We propose a method to directly probe bulk topological quantum numbers in topological matter by measuring the momentum-space single-particle spectral function (SPSF). Angle-resolved photoemission spectroscopy (ARPES) can detect SPSF and is often used to determine the bulk band structure of quantum materials. Here, we show that while one part of the momentum-space SPSF gives band structure, it also contains the knowledge of winding and Chern numbers of various topological materials. For this, we derive SPSF in different models of topological systems, such as the Kitaev model of topological superconductors, the long-range Su-Schrieffer-Heeger model, the Qi-Wu-Zhang model, the Haldane model on a hexagonal lattice, and a four-band model that is a physical realization of the Kitaev chain, and we explain how to extract the winding or Chern numbers in different topological phases from the SPSF. Such information from SPSF seems experimentally accessible due to the recent advancement of ARPES and scanning tunneling spectroscopy techniques. While the detection of bulk topological quantum numbers using the SPSF works well for one-dimensional systems, it has certain limitations for higher-dimensional systems, where it must be complementary with another measurement to ensure the matter under investigation is topological, i.e., having a nonzero Chern number.

Exploring the spectral properties of non-Hermitian systems presents a substantial theoretical challenge due to the presence of a complex eigenvalue spectrum. Singular values for such systems are inherently real and non-negative, and the techniques used for Hermitian systems can be used with ease. As a prototypical example of such systems, we investigate the singular-value spectrum of a non-Hermitian extension of the sparse Sachdev-Ye-Kitaev (SYK) model, a solvable toy model of quantum chaos and quantum gravity with significant interest in digital quantum simulation. Our findings reveal a congruence between the statistics of singular values and those of the analogous Hermitian Gaussian ensembles. An increase in sparsity results in the model deviating from its chaotic behavior, a phenomenon precisely captured by both short- and long-range correlations in the singular-value spectrum. These findings indicate the existence of a critical sparsity threshold, beyond which the chaotic nature of the model breaks down, suggesting a potential collapse of holographic duality in such systems.

Krylov space methods provide an efficient framework for analyzing the static and dynamical aspects of quantum systems, with tridiagonal matrices playing a key role. Despite their importance, the behavior of such matrices from chaotic to integrable states, transitioning through an intermediate phase, remains unexplored. We aim to fill this gap by considering the properties of the tridiagonal matrix elements and the associated basis vectors for appropriate random matrix ensembles. We utilize the Rosenzweig-Porter model as our primary example, which hosts a fractal phase in addition to the ergodic and localized regimes. We discuss the characteristics of the matrix elements and basis vectors across these three (ergodic, fractal, and localized) regimes and introduce Krylov space tools to identify the transition points. The exact expressions of the Lanczos coefficients of such tridiagonal matrices are provided in terms of $q$-logarithmic function across the full parameter regime. The numerical results are corroborated with analytical reasoning for certain features of the Krylov spectra. Additionally, we investigate the Krylov state (spread) complexity within these regimes, showcasing the efficacy of our methods in pinpointing these transitions.

A longstanding problem in time-dependent density functional theory has been the absence of a functional able to capture excitonic physics under laser pump conditions. Here we introduce a scheme of coupled Kohn-Sham and Proca equations in a pump-probe setup that we show (i) produces linear-response excitonic effects in the weak pump regime in excellent agreement with experiment, but also (ii) captures excitonic physics in the highly nonlinear regime of ultrafast strong laser pumping. In particular ”bleaching” (i.e., reduction) of the excitonic weight and the appearance of excitonic side bands is demonstrated. The approach is a procedural functional—the Kohn-Sham and Proca equations are simultaneously time propagated—allowing the straightforward inclusion of, for example, lattice and spin degrees of freedom into excitonic physics. The functional is shown to have universal applicability to a wide range of materials, and we also establish a relation between the parameters used in the functional and the exciton Bohr radii of the materials.

