Information-theoretic quantities such as Renyi entropies show a remarkable universality in their late-time behavior across a variety of chaotic many-body systems. Understanding how such common features emerge from very different microscopic dynamics remains an important challenge. In this work, we address this question in a class of Brownian models with random time-dependent Hamiltonians and a variety of different microscopic couplings. In any such model, the Lorentzian time evolution of the $n\mathrm{th}$ Renyi entropy can be mapped to evolution by a Euclidean Hamiltonian on $2n$ copies of the system. We provide evidence that in systems with no symmetries, the low-energy excitations of the Euclidean Hamiltonian are universally given by a gapped quasiparticlelike band. The eigenstates in this band are plane waves of locally dressed domain walls between ferromagnetic ground states associated with two permutations in the symmetric group ${\mathcal{S}}_n$. These excitations give rise to the membrane picture of entanglement growth, with the membrane tension determined by their dispersion relation. We establish this structure in a variety of cases using analytical perturbative methods and numerical variational techniques and extract the associated dispersion relations and membrane tensions for the second and third Renyi entropies. For the third Renyi entropy, we argue that phase transitions in the membrane tension as a function of velocity are needed to ensure that physical constraints on the membrane tension are satisfied. Overall, this structure provides an understanding of entanglement dynamics in terms of a universal set of gapped low-lying modes, which may also apply to systems with time-independent Hamiltonians.

In this work, we introduce a method that enables precise control of the orbital angular momentum (OAM) of Bessel vortex beams by harnessing the dynamics of optical patterns generated within a photorefractive (PR) feedback system. By systematically adjusting key parameters—such as the coupling strength between the beams, the tilt angle of the feedback mirror, and the topological charge (both integer and fractional) of the incident beams—we demonstrate how the evolution and motion of the resulting optical patterns can be exploited to modulate and control the OAM. Through our fluid-dynamic analogical framework, we reveal the rotational dynamics of the patterns as a tangible manifestation of the intrinsic vortex nature of high-order Bessel beams. We further conducted a detailed investigation into the evolution of OAM, including fractional OAM states, and demonstrated that the dynamic behavior of the patterns not only reflects but also enhances the OAM. These insights pave the way for new possibilities in advanced optical manipulation and communication systems.

Understanding the magnetic properties of rare-earth iron garnet ultrathin films subjected to a strain is of essence from both fundamental science and technological perspectives. In this work, we report on the results of a combined first-principles calculations and classical Monte Carlo simulations study of magnetic properties of gadolinium iron garnet thin-films subjected to a uniaxial strain. We employ first-principles calculations to compute the magnetic exchange coupling constants for thin films subjected to uniaxial strains including both compressive and tensile cases. The magnetic exchange coupling constants were then used to construct an effective magnetic Hamiltonian, which includes symmetry-breaking effects, and perform Monte Carlo simulations. Using the latter, we study the dependences of magnetic properties on temperature and strain in gadolinium iron garnet thin-film systems, subjected to a uniaxial strain. To further advance our understanding of the magnetic behavior, we also consider a simple analytical model, which is based on the Néel molecular field theory for ferrimagnetics and incorporates magnetic exchange coupling constants taken from the first-principles calculations. The case of uniaxial strains, considered in this work, is compared to the behavior of biaxially-strained thin films, studied in a previous work, and the theoretical results of this work are also compared with available experimental data on rare-earth iron garnets subjected to an external strain. The implications of the obtained results for use of layered rare-earth iron garnets-based materials for magnetic technologies are also discussed.

Lee-Yang theory is central to the analysis of thermal phase transitions. However, the underlying mechanism of the theory and the nature of Lee-Yang zeros in quantum many-body systems remain elusive. Here, we develop a unified framework for understanding quantum phase transitions from fidelity zeros induced by symmetry breaking. These zeros, arising from transitions between symmetry sectors, obey the Lee-Yang theorem and give rise to fidelity edges near critical points. Quantum criticality is further characterized through the finite-size scaling of fidelity zeros. As concrete examples, we investigate fidelity zeros analytically in one-dimensional and numerically in two-dimensional quantum Ising models under a complex magnetic field, showing excellent agreement with analytical theory and with quantum Monte Carlo and tensor-network simulations. Our results provide insights into the mechanism of Lee-Yang theory and open avenues for exploring unexplored landscapes of phase transitions in quantum many-body systems.

