Eigenstates of quantum many-body systems are often used to define phases of matter in and out of equilibrium; however, experimentally accessing highly excited eigenstates is a challenging task, calling for alternative strategies to dynamically probe nonequilibrium phases. In this work, we characterize the dynamical properties of a disordered spin chain, focusing on the spin-glass regime. Using tensor-network simulations, we observe oscillatory behavior of local expectation values and bipartite entanglement entropy. We explain these oscillations deep in the many-body localized spin-glass regime via a simple theoretical model. From perturbation theory, we predict the timescales up to which our analytical description is valid and confirm it with numerical simulations. Finally, we study the correlation length dynamics, which, after a long-time plateau, resume growing in line with renormalization group (RG) expectations. Our work suggests that RG predictions can be quantitatively tested against numerical simulations and experiments, potentially enabling microscopic descriptions of dynamical phases in large systems.

Magnon-magnon coupling can be utilized to develop highly efficient information transmission and processing devices, such as spin-wave-based devices. Moreover, it is crucial in quantum information technology, particularly in facilitating interactions and information transfer between quantum bits. In this study, we reported the electric field-triggered magnon-magnon coupling in CoZr/Ta/CoZr/$\mathrm{Pb}\left({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}\right){\mathrm{O}}_{3-0.29}\mathrm{PbTi}{\mathrm{O}}_3$ sandwich-structured multilayer film. It maintains a uniform precession ferromagnetic resonance mode under an unpolarized state and demonstrates magnon-magnon coupling under an electric field of −6.25 kV/cm. The changes in effective damping of CoZr (bottom) are attributed to the magnon-driven spin screening effect (it will affect the spin-polarized charges at the ferromagnetic/ferroelectric interface to be distributed in a spiral pattern) induced by ferroelectric polarization, which breaks the parity-time symmetry within the sandwich structure, facilitating electric-field-triggered magnon-magnon coupling. This discovery opens a pathway for achieving magnon-magnon coupling by direct ferromagnetic exchange interactions.

Topological insulators, which are insulative in bulk while conductive on surfaces, are protected by the nontrivial topology of electronic band structures. This concept has been extended to photonic, phononic, and mechanical systems. Recently, topological mechanical lattices based on static deformation have been uncovered. However, their topological behaviors are associated with quadratic eigenvalue problems, and they have been explored in an ad hoc manner; a unified Hamiltonian has yet to be developed. In this paper, a topologically effective Hamiltonian is proposed for static topological lattices. Based on this, a general approach for constructing topological lattices with specific topological classifications is developed. The topological, Hermitian, or non-Hermitian characteristics of monomer and dimer lattices are explored for various conditions of spatial periodicity, disorder, and long-range interactions. It is shown that the topological properties of static lattices can be faithfully predicated by the proposed effective Hamiltonian. This work bridges the well-established tight-binding models of condensed-matter physics and static topological lattices, enabling the classification of static topological lattices using the existing framework of topological band theories.

Understanding nanoscale phase separation in Fe(Se, Te) is essential for optimizing its microstructure to enhance superconducting properties, particularly for applications requiring high critical current density ($J_c$) and stability under external perturbations. Electron diffraction and diffuse scattering techniques have traditionally been used to probe compositional fluctuations and phase coexistence along specific crystallographic orientations. Herein, we employ transmission electron microscopy (TEM) to systematically investigate structural phase separation in ${\mathrm{FeSe}}_{0.2}{\mathrm{Te}}_{0.8}$. Our observations reveal that the dominant superconducting phase adopts a tetragonal structure, within which a nanoscale, non-superconducting hexagonal secondary phase, identified as ${\mathrm{Fe}}_7{(\mathrm{Se},\mathrm{Te})}_8$, is embedded. This hexagonal phase exhibits a well-defined orientation relationship with the tetragonal matrix, aligning specific crystallographic planes and directions, which influence phase stability and microstructural evolution. Furthermore, we examine the effects of postannealing and hydrothermal ion deintercalation (HID) treatments on phase separation. The HID treatment effectively reduces the hexagonal phase content, enhancing the homogeneity of the tetragonal matrix. These findings indicate that while phase separation-induced compositional and structural inhomogeneities serve as effective flux pinning centers to enhance $J_c$, excessive phase separation or an increased hexagonal phase fraction may degrade superconducting performance.

We investigate the intrinsic thermal Hall conductivity contributed by optical phonons in a cubic system. The discrete rotational symmetry of the system splits the degeneracy of transverse modes across most regions of wave-vector space, except along a few high-symmetry lines. Consequently, in the presence of an external magnetic field, phonon Berry curvatures become sharply peaked near these high-symmetry lines. We find that the singular distribution of the Berry curvature induces an intrinsic thermal Hall conductivity that is significantly enhanced compared to an isotropic system. It exhibits a nonlinear $BlnB$ dependence on the magnetic field $B$ and a nonmonotonic temperature dependence. At elevated temperatures, it reverses sign and approaches a nonvanishing value asymptotically. Our analysis indicates that the behavior results from competition between contributions from Berry curvatures near different high-symmetry lines.