Recently, robust superconductivity has been independently reported in twisted ${\mathrm{WSe}}_2$ bilayers by two separate groups [Y. Xia et al., arXiv:2405.14784; Y. Guo et al., Nature (London) 637, 839 (2025)]. In light of this, we explore the possibility of a universal superconducting pairing mechanism in twisted ${\mathrm{WSe}}_2$ bilayers. Using a continuum band structure and a phenomenological boson-mediated effective electron-electron attraction, we find that intervalley intralayer pairing predominates over interlayer pairing. Notably, despite very different experimental conditions, both twisted ${\mathrm{WSe}}_2$ samples exhibit a comparable effective attraction strength for superconductivity. This consistency in the two experiments suggests that the dominant pairing glue is likely independent of the twist angle and layer polarization, pointing to a universal underlying boson-induced pairing mechanism. We speculate on the possible mechanisms in the discussion.

The self-diffusion process in a dense liquid is influenced by collective particle movements. Extensive molecular dynamics simulations for liquid aluminium and rubidium evidence a crossover in the diffusion coefficient at about 1.4 times the melting temperature $T_m$, indicating a profound change in the diffusion mechanism. The corresponding velocity autocorrelation functions demonstrate a decrease of the cage effect with a gradual set in of a power-law decay, they celebrate long time tail. This behavior is caused by a competition of density fluctuations near the melting point with vortex-type particle patterns from transverse currents in the hot fluid. The investigation of the velocity autocorrelation function evidences a gradual transition in dynamics with rising temperature. The competition between these two collective particle movements, one hindering and one enhancing the diffusion process, leads to a non-Arrhenius-type behavior of the diffusion coefficient around $1.4T_m$, which signals the transition from a dense to a fluidlike liquid dynamics in the potential energy landscape picture.

The quantum geometric tensor has established itself as a general framework for the analysis and detection of equilibrium phase transitions in isolated quantum systems. We propose a generalization of the quantum geometric tensor, which offers a universal approach to studying phase transitions in non-Hermitian quantum systems. Our generalization is based on the concept of the generator of adiabatic transformations and can be applied to systems described by either a Liouvillian superoperator or by an effective non-Hermitian Hamiltonian. We illustrate the proposed method by analyzing the non-Hermitian Su-Schrieffer-Heeger model and a generic quasifree dissipative fermionic system with a quadratic Liouvillian. Our findings reveal that this method effectively identifies phase transitions across all examined models, providing a universal tool for investigating general non-Hermitian systems.

An important question of quantum information is to characterize genuinely quantum (beyond-Clifford) resources necessary for universal quantum computing. Here, we use the Pauli spectrum to quantify how “magic,” beyond Clifford, typical many-qubit states are. We first present a phenomenological picture of the Pauli spectrum based on quantum typicality, and then we confirm it for Haar random states. We then introduce filtered stabilizer entropy, a magic measure that can resolve the difference between typical and atypical states. We proceed with the numerical study of the Pauli spectrum of states created by random circuits as well as for eigenstates of chaotic Hamiltonians. We find that in both cases, the Pauli spectrum approaches the one of Haar random states, up to exponentially suppressed tails. We discuss how the Pauli spectrum changes when ergodicity is broken due to disorder. Our results underscore the difference between typical and atypical states from the point of view of quantum information.

Coupled-magnon systems provide unique avenues for information exchange and energy transport in spintronic devices. The parity symmetry of these systems plays a crucial role in the introduction of magnon-magnon coupling. In this study, we break the parity symmetry by stacking different ferromagnetic layers in synthetic antiferromagnets CoZr/Ru/FeNi. This results in the hybridization between acoustic-type and optical-type magnons, forming an anticrossing gap. This gap signifies the presence of anisotropic magnon-magnon coupling driven by uniaxial magnetic anisotropy. Additional sputtering of IrMn on the FeNi sublayer results in robust unidirectional magnon hybridization. Both experimental and theoretical analyses indicate that the breaking of parity symmetry and coupling strength are well described by the angle between the total magnetization and the applied in-plane magnetic field qualitatively. The exchange bias in FeNi induced by IrMn can further enhance or suppress this symmetry breaking, transitioning the anisotropic coupling from twofold to unidirectional. This readily adjustable magnon hybridization presents promising opportunities for advancing unidirectional energy and information transfer in magnonic technologies.