Elastic neutron scattering measurements have been carried out on a single crystal of ${\mathrm{La}}_{1.6-x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ at optimal doping for superconductivity, $x$ = 0.19, in magnetic fields up to 8 T, applied $\parallel c$. At zero magnetic field, these measurements of the intensity of parallel spin stripe quasi-Bragg peaks show a departure from a weak sloping background below $T_N$ = 40 K, with a $\sim$ linear growth in intensity that is bounded between superconducting $T_c^{\text{(onset)}}$ = 26 K and $T_c^{\text{(mid)}}$ = 13 K. Below $T_c^{\text{(mid)}}$, the order parameter plateaus and subsequently displays a strong increase below $T_{\text{Nd}}\sim$ 8 K. This strong, low-temperature increase is due to weak coupling between the magnetism in the ${\mathrm{CuO}}_2$ planes and that of ${\mathrm{Nd}}^{3+}$ moments between the planes. A magnetic field $\parallel c>$ 1.5 T suppresses this low-temperature rise of the order parameter, as the ${\mathrm{Nd}}^{3+}$ moments polarize in the field, and the coupled ${\mathrm{Nd}}^{3+}\text{−}{\mathrm{CuO}}_2$ magnetism can no longer participate in the incommensurate, parallel spin stripe structure. At $T=10\mathrm{K}$, above $T_{\text{Nd}}$ but below $T_c^{\text{(mid)}}$, the stripe intensity weakly decreases with field, consistent with vortex-induced disorder of short-range stripes in $d$-wave superconducting regions. For $T\ge 17\mathrm{K}$, no measurable field dependence is observed, showing that a uniform $H\parallel c<8$ T does not perturb ${\mathrm{CuO}}_2$ stripe magnetism. A plateau at $T_c^{\text{(mid)}}$ persists across all fields. These results are discussed in the context of earlier studies of the magnetic field dependence on parallel spin stripes in ${\mathrm{La}}_{1.6-x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_x{\mathrm{CuO}}_4, {\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$, and ${\mathrm{La}}_{2-x}{\mathrm{Ba}}_x{\mathrm{CuO}}_4$.

Heterostructures of normal metals (N) and magnetic insulators (F) show paradigmatic effects, such as spin-Hall magnetoresistance and electric drag currents. These effects are linear in the applied electric field $E\left(\omega \right)$. Normal metal–magnetic insulator heterostructures also exhibit a characteristic nonlinear response quadratic in $E\left(\omega \right)$, referred to as unidirectional spin-Hall magnetoresistance or spin-torque diode effect. In this article, we develop a theory of the bilinear response of FN bilayers and NFN trilayers for finite frequencies $\omega$ of the driving field and for four contributions that have been previously considered in the literature: Joule heating, phononmediated unidirectional magnetoresistance, the spin-torque diode effect, and magnonic unidirectional spin-Hall magnetoresistance. We identify their distinct dependencies on frequency and the magnetization direction of the magnetic insulator and examine their scaling with magnetic field and system geometry, providing a framework for experimental differentiation.

Conventional theory holds that high quality factor (Q) surface acoustic wave modes cannot exist within the radiation continuum due to inevitable coupling with bulk modes. Here we demonstrate that Brillouin zone folding enables the emergence of two types of high-Q resonances—bound states in the continuum and guided mode resonances—within the sound cone. Using rigorous theoretical analysis, we reveal that these resonances can be robustly sustained and their Q tuned across a broad spectral range via controlled structural perturbations. We numerically validate our predictions on two distinct platforms: topological Rayleigh-type edge modes supported by periodic resonator arrays on a piezoelectric half-space, and topological Love-type interface modes in groove-type phononic crystals on heterogeneous substrates. These surface-confined modes exhibit controllable radiative coupling, providing a versatile mechanism for engineering acoustic-matter interactions. Our results establish a unified framework for accessing high-Q surface acoustic waves in the continuum, with implications for chip-scale acoustic devices in sensing, microfluidics, and non-Hermitian acoustics.

I introduce a mode-resolved quantum Langevin method that tracks coherent phonon heat transport at any temperature from a single eigendecomposition of the dynamical matrix. The result is a closed-form, multiterminal conductance $G_{\alpha \beta }\left(T\right)$. I derive the expressions and provide an analytical connection to nonequilibrium Green's functions (NEGF), recovering the Landauer–Büttiker limit under weak, diagonal damping. Benchmarks on a harmonic chain reproduce the canonical $\kappa \propto T$ law. A vacancy-defected carbon nanotube shows quantitative agreement with NEGF transmission spectra. I then apply the method to proteins viewed as multiterminal elastic networks, where surface patches and solvent interfaces serve as contacts. The framework yields the full $G_{\alpha \beta }\left(T\right)$ and a mode-level diagnostic linking conductance, frequency, and localization. The ensuing spectral weights reveal a mobility edge via a temperature crossover $T_c\simeq \hslash {\omega }_c/k_B$. The approach yields fast, interpretable predictions for complex phonon systems from a single eigensolve.