Achieving altermagnetism (AM) in two-dimensional materials is crucial for advancing the development of novel spintronic devices. This study introduces an innovative strategy to realize AM in monolayer materials by adsorbing nonmagnetic $sp$ impurity atoms to construct planar bridges. Using holey graphyne (HGY) as the research object, first-principles calculations reveal that B and S impurity atoms can modulate the local electronic structure and trigger a superexchange mechanism, inducing a collinear compensated antiferromagnetic ground state with pronounced altermagnetic properties. Among these, the B adsorption system exhibits the best magnetic performance, with a Néel temperature reaching approximately 210 K. This work offers a flexible and effective strategy to achieve AM in single-atomic-layer materials and $p$-electron systems.

$\mathrm{N}{\mathrm{b}}_3\mathrm{B}{\mathrm{r}}_8$, an emergent van der Waals (vdW) magnetic semiconductor, has sparked tremendous interest because of its excellent physicochemical characteristics and potential applications in spintronic and optoelectrical devices. In the present work, the high-temperature and high-pressure magnetic, structural, and electrical transport properties of $\mathrm{N}{\mathrm{b}}_3\mathrm{B}{\mathrm{r}}_8$ were comprehensively investigated using an externally heated diamond-anvil cell (DAC) coupled with in situ Raman spectroscopy and electrical conductivity measurements. $\mathrm{N}{\mathrm{b}}_3\mathrm{B}{\mathrm{r}}_8$ endured a structural transition at 4.4 GPa, followed by the metallization at 25.4 GPa under nonhydrostatic condition. Under hydrostatic condition, the metallization of the sample was delayed by ∼2.0 GPa due to the influence of deviatoric stress. Upon depressurization, the structural transition of $\mathrm{N}{\mathrm{b}}_3\mathrm{B}{\mathrm{r}}_8$ was unveiled to be reversible with the existence of residual strain under different hydrostatic environments. The Ohmic response of $\mathrm{N}{\mathrm{b}}_3\mathrm{B}{\mathrm{r}}_8$ under high pressure was disclosed by the linear correlations between sinusoidal voltage and electrical current (α≈1.0). At a specific pressure of 0.4 GPa, the temperature of magnetic transition in $\mathrm{N}{\mathrm{b}}_3\mathrm{B}{\mathrm{r}}_8$ was determined as 373 K. In conclusion, our obtained high-temperature and high-pressure results on $\mathrm{N}{\mathrm{b}}_3\mathrm{B}{\mathrm{r}}_8$ can lay the foundation for advancing the exploration on the physicochemical properties of other metallic halides $\mathrm{N}{\mathrm{b}}_3{X}_8$ ($X=\mathrm{Cl}$ and I) under extreme conditions, contributing to their prospective developments in spintronic and optoelectronic devices.

We investigate the quantum geometric tensor, which is comprised of the Berry curvature and quantum metric, in a generalized Dirac two-band system with noninteger dispersion $E\left(\mathbf{k}\right)\sim k^{\alpha }$. Our analysis reveals that this type of dispersion introduces significant and novel effects on quantum band geometry. We calculate the Berry curvature and observe its redistribution in momentum space as $\alpha$ varies. Notably, despite this redistribution, the change in Chern number across topological transitions remains quantized as an integer, even for noninteger $\alpha$. We illustrate the physical implications of this redistribution by computing the orbital magnetization. Furthermore, we demonstrate that the Berry curvature and quantum metric peak along the regions of momentum space where the energy band exhibits high curvature. While it is well established that Berry curvature becomes highly concentrated at the band touching points, our findings indicate that they can also accumulate at sharp band corners, away from these band touching points. We further show that while the Berry curvature develops Dirac delta-like peaks away from $\mathbf{k}=0$, the Berry monopole, corresponding to the topological charge, remains located at the origin.

We theoretically show that strongly forbidden oscillations of a specific heat have to exist in metallic phases of some quasi-one-dimensional (Q1D) conductors. They appear due to electron-electron interactions under the condition of the magnetic breakdown phenomenon between the so-called open interference electron orbits. We argue that such forbidden thermodynamic oscillations can exist in Q1D conductors (TMTSF)${}_2{\mathrm{ClO}}_4$ and (Per)${}_2\mathrm{Au}$(mnt)${}_2$, where TMTSF stands for tetramethyltetraselenafulvalene, Per is polycyclic aromatic hydrocarbon, and mnt is mononitrotoluene, and we suggest how to discover them.

