It is well known that the proximity effect at superconductor/ferromagnet (S/F) interfaces produces damped oscillatory behavior of the Cooper-pair wave function within the ferromagnetic regions, which is analogous to the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductivity. It is often called the mesoscopic FFLO state and gives rise to $0-\pi$ transitions in S/F/S Josephson junctions. This paper offers an analysis of the proximity effect at interfaces between superconductors and magnetic van der Waals (vdW) bilayers. The specific feature of the proximity effect in the vdW bilayer systems is the presence of nonlocal Cooper pairs. We predict that the mesoscopic FFLO state formed by such pairs is sensitive to the difference between on-site energies of the monolayers composing the bilayer and, thus, can be controlled by applying a gating potential to one of the monolayers. This opens the possibility of implementing gate-controlled $0-\pi$ transitions in Josephson junctions through the magnetic vdW bilayer weak links.

The topological defects of Spin($n+1$) nematics in two spatial dimensions, known as disclinations, are characterized by the ${\pi }_1\left(\mathbb{R}{P}^n\right)={\text{Z}}_2$ homotopy group for $n\ge 2$. We argue that incompressible quantum liquids of disclinations can exist as stable low-temperature phases and host composite quasiparticles which combine a fractional amount of fundamental ${\mathrm{Z}}_2$ charge with a unit of topological charge. The fourfold topological ground state degeneracy on a torus admits a fermionic or semionic quasiparticle exchange statistics. The topological nontriviality of these states is visible in the existence of protected gapless edge modes. While the fermionic nematic and gapped ${\mathrm{Z}}_2$ spin liquids have equivalent topological orders, they are still thermodynamically distinct due to having different edge modes, in analogy to the topologically nontrivial and trivial states of quantum spin-Hall systems. The analysis proceeds by recasting the ${\mathrm{Z}}_2$ gauge theory of spin nematics as a continuum limit theory with a larger gauge structure. Nematic fractionalization parallels that of a quantum Hall liquid, but the large gauge symmetry restores the time-reversal symmetry and restricts the quasiparticle fusion rules and statistics. The conclusions from field theory analysis are complemented with the construction of plausible host microscopic models.

We construct a family of chiral symmetry-protected third-order topological insulators by stacking Su-Schrieffer-Heeger (SSH) chains and provide a unified topological characterization by a series of Bott indices. Our approach is informed by the analytical solution of corner states for the model Hamiltonians written as a summation of the extended SSH model along three orthogonal directions. By utilizing the generalized Pauli matrices, an enumeration of the constructed model Hamiltonians generates ten distinct models, including the well-studied three-dimensional Benalcazar-Bernevig-Hughes model. By performing a boundary projection analysis for the ten models, we find that certain surfaces and hinges of the systems can exhibit, respectively, nontrivial second-order and first-order topology in the phase of the third-order topological insulators. Furthermore, we analyze the phase diagram for one of the predicted models and reveal a rich set of topological phases, including the third-order topological insulators, second-order weak topological insulators, and second-order nodal semimetals.

The competition between the Kondo spin-screening effect and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in heavy-fermion systems drives the quantum phase transition (QPT) between the magnetically ordered and the heavy-Fermi-liquid ground states. Despite intensive investigations of heavy quasiparticles on the Kondo-screened side of the QPT and of their breakdown at the quantum critical point, the magnetically ordering side has not systematically been studied. Using terahertz time-domain spectroscopy, we report a suppression of the Kondo quasiparticle weight in ${\mathrm{CeCu}}_{6-x}{\mathrm{Au}}_x$ samples on the antiferromagnetic (AFM) side of the QPT at temperatures as much as two orders of magnitude above the Néel temperature $T_{\text{N}}$. With our systematic investigations into the high-temperature, paramagnetic region on the AFM side of the phase diagram of ${\mathrm{CeCu}}_{6-x}{\mathrm{Au}}_x$, i.e., with $x=0.2$, 0.3, and 0.5, we show that the suppression results from a quantum frustration effect induced by the temperature-independent RKKY interaction. Hence, our results emphasize that, in addition to critical fluctuations, the RKKY interaction may play an important role in the quantum-critical scenario.