Kramers-Wannier duality, a hallmark of the Ising model, has recently gained renewed interest through its reinterpretation as a noninvertible symmetry with a state-level action. Using sequential quantum circuits (SQC), we argue that this duality governs the stability of quantum many-body scar (QMBS) states in a nonintegrable model, depending on whether the dual preserves the embedding conditions for scarring. This is supported by good agreement between first-order perturbation theory and numerics, which capture scar dynamics despite chaotic spectra. Our results establish noninvertible dualities as both a generative mechanism and a diagnostic tool for quantum many-body scarring, offering a generalized symmetry-based route to weak ergodicity breaking.

Magnetic interactions in an antiferromagnet govern the spin moment carried by magnons and the strength of multimagnon interactions that lead to magnetization relaxation. We present a numerical method to generate a four-magnon interactions Hamiltonian by fourth-rank tensor and apply it to an antiferromagnetic insulator NiO, where magnetic dipolar interactions (MDIs) have non-negligible effects on the magnon states, for investigating four-magnon interactions-induced magnon decay rates, by taking into account intra- and intermode interactions. First, we confirmed the suppressed magnon spin moment of two magnon modes, labeled as $\alpha$ and $\beta$ modes, owing to non-spin-conserving interactions of the MDIs. An applied magnetizing field $B^z$ enhanced the magnon spin moment of each magnon mode by increasing the spin moment contribution from one Ni sublattice, while decreasing it from another sublattice. Second, by expressing the four-magnon scattering probability in the fourth-rank tensor form, we found that the low magnon decay rates of both magnon modes are mainly caused by the suppressed magnon spin moment. The applied magnetizing field promotes the intermode and suppresses the intramode interactions contribution to the magnon decay rates.

The Holstein-Primakoff boson representation of quantum spins and associated large-$S$ expansion have been the standard framework for describing the spin wave excitations in magnetically order phases of quantum spin systems. However, we will show that the omission of projection operators and normal ordering in this representation can produce incorrect magnon Hamiltonians for finite $S$. We will present the exact normal-ordered forms of the finite-$S$ projection operators and projected Holstein-Primakoff boson representations of spin and quadrupole operators, which can produce exact two-magnon interaction terms under ferromagnetic or fully polarized states. We will also discuss the difficulties of applying this projected representation to antiferromagnetic spin wave theory.

The temperature dependence of most solid-state properties is dominated by lattice vibrations, but metals display notable purely electronic effects at low temperature, such as the linear specific heat and the linear entropy, that were derived by Sommerfeld for the noninteracting electron gas via the low-temperature expansion of Fermi–Dirac integrals. Here we treat temperature as a perturbation within density-functional perturbation theory (DFPT). For finite temperature, we show how self-consistency screens the bare, temperature-induced density change obtained in the noninteracting picture: the inverse transpose of the electronic dielectric operator, that includes Adler-Wiser and a term related to the shift in Fermi level, links the self-consistent density response to the bare thermal density change. This approach is implemented in DFTK, and demonstrated by the computation of the second-order derivative of the free energy, and the first-order derivative of entropy for aluminum. Then, we examine the $T\to 0$ limit. The finite temperature formalism contains divergences, that we cure using the Sommerfeld expansion to analyze metallic systems at 0 K. The electronic free energy is quadratic in $T$ provided the Fermi level is not at a Van Hove singularity of the density of states. If the latter happens, another temperature behavior might appear, depending on the type of Van Hove singularity, that we analyze. Our formulation applies to systems periodic in one, two, or three dimensions, and provides a basis for studying temperature-dependent electronic instabilities (e.g., charge-density waves) within density-functional theory and DFPT.

The combination of ferromagnetic metals and nonmagnetic light metals, exemplified by the ${\text{Co}}_{80\text{−}x}{\text{Fe}}_x{\text{B}}_{20}\text{/Ti}$ bilayer heterostructures, has emerged as an outstanding platform for achieving terahertz (THz) emission based on both spin-to-charge and orbital-to-charge current conversion. Although some of many-body phenomena based on the interactions among charge, spin, orbital, and lattice degrees of freedom in such heterostructures have been investigated by using THz emission spectroscopy recently, other many-body effects affecting the THz absorption properties of these bilayer systems still remain relatively unexplored. Here we characterize the THz transmission/absorption properties of ${\text{Co}}_{40}{\text{Fe}}_{40}{\text{B}}_{20}$ (CFB)/Ti heterostructures and investigate the many-body interactions associated with photons, charge carriers, and phonons in them. It is demonstrated that the heterostructures exhibit metallic-type charge carrier behavior in the range of 0.1–1.2 THz, whereas a significant Fano asymmetric line shape is observed in the regime of 1.2–2 THz. The Fano resonance can be attributed to the strong coupling between free electrons and interface phonons. More importantly, we show that this coupling can be modulated by pumping/exciting the heterostructures with a continuous-wave laser. Specifically, the CFB(15 nm)/Ti sample exhibits a large modulation depth of approximately 82.5% at 1.65 THz under a power density of $191{\mathrm{mW}/\mathrm{cm}}^2$. Furthermore, by fitting the experimental data with the Drude-Fano model, we also obtain the characteristic parameters of the charge carriers and electron-phonon coupling, as well as their dependencies upon the pump power density and CFB thickness. These findings not only offer a deeper understanding of the many-body THz response in CFB/Ti systems and their active control but also advance the research on CFB-based THz devices.