We theoretically investigate nonlinear processes driven by a DC spin-electric field in the antiferromagnetic spin-1 Heisenberg model with the system initially in its ground state (the Haldane phase). The DC spin-electric field generates finite spin current and spin accumulation because the field destroys the symmetry-protected topological order. We identify two microscopic mechanisms responsible for the breakdown as well as the crossover between these mechanisms: In weak fields, tripron-antitripron pair creation occurs through the tunneling mechanism, and in strong fields, the system is described by an effective Hamiltonian in which the protecting symmetries are broken. We analyze the numerical results using the Dykhne-Davis-Pechukas theory and the Floquet theory, verifying the universal picture of the many-body Keldysh crossover in DC-driven quantum spin systems.

Two-dimensional (2D) ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ and its derivative materials have recently garnered significant attention due to their rich physical properties, including remarkable ambient stability, high carrier mobility, and exceptional thermal conductivity. In this study, we constructed a class of 2D sextuple-layer materials $ABZ$ ($A/B$ = C, Si, and Ge; $Z$ = N, P, and As) based on the structure of ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ and identified four stable structures through first-principles density functional theory (DFT) calculations. Due to their strong covalent bonds, CSiN and ${\mathrm{C}}_2\mathrm{N}$ monolayers are wide-band-gap semiconductors with band gaps of 3.42 and 5.32 eV, respectively, as determined by the hybrid DFT calculations. Notably, both materials exhibit ultrahigh lattice thermal conductivities, reaching 318 and 694 ${\mathrm{W}\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at room temperatures, respectively. Our analysis attributes the ultrahigh lattice thermal conductivity to their large phonon group velocities and long phonon lifetimes arising from their strong covalent bonds. Additionally, we propose that CSiN and ${\mathrm{C}}_2\mathrm{N}$ could transition from their polar $C_{3\mathrm{v}}$ phase to a metastable centrosymmetric $D_{3\mathrm{d}}$ phase, with transition barriers of 0.89 and 0.70 eV per formula unit, respectively. In contrast, the ${\mathrm{C}}_2\mathrm{P}$ and ${\mathrm{Si}}_2\mathrm{P}$ monolayers exhibit smaller band gaps of 2.77 and 1.39 eV, respectively. This work highlights the potential of ultrahigh thermal conductivity semiconductors and provides valuable insights into designing advanced 2D materials for future applications.

The Euler class characterizes the topology of two real bands isolated from other bands in two dimensions. Despite various intriguing topological properties predicted up to now, the candidate real materials hosting electronic Euler bands are extremely rare. Here, we show that in a quantum spin Hall insulator with two-fold rotation $C_{2z}$ about the $z$ axis, a pair of bands with nontrivial ${\mathbb{Z}}_2$ invariant turn into magnetic Euler bands under in-plane Zeeman field or in-plane ferromagnetic ordering. The resulting magnetic insulator generally carries a nontrivial second Stiefel-Whitney invariant. In particular, when the topmost pair of occupied bands carry a nonzero Euler number, the corresponding magnetic insulator can be called a magnetic Euler insulator. Moreover, the topological phase transition between a trivial magnetic insulator and a magnetic Stiefel-Whitney or Euler insulator is mediated by a stable topological semimetal phase in which Dirac nodes carrying non-Abelian topological charges exhibit braiding processes across the transition. Using the first-principles calculations, we propose various candidate materials hosting magnetic Euler bands. We especially show that ${\mathrm{ZrTe}}_5$ bilayers under in-plane ferromagnetism are a candidate system for magnetic Stiefel-Whitney insulators in which the non-Abelian braiding-induced topological phase transitions can occur under pressure.

In non-Hermitian band structures, exceptional points generically form gapless lines or loops that give rise to extensively many defective eigenstates. In this work, we investigate how they nontrivially contribute to higher-order nonlinear responses by introducing unique singularities in the Berry curvature dipole (BCD) or Berry connection polarizability (BCP). Using a tilted two-dimensional dissipative Dirac model ansatz that harbors an exceptional ring, broken inversion symmetry is shown to give rise to extrinsic (BCD) and intrinsic (BCP) nonlinear Hall behaviors unique to systems with extensive exceptional singularities. In particular, when the non-Hermiticity is increased while keeping the ring radius fixed, the BCD response exhibits a power-law increase, while the BCP response correspondingly decreases. Our work sheds light on how non-Hermiticity can qualitatively control the extent and nature of higher harmonic generation in solids.