Phases of I-III-$\mathrm{V}{\mathrm{I}}_2$ chalcopyrite compounds are attracting ever-increasing attention, particularly in the current era of the rise of functional materials. In this work we found that the phase transition of $\mathrm{AgIn}{\mathrm{Se}}_2$ can be triggered by high-pressure sintering from a tetragonal to a rhombohedral structure. The crystal structure, phase transition conditions, and stability of the high-pressure phase are thoroughly investigated, revealing the structural information, drawing the phase diagram, and improving the structural stability. Given the potential high thermoelectric performance in $\mathrm{AgIn}{\mathrm{Se}}_2$, we carry out the study of the electrical transport properties for the high-pressure phase. Compared to the intrinsic phase, the electrical conductivity and power factor increase by six orders of magnitude and 1000 times, respectively. The electronic structure by density functional theory calculations indicates that the abnormal electrical properties originate from the variation in cationic coordination number caused by the phase transition, which leads to the increased contribution of $5s$ orbitals of Ag and In atoms to the conduction-band minimum, largely reducing the band gap and motivating the carrier concentration. These findings provide a strategy for structural design and performance optimization of $\mathrm{AgIn}{\mathrm{Se}}_2$ manipulated by the phase transition.

Recent research on exciton polaritons (EPs) in two-dimensional semiconductors has garnered significant attention. Transition metal dichalcogenides, due to their exotic physical properties, hold great promise for applications in various fields, including Bose-Einstein condensation, nanophotonics, and quantum optics. In this work, using finite-element method calculations, we demonstrate a coupling regime transition induced multiple quasibound state in the continuum (Q-BIC) strong-coupling model in a permittivity-asymmetric tetramer metasurface system with $C_{4\mathrm{v}}$ symmetry that supports three high Q-factor resonance modes. A tungsten disulfide ($\mathrm{W}{\mathrm{S}}_2$) monolayer is positioned on the permittivity-asymmetric metasurface, enabling strong coupling between multiple strongly coupled Q-BICs and the $\mathrm{W}{\mathrm{S}}_2$ exciton, which can be modulated by adjusting the height and gaps within the tetramer. Interestingly, the resonances of the Q-BICs can form coupling regime transition induced hybridized EPs. Additionally, the coupling strength can be effectively controlled by manipulating the tetramer's gaps. This work represents the realization of EPs in a multiple Q-BIC permittivity-asymmetric system, and this coupling regime transition induced Q-BIC-EP permittivity-asymmetric system significantly reduces the mode volume, while simultaneously enhancing the Purcell effect and the photoluminescence efficiency. It offers promising pathways for practical device concepts in polaritonic applications and other fields of physical investigation, such as nanolasers, superfluidity, and quantum information technologies.

In this work, we use the local spin Chern marker (LSCM) recently introduced by Baù and Marrazzo [Phys. Rev. B 110, 054203 (2024)] to analyze the real-space ($\mathbf{r}$-space) topology of the ground-state electronic wave functions in a honeycomb structure described by three distinct models. The models considered here are characterized by strong Rashba spin-orbit interaction, which leads to nonconservation of the spin operator, i.e., $[\mathcal{H},{\widehat{s}}_z]\ne 0$. The three spin-orbit couplings associated with the topological aspects of the models are as follows: (1) standard Kane-Mele coupling, (2) sublattice-dependent Kane-Mele coupling, and (3) in-plane (${\widehat{s}}_y$) polarized Kane-Mele coupling. These couplings occur in graphene grown on suitable substrates and are relevant for modeling its van der Waals heterostructures. A particular topological phase diagram characterizes each of these spin-orbit interactions, and our calculations of LSCM, fully performed on $\mathbf{r}$ space, successfully capture its general features. We also performed a detailed analysis of the spectral properties of the energy and valence-projected spin-matrix eigenvalues, which shows that both exhibit a gap that protects the marker. To complement, we examine the effect of disorder and spatial inhomogeneities on the LSCM for the different lattice models addressed in our work. Our results expand the applicability of the spin Chern number method to a class of lattice Hamiltonians with experimental relevance and may contribute to future research on the real-space topology of realistic materials.