We discuss the magnetic ground state and properties of a frustrated two-dimensional classical Heisenberg model of interacting hexagonal clusters of spins. The energy of the ground states is found exactly for arbitrary values of $J_1$ (intracluster couplings) and $J_2$ (intercluster couplings). Our main results concern a frustrated region of the phase diagram, where we show that the set of ground states has a degeneracy larger than that due to global rotation symmetry. Furthermore, the ground state manifold does not have a fixed total magnetization: there is a range of allowed values. At finite temperature, our Monte Carlo simulations show that the entropy selects the most probable value of the total magnetization, while the histogram of the Monte Carlo time series is nontrivial. This model is a first step towards modeling properties of a class of frustrated magnetic structures composed of coupled spin clusters.

Exploiting the spin-valley degree of freedom of electrons in materials is a promising avenue for energy-efficient information storage and quantum computing. A key challenge in utilizing spin-valley polarization is the realization of spin-valley locking in bulk systems. Here we report a comprehensive study of the noncentrosymmetric bulk misfit compound ${\left(\mathrm{PbS}\right)}_{1.13}\left({\mathrm{TaS}}_2\right)$, showing a strong spin-valley locking. Our investigation reveals Ising superconductivity with a transition temperature of 3.14 K, closely matching that of a monolayer of ${\mathrm{TaS}}_2$. Notably, the absence of charge density wave signatures in transport measurements suggests that the PbS layers primarily act as spacers between the dichalcogenide monolayers. This is further supported by angle-resolved photoemission spectroscopy (ARPES), which shows negligible interlayer coupling, a lack of dispersion along the $k_{\perp }$ direction, and significant charge transfer from the PbS to the ${\mathrm{TaS}}_2$ layers. Spin-resolved ARPES shows strong spin-valley locking of the electronic bands. Muon spin rotation experiments conducted in the vortex phase reveal an isotropic superconducting gap. However, the temperature dependence of the upper critical field and low-temperature specific-heat measurements suggest the possibility of multigap superconductivity. These findings underscore the potential of misfit compounds as robust platforms for both realizing and utilizing spin-valley locking in bulk materials, as well as exploring proximity effects in two-dimensional structures.

With the development of ferroelectric memories, it is becoming increasingly important to understand the ferroelectric switching behaviors at small applied electric fields. In this paper we use discretized phase-field models to systematically investigate the intrinsic threshold electric field (TEF) to drive flat ${180}^{\circ }$ and ${90}^{\circ }$ domain walls (DWs), which cannot be captured by continuum models. The results show that this TEF increases as the ratio of DW width to unit-cell size decreases, and it becomes significant if the DW width is thinner than two unit cells. The results are qualitatively consistent with existing first-principles studies and cryogenic experiments. In addition, this work proposes a conceptual model to explain the activation electric field (AEF) observed in experiments at room temperature. This work improves the understanding of DW motion kinetics at small applied fields and shows that the mesh size and orientation are both important for the phase-field modeling of the above process.

