxygen $\delta$, the determination has been extremely problematic. Here, we study the doping dependence of the electronic structure of these materials in angle-resolved photoemission and find that both the doping level $p$ and the superconducting transition temperature $T_c$ can be precisely determined from the binding energy of the Bi $5d$ core levels. The measurements can be performed at room temperature, enabling the determination of $p$ and $T_c$ without cooling the samples. This should be very helpful for further studies of these materials.

The adiabatic connection integrand interpolation (ACII) method represents a general path for calculating correlation energies in electronic systems within the density functional theory. ACII functionals include both exact-exchange and the second-order correlation energy, as well as an interpolating function toward the strictly correlated electron (SCE) regime. Several interpolating functions have been proposed in the last years targeting different properties, yet an accurate ACII approach with broad applicability is still missing. Recently, we have proposed an ACII functional that was made accurate for the three-dimensional (3D) uniform electron gas as well as for model metal clusters. In this paper we present an ACII functional (named genISI2), which is very accurate for both three-dimensional (3D) and two-dimensional (2D) uniform electron gases and for the quasi-2D infinite-barrier model, where most of the exchange-correlation functionals fail badly, as well as for strongly correlated two-electrons systems. Using the exact-exchange Kohn-Sham orbitals, we have also assessed the genISI2 for various molecular systems, showing a superior performance with respect to the other ACII methods for total energies, atomization energies, and ionization potentials. The genISI2 functional can thus find application in a broad range of systems and properties.

We study the quantum dynamics of interstitials and vacancies in a two-dimensional Wigner crystal (WC) using a semiclassical instanton method that is asymptotically exact at low density, i.e., in the $r_s\to \infty$ limit. The dynamics of these point defects mediates magnetism with much higher-energy scales than the exchange energies of the pure WC. Via exact diagonalization of the derived effective Hamiltonians in the single-defect sectors, we find the dynamical corrections to the defect energies. The resulting expression for the interstitial energy extrapolates to 0 at $r_s=r_{\mathrm{mit}}\approx 70$ (at $r_s\approx 30$ for a vacancy), suggestive of a self-doping instability to a partially melted WC for some range of $r_s$ below $r_{\mathrm{mit}}$. We thus propose a “metallic electron crystal” phase of the two-dimensional electron gas at intermediate densities between a low-density insulating WC and a high-density Fermi fluid.

In two-dimensional van der Waals (vdW) layered materials, application of pressure often induces a giant lattice collapse, which can subsequently drive an associated Mott transition. Here, we investigate room-temperature layer-dependent insulator-metal transition (IMT) and probable spin-crossover in vdW magnet, ${\mathrm{FePS}}_3$, under high-pressure using micro-Raman scattering. Experimentally obtained spectra, in agreement with the computed Raman modes, indicate evidence of IMT of ${\mathrm{FePS}}_3$ started with a thickness-dependent critical pressure ($P_c$) which reduces to 1.5 GPa in trilayer flakes compared with 10.8 GPa for the bulk counterpart. Using a phenomenological model, we argue that strong structural anisotropy in few-layer flakes enhances the in-plane strain under applied pressure and is, therefore, ultimately responsible for reducing the critical pressure for the IMT with decreasing layer numbers. Reduction of the critical pressure for phase transition in vdW magnets to 1–2 GPa marks the possibility of using intercalated few-layers in the field-effect transistor device architecture, and thereby, avoiding the conventional use of the diamond anvil cell.

We investigate the photonic spin Hall effect (PSHE) of light beams reflected from surfaces of various two-dimensional crystalline structures while considering their associated time-reversal $\mathcal{T}$ and inversion $\mathcal{I}$ symmetries. Using the modified Haldane model Hamiltonian with tunable parameters as a generic system, we explore longitudinal and transverse spin separations of the reflected beam in both topologically nontrivial and trivial systems. The PSHE observed in these materials is attributed to their topology. Topological phase transitions in buckled Xene monolayer materials are demonstrated through the PSHE, showing the manipulation of spin-orbit coupling and external electric fields. Moreover, we investigate spatial shifts in the PSHE of monolayer transition metal dichalcogenides, suggesting that the spin and valley degrees of freedom of charge carriers provide a promising avenue to manipulate the PSHE in both classes of these materials. The study suggests that the PSHE in Haldane model materials can serve as a metrological tool for characterizing topological phase transitions through quantum weak value measurement techniques.