We investigate electron transport through a double dot Aharonov-Bohm interferometer coupled to a heat bath, which provides not only a dephasing source but also non-Markovian memory effects. The distribution of waiting times between subsequent electron transfers is utilized to analyze the unique non-Markovian dephasing dynamics, especially at short times. We show how the coherent oscillations in the weak system-bath coupling regime are washed out in the strong coupling limit, due to the dephasing during the propagation of the electrons through the double dot interferometer. Intriguingly, we find for an intermediate coupling strength that the non-Markovian properties of the system-bath coupling unambiguously give rise to a revival of the coherent oscillations in the waiting time distribution. By analyzing the corresponding moments, we furthermore demonstrate the unique advantages of the higher-order moments in revealing the non-Markovian characteristics.

We demonstrate that introducing altermagnetism on the surface of a weak topological insulator (TI) results in the emergence of a single massless Dirac fermion, exhibiting a parity anomaly. To explore the transport properties induced by this parity anomaly, we propose an effective two-dimensional (2D) lattice model to describe the weak TI surface. This model captures both the energy spectrum and spin texture of the weak TI surface while reducing computational complexity. We show that the weak TI surface hosts a half-integer chiral edge current under the influence of altermagnetism. Additionally, in the presence of decoherence, the Hall conductance attains a half-quantized value. Layer-resolved calculations from a 3D slab model further confirm that surface altermagnetism drives the surface Hall conductance to transition to $e^2/2h$, aligning with calculation from the 2D effective lattice model. Our findings establish a link between altermagnetism and quantum anomalies, positioning weak TIs as a potential platform for investigating the parity anomaly without a net magnetic moment.

Due to their immense representative power, neural network quantum states (NQS) have gained significant interest in current research. In recent advances in the field of NQS, it has been demonstrated that this approach can compete with state-of-the-art numerical techniques, making NQS a compelling alternative, in particular for the simulation of large, two-dimensional (2D) quantum systems. In this study, we show that recurrent neural network (RNN) wave functions can be employed to study systems relevant to current research in quantum many-body physics. Specifically, we employ a 2D tensorized gated RNN to explore the bosonic Hofstadter model with a variable local Hilbert space cutoff and long-range interactions. At first, we benchmark the RNN-NQS for the Hofstadter-Bose-Hubbard (HBH) Hamiltonian on a square lattice. We find that this method, despite the complexity of the wave function, is capable of efficiently identifying and representing most ground-state properties. Afterwards, we apply the method to an even more challenging model for current methods, namely, the Hofstadter model with long-range interactions. This model describes Rydberg-dressed atoms on a lattice subject to a synthetic magnetic field. We study systems of size up to $12\times 12$ sites and identify three different regimes by tuning the interaction range and the filling fraction $\nu$. In addition to phases known from the HBH model at short-range interaction, we observe bubble crystals and Wigner crystals for long-range interactions. Especially interesting is the evidence of a bubble crystal phase on a lattice, as this gives experiments a starting point for the search of clustered liquid phases, possibly hosting non-Abelian anyon excitations. In our work, we show that NQS are an efficient and reliable simulation method for quantum systems, which are the subject of current research. In particular, we demonstrate the ability of this method to simulate challenging systems with long-range interactions.