We develop and validate a lattice dynamics framework to include anharmonic effects in the calculation of mode-level phonon heat capacities. To capture anharmonicity, the phonons are renormalized using a temperature-dependent effective potential and a proposed approach based on instantaneous normal modes. Ground-truth total heat capacities are obtained from molecular dynamics simulations. For Lennard-Jones argon (Stillinger-Weber silicon), the deviation of the potential energy contribution to the total heat capacity from the harmonic Dulong-Petit law is $-12\%$ ($+16\%$) at the highest studied temperature of 80 K (1300 K). The mode heat capacities from the lattice dynamics calculations are summed and compared with the ground-truth total heat capacity. For all temperatures considered, the instantaneous normal mode approach gives the best prediction for Lennard-Jones argon (within 1.1%), while for Stillinger-Weber silicon the temperature-dependent effective potential is best (within 0.7%). The Lennard-Jones argon mode heat capacities decrease with increasing frequency and are impacted by the effect of anharmonicity on the mode's self energy and its interactions with other modes. In Stillinger-Weber silicon, the acoustic mode heat capacities increase by up to 30% relative to the Dulong-Petit law, with these deviations driven by the interactions between modes. The proposed calculation framework will improve high-temperature thermal conductivity calculations, where the heat capacity is generally assumed to take on the harmonic value from the Dulong-Petit law.

The phonon transport mechanisms and the anomalous temperature-dependent lattice thermal conductivities (${\kappa }_{\mathrm{L}}$) in Ag-based argyrodites have not been fully understood. Herein, we systematically study the phonon thermal transport of five Ag-based crystalline argyrodites ${\mathrm{Ag}}_7{\mathrm{PS}}_6, {\mathrm{Ag}}_7{\mathrm{AsS}}_6, {\mathrm{Ag}}_8{\mathrm{SnS}}_6, {\mathrm{Ag}}_8{\mathrm{GeS}}_6$, and ${\mathrm{Ag}}_9{\mathrm{GaS}}_6$ utilizing perturbation theory and the unified theory thermal transport model. Our results show that, as the complexity of the unit cell increases, the proportion of the population terms declines while the coherence contributions become more significant, leading to the relatively weak temperature-dependent ${\kappa }_{\mathrm{L}}$ of ${\mathrm{Ag}}_7{\mathrm{PS}}_6$ and ${\mathrm{Ag}}_7{\mathrm{AsS}}_6$, while the more complex crystalline argyrodites, ${\mathrm{Ag}}_8{\mathrm{SnS}}_6, {\mathrm{Ag}}_8{\mathrm{GeS}}_6$, and ${\mathrm{Ag}}_9{\mathrm{GaS}}_6$, exhibiting a glass-like behavior in their temperature dependence of ${\kappa }_{\mathrm{L}}$. We attribute the positive temperature-dependent and ultralow ${\kappa }_{\mathrm{L}}$ of ${\mathrm{Ag}}_8{\mathrm{SnS}}_6, {\mathrm{Ag}}_8{\mathrm{GeS}}_6$, and ${\mathrm{Ag}}_9{\mathrm{GaS}}_6$ to the dominance of wavelike phonons and the strong phonon broadening. Furthermore, using laser flash measurements and the homogeneous nonequilibrium molecular dynamics simulations based on accurate machine learning neuroevolution potentials, we provide further evidence for the glass-like temperature-dependent ${\kappa }_{\mathrm{L}}$ of ${\mathrm{Ag}}_8{\mathrm{SnS}}_6$ and ${\mathrm{Ag}}_8{\mathrm{GeS}}_6$.

One of the simplest and least resource-intensive methods to suppress decoherence for qubit operations, namely, dynamical decoupling (DD), is investigated for a broad range of realistic noise sources with time-retarded feedback. By way of example, the Carr-Purcell-Meiboom-Gill sequence is analyzed in a numerically rigorous manner accounting also for correlations between qubits and environments. Since experimentally noise sources are characterized through spectral densities, we adopt the spin-boson model as a suitable framework to describe the qubit dynamics under DD for a given spectral density $J\left(\omega \right)\propto {\omega }^s$. Motivated by the situation for superconducting qubits, the spectral exponent $s$ is varied from $s=1$ (Ohmic bath) to a substantially small value $0<s\ll 1$ (deep sub-Ohmic bath), in order to investigate the impact of time-nonlocal back action on DD performances for enhanced coherence times. As reference to the DD schemes, dynamics of a single qubit subject to Ramsey sequences without any pules and Hahn echo sequences are also investigated.