Low-energy fermions in semi-Dirac systems depict linear momentum dispersion along one direction while having the features of parabolic dispersion in the other direction. Equilibrium optical responses of such highly anisotropic dispersion are manifested in the direction-dependent optical conductivity tensor. Going beyond the equilibrium framework, we probe the effects of optical-pumping-led nonequilibrium carrier distribution on this system's transmission and polarization rotation. Within the equation of motion approach for a two-band density matrix, we obtain a quasi-steady-state solution for a continuous-wave illumination, in which the population of the two bands is characterized by nonthermal occupancy factors with a strong dependence on amplitude, polarization, and frequency of the pump field. We demonstrate that tuning the pump field parameters significantly modifies the optical conductivity tensor for the probe field, which can have important practical consequences such as selective transmission and tunable hyperbolicity.

We consider an altermagnet subject to the electron attractive potential mediated by bosonic excitations. While altermagnetism suppresses superconductivity, the scattering of electrons on the Fermi surface by thermal bosons suppresses altermagnetism. We show that this leads to the reentrant superconductivity over temperature and to the stabilization of the Fulde-Ferrell-Larkin-Ovchinnikov finite momentum superconducting phase at low temperatures. The effect is mediated by the retardation effects and thus no $d$-wave pairing interaction is required.

Topological semimetals exhibit protected band crossings in momentum space, accompanied by corresponding surface states. Non-Hermitian Hamiltonians introduce geometry-sensitive features that dissolve this bulk-boundary correspondence principle. In this paper, we exemplify this phenomenon by investigating a non-Hermitian 2D stacked SSH chain model with nonreciprocal hopping and on-site gain/loss. We derive an analytical phase diagram in terms of the complex energy gaps in the open-boundary spectrum. The phase diagram reveals the existence of non-Bloch Dirac points, which feature a real spectrum and only appear under open boundary conditions but disappear in Bloch bands under periodic boundary conditions. Due to the reality of the spectrum in the vicinity of non-Bloch Dirac points, we can locally map it to Hermitian semimetals within the Altland-Zirnabuer symmetry classes. Based on this mapping, we demonstrate that non-Bloch Dirac points are characterized by an integer topological charge. Unlike the band crossings in Hermitian semimetals, the locations of the non-Bloch Dirac points under different boundary geometries do not match each other, indicating a geometry-dependent bulk-boundary correspondence in non-Hermitian semimetals. Our findings provide new pathways into establishing unconventional bulk-boundary correspondence for non-Bloch Dirac metals in non-Hermitian systems.

Direct-band-gap light sources from group IV materials are highly desired for photonic integration. Among the possible candidates is the hex-${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ system, which has been demonstrated to have a direct band gap at least for $x>65\%$. Recently, Ge-rich heterostructures of hex-${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x/{\mathrm{Si}}_{1-y}{\mathrm{Ge}}_y$ ($x<y$) have been demonstrated to have a type-I alignment. This unlocks opportunities for devices utilizing low-dimensional structures, such as quantum wells (QWs), based on group IV materials. Multi-quantum-well (MQW) structures can significantly reduce lasing thresholds, and a full understanding of the growth kinetics is necessary to grow MQWs with identical well thicknesses. Here, we report a study of hex-${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ multishells, of which the growth rate increases by a factor 4 over a shell thickness of 500 nm, indicating nucleation-limited growth. We present a model that hints that the increasing growth rate is due to the accumulation of cubic stacking faults at the growth front. This proposed mechanism is generic for the hex-SiGe system, and it has to be considered for any multilayer structure of hex-SiGe.

Drude weight, historically associated with the longitudinal Drude conductivity, can be generalized to describe the transverse or Hall component of the extrinsic conductivity tensor. In particular, transverse Drude weights, such as band geometric quantities Berry curvature dipole and spin vorticity, manifest themselves through the extrinsic second-order nonlinear Hall effect and extrinsic linear spin Hall effect (SHE) in diffusive transport, respectively. In this work, we uncover a new class of intrinsic Hall effects in quantum transport regime, termed the quantum intrinsic Hall effect (QIHE), which is the manifestation of system symmetry through intrinsic transport phenomena. For a given Hamiltonian, its transport characteristics can be revealed either intrinsically through QIHE in quantum ballistic transport or extrinsically via the transverse Drude weight in diffusive transport, where both intrinsic and extrinsic effects share the same salient transport features governed by symmetry of the Hamiltonian. The physical origin of QIHE is attributed to quantum boundary scattering of the measurement setup that respects the system symmetry, as exemplified by the contact resistance of a two-terminal ballistic conductor. We demonstrate our findings by studying the $T$-even ($T$, time-reversal) nonlinear charge Hall effect induced by Berry curvature dipole and the $T$-odd spin Hall effect in altermagnets, thereby revealing the quantum intrinsic nature of these effects. Our work explicitly resolves the intrinsic-extrinsic classification paradox when describing quantum transport properties using the language of bulk transport theory, and paves a way towards quantum transport manifestation of band geometric characteristics.