The interplay between magnetism and strong topological insulator gives rise to distinct new topological phases and various intriguing phenomena, attracting significant attention in recent years. However, magnetic effects in weak topological insulators remain largely unexplored. In this work, we systematically investigate the magnetic effect on thin films of weak topological insulators. We focus on ferromagnetic and antiferromagnetic effects, which have been extensively studied in strong topological insulators, as well as the recently highlighted altermagnetic effect. We reveal that the interplay between magnetism and weak topological insulators leads to a variety of Hall effects in the absence of an external magnetic field, including the metallic quantum anomalous Hall effect without chiral edge states, the quantum anomalous Hall effect with a higher Hall conductance plateau, the quantized layer Hall effect, the metallic half-quantized valleylike Hall effect, and a quantized valleylike Hall effect. This work provides valuable insights for exploring magnetic effect on weak topological insulators.

The disorder-induced quantum phase transition between superfluid and nonsuperfluid states of bosonic particles in one dimension is generally expected to be of the Berezinskii-Kosterlitz-Thouless (BKT) type. Here, we show that hard-core lattice bosons with power-law hopping decaying with distance as $1/r^{\alpha }$ with a finite integral over space—corresponding in spin language to an $XY$ model with power-law couplings—undergo a non-BKT continuous phase transition instead. We use exact quantum Monte Carlo methods to determine the phase diagram for different values of the exponent $\alpha$, focusing on the regime $\alpha >2$. We find that the scaling of the superfluid stiffness with the system size is scale invariant at the transition point for any $\alpha \le 3$—a behavior incompatible with the BKT scenario and typical of continuous phase transitions in higher dimension. By a scaling analysis near the transition point, we find that our data are consistent with a correlation length exponent satisfying the Harris bound $\nu \ge 2$ and demonstrate a universal behavior of disordered bosons in one dimension. For $\alpha >3$ our data are consistent with a BKT scenario where the liquid is pinned by infinitesimal disorder.

Experimentally realization of interlayer ferromagnetic (FM) coupling in antiferromagnetic (AFM) $\mathrm{MnB}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$ family of materials (MBTs) plays an important role for exploring many exotic quantum phenomena, such as (quantum) anomalous Hall effect and magnetic Weyl semimetal phase. Here, we propose electron doping to realize interlayer FM coupling in layered MBTs. The mechanism is based on that electron doping can drive the Bi $p$ orbitals of MBTs down towards the Fermi level, where the unfully Bi $p$ orbitals indirectly allows the Mn atoms between two adjacent MBT to open a channel of the same spin, which further leads to the interlayer FM coupling. Through first-principles calculations, we demonstrate that electron doping, including Li, Na, K, Ca, Al, and Ga dopants, can indeed induce interlayer AFM to FM phase transition in MBT bilayer, accompanied by semiconducting to metallic phase transition. Specifically, the K-doped MBT hosts the Curie temperature of 53 K, which is much higher than that of pristine MBT. Further topological identification shows that topological states below the Fermi levels are well preserved when atoms are doped on the surface of MBT, which can be observed by using angle-resolved photoemission spectroscopy. Our work highlights the approach toward realizing interlayer FM coupling and paves the way for further study of quantum phenomena in MBTs as well as their magnetic applications. It is worth noting that K atoms have been successfully doped in MBT.

Brillouin light scattering (BLS) spectroscopy is a powerful tool for detecting spin waves in magnetic thin films and nanostructures. Despite comprehensive access to spin-wave properties, BLS spectroscopy suffers from the limited wave number of detectable spin waves and the typically relatively low sensitivity. In this paper, we present the results of numerical simulations based on the recently developed analytical model describing plasmon-enhanced BLS. Effective susceptibility is defined for a single plasmonic nanoparticle in the shape of an ellipsoid of rotation, for the sandwiched plasmonic nanoparticles separated by a dielectric spacer, as well as for the array of plasmonic resonators on the surface of a magnetic film. It is shown that the eccentricity of the metal nanoparticles, describing their shape, plays a leading role in enhancing the BLS signal. The optimal conditions for BLS enhancement are numerically defined for gold and silver plasmon systems for photons of different energies. The presented results define the roadmap for the experimental realization of plasmon-enhanced BLS spectroscopy.