The emergence of gapless surface states, known as Fermi arcs (FAs), is one of the unique properties of the novel topological Weyl semimetal (WSM). However, extracting the signatures of FAs from the bulk states has always been a challenge as both of them are gapless in nature and connected to each other. We capture the signatures of FAs via transport in an inversion symmetry broken WSM. We study the band structure and the properties of FAs such as shape, and spin polarization considering slab and nanowire (NW) geometry, and then compute the two-terminal conductance in WSM NWs in terms of the scattering coefficients within the Landauer formalism. We find the FA-mediated conductance to be quantized in units of $2e^2/h$. We extend our study to transport in the WSM/Weyl superconductor NW hybrid junction using the Blonder-Tinkham-Klapwijk formalism. We show that due to the intricate spin textures, the signatures of the FAs can be captured via the Andreev reflection process. We also show that our results of conductance are robust against delta-correlated quenched disorder and thus enhance the experimental feasibility.

We derive selection rules in optical absorption and Raman scattering spectra that can determine the parity of pairing order parameters under inversion symmetry in two classes of clean superconductors: (1) chiral superconductors with strong spin-orbit couplings and (ii) singlet superconductors with negligible spin-orbit couplings. Experimentally, the inversion parity of pair wave functions can be determined by comparing the “optical gap” ${\mathrm{\Delta }}_{\text{op}}$ in Raman and optical spectroscopy and the “thermodynamic gap” $2\mathrm{\Delta }$ in specific heat measurements, and the selection rules apply when ${\mathrm{\Delta }}_{\text{op}}>2\mathrm{\Delta }$. We demonstrate the selection rules for superconductivity in models of (1) doped Weyl semimetals and (2) doped graphene. Our derivation is based on the relation between pairing symmetry and the fermion projective symmetry group of a superconductor. We further derive similar selection rules for two-dimensional superconductors with twofold rotational symmetry and discuss how they apply to the superconducting state in magic-angle twisted bilayer graphene.

Neural-network quantum states (NQSs), variationally optimized by combining traditional methods and deep learning techniques, is a new way to find quantum many-body ground states and has gradually become a competitor of traditional variational methods. However, there are still some difficulties in the optimization of NQSs, such as local minima, slow convergence, and sign structure optimization. Here, we split a quantum many-body variational wave function into a multiplication of a real-valued amplitude neural network and a sign structure, and focus on the optimization of the amplitude network while keeping the sign structure fixed. The amplitude network is a convolutional neural network (CNN) with residual blocks, namely a residual network (ResNet). Our method is tested on three typical quantum many-body systems. The obtained ground state energies are better than or comparable to those from traditional variational Monte Carlo methods and density matrix renormalization group. Surprisingly, for the frustrated Heisenberg $J_1\text{−}{J}_2$ model, our results are better than those of the complex-valued CNN in the literature, implying that the sign structure of the complex-valued NQS is difficult to optimize. We will study the optimization of the sign structure of NQSs in the future.

Antiferromagnetic (AFM) semiconductor ${\mathrm{MnS}}_2$ possesses both high-spin and low-spin magnetic phases that can be reversibly switched by applying pressure. With increasing pressure, the high-spin state undergoes pressure-induced metallization before transforming into a low-spin configuration, which is then closely followed by a volume collapse and structural transition. We show that the pressure-driven band inversion is in fact topological, resulting in an antiferromagnetic ${\mathbb{Z}}_2$ topological metal (Z2AFTM) phase with a small gap and a Weyl metal phase at higher pressures, both of which precede the spin-state crossover and volume collapse. In the Z2AFTM phase, the magnetic order results in a doubling of the periodic unit cell, and the resulting folding of the Brillouin zone leads to a ${\mathbb{Z}}_2$ topological invariant protected by the persisting combined time-reversal and half-translation symmetries. Such a topological phase was proposed theoretically by Mong et al. [Phys. Rev. B 81, 245209 (2010)] in 2010 for a system with AFM order on a fcc lattice, which until now has not been found in the pool of real materials. ${\mathrm{MnS}}_2$ represents a realization of this original proposal through AFM order on the Mn fcc sublattice. A rich phase diagram of topological and magnetic phases tunable by pressure establishes ${\mathrm{MnS}}_2$ as a candidate material for exploring magnetic topological phase transitions and for potential applications in AFM spintronics.

We comparatively study three of the most useful quantum information tools to detect quantum critical points (QCPs) when only finite temperature data are available. We investigate quantitatively how the quantum discord, the quantum-teleportation-based QCP detectors, and the quantum coherence spectrum pinpoint the QCPs of several spin-$1/2$ chains. We work in the thermodynamic limit (infinite number of spins) and with the spin chains in equilibrium with a thermal reservoir at temperature $T$. The models here studied are the XXZ model with and without an external longitudinal magnetic field, the Ising transverse model, and the XY model subjected to an external transverse magnetic field.