Intense femtosecond x-ray pulses produced by an x-ray free-electron laser can trigger irreversible structural transitions in crystalline solids. For instance, irradiation of diamond can lead to graphitization and, at higher deposited doses, to amorphization. Our Monte Carlo simulations of irradiated diamond under realistic experimental conditions demonstrate that triggering graphitization or other phase transitions with hard x-ray photons can be challenging due to the ballistic escape of photoelectrons out of the beam focus. The decisive parameter here is the photoelectron range in proportion to the focal beam size. For future experiments on x-ray-induced transitions, such dedicated simulations of ballistic transport preceding the beamtime will be necessary. They can predict experimental conditions under which the desired distribution of the absorbed x-ray dose in the irradiated solid can be achieved.

Research on two-dimensional van der Waals materials has demonstrated that the layer degree of freedom can significantly alter the physical properties of materials due to the substantial modification of bulk bands. Inspired by this concept, layered photonic systems have been proposed and realized, revealing phenomena absent in their monolayer counterparts. In this work, we experimentally investigate the band structures of bilayer valley photonic crystals. Two typical structures with different stacking configurations are experimentally imaged via the near-field scanning technology, exhibiting distinct bulk band structures. Furthermore, different topological edge modes induced by distinct topology are observed, revealing that the layer degree of freedom can be regarded as a pseudospin and offering further capabilities for controlling the flow of light. Our work not only elucidates the evolution of band structures from monolayer to bilayer topological systems but also provides an experimental platform for the further exploration of bilayer topological insulators.

The Lindblad master equation (LME) describing the Markovian dynamics of the quantum open system can be understood as the evolution of the effective non-Hermitian Hamiltonian balanced with random quantum jumps. Here we investigate the balance-breaking dynamics by partly eliminating jumps from postselection experiments. To describe this dynamics, a nonlinear Lindblad master equation (NLME) is derived from the quantum trajectory method. However, the NLME shows significant advantages in analytical analysis over the quantum trajectory method. Using the NLME, we classify the dynamics into two classes. In the trivial class, the process of reducing jumps is completely equivalent to weakening the coupling from the environment. In contrast, the nontrivial class presents more complex dynamics. We study a prototypical model within this class and demonstrate the existence of the postselected skin effect whose steady state is characterized by the accumulation of particles on one side. The steady-state distribution can be fitted by a scale-invariant tanh function which is different from the uniform distribution of LME. Furthermore, the NLME can give a reasonable framework for studying the interplay and competition between the non-Hermitian Hamiltonians and dissipative terms. We show this by capturing the characteristics of the trajectory-averaged entanglement entropy influenced by non-Hermitian skin effect and Zeno effect in the model of postselected skin effect.

We investigate the excitation spectra of a spin-1/2 antiferromagnetic Heisenberg trimer spin chain by employing a combination of numerical and theoretical techniques. Utilizing the Krylov-space correction-vector method in density matrix renormalization group (DMRG), we calculate both the direct and indirect resonant inelastic x-ray scattering (RIXS) spectra for the trimer spin chain. To interpret the observed features in the RIXS spectra, we perform a theoretical perturbative analysis to compute the energy dispersions, which are then utilized to determine the density of states (DOS) for both the single-particle and the two-particle excitation spectra. Our results show that the single-particle continua of the direct RIXS spectrum align with the energy levels observed in the DOS spectra of spinon, doublon, and quarton excitations. Furthermore, the two-particle continua are revealed in the indirect RIXS process, where all possible single-particle excitations combine to form the various two-particle excitations of the trimer spin chain. Based on our calculations, we propose the RIXS mechanism of generating the fractionalized (spinon) and collective (doublon and quarton) excitations in the trimer spin chain at both the $L$ edge and the $K$ edge, including discussing the interplay of these excitations in the RIXS spectrum for various trimer coupling strength. The computed energy range of the excitations suggest the possibility of experimental detection at both the $L$ edge and the $K$ edge within the current capabilities of RIXS instrumentation resolution.