Exploiting the valley degree of freedom introduces a paradigm for advancing quantum information technology. Currently, the investigation on spontaneous valley polarization mainly focuses on two major types of systems. One type of magnetic systems is by breaking the time-reversal symmetry, the other is ferroelectric materials through breaking the inversion symmetry. Might there be additional scenarios? Here, we propose to realize spontaneous valley polarization by breaking the mirror symmetry in the altermagnets, named type III valley polarization. Through symmetry analysis and first-principles calculations, we confirm that this mechanism is feasible in non-Janus ${\mathrm{Fe}}_2{\mathrm{WS}}_2{\mathrm{Se}}_2$. Monolayer non-Janus and Janus ${\mathrm{Fe}}_2{\mathrm{WS}}_2{\mathrm{Se}}_2$ are stable Néel-type antiferromagnetic state with the direct band gap semiconductor. More interestingly, their magnetic anisotropy energy exhibits the rare biaxial anisotropy and a four-leaf clover shape in the xy plane, while the xz and yz planes show the common uniaxial anisotropy. This originated from the fourth-order single ion interactions. More importantly, the valley splitting is spontaneously generated in the non-Janus ${\mathrm{Fe}}_2{\mathrm{WS}}_2{\mathrm{Se}}_2$ due to the ${\mathrm{M}}_{xy}$ symmetry breaking, without requiring the SOC effect. Both the non-Janus and Janus ${\mathrm{Fe}}_2{\mathrm{WS}}_2{\mathrm{Se}}_2$ exhibit diverse valley polarization and anomalous valley Hall effect properties. In addition, the magnitude and direction of valley polarization can be effectively tuned by the biaxial strain and magnetic field. Our findings not only expand the realization system of spontaneous valley polarization, but also provide a theoretical basis for the high-density storage of valley degrees of freedom.

In translationally invariant semiconductors that host exciton bound states, one can define an infinite number of possible exciton Berry connections. These correspond to the different ways in which a many-body exciton state, at fixed total momentum, can be decomposed into free electron and hole Bloch states that are entangled by an exciton envelope wave function. Inspired by the modern theory of polarization, we define an exciton projected position operator whose eigenvalues single out two unique choices of exciton Berry phase and associated Berry connection—one for electrons, and one for holes. We clarify the physical meaning of these exciton Berry phases and provide a discrete Wilson loop formulation that allows for their numerical calculation without a smooth gauge. As a corollary, we obtain a gauge-invariant expression for the exciton polarization at a given total momentum, i.e., the mean separation of the electron and hole within the exciton wave function. In the presence of crystalline inversion symmetry, the electron and hole exciton Berry phases are quantized to the same value and we derive how this value can be expressed in terms of inversion eigenvalues of the many-body exciton state. We then consider $C_2\mathcal{T}$ symmetry, for which no symmetry eigenvalues are available as it is antiunitary, and confirm that the exciton Berry phase remains quantized and still diagnoses topologically distinct exciton bands. The notion of shift excitons, whose exciton Wannier states are displaced from those of the noninteracting bands by a quantized amount, can therefore be generalized beyond symmetry indicators.

We give a bosonic realization of the SU(3) antiferromagnetic Heisenberg (AFH) chain in the alternating conjugate representation, and study its phase diagram as a function of staggered interactions and anisotropy along the $T^3$ and $T^8$ directions. Unlike the SU(2) case, we observe a chiral-reversed quantum phase transition, where each competing phase is adiabatically connected to one of the chiral Haldane phases predicted in the SU(3) AFH chain with local adjoint representation. In the vicinity of the Heisenberg point, we identify a symmetry-protected topological state that appears at the first excited energy level. We also study the spontaneous ${\mathbb{Z}}_3$ symmetry breaking of the system, and provide a variational wave function that captures the transition from the topological phase to the trivial phase. Finally, we propose an experimental realization of our bosonic model by two spin-1/2 bosons in an optical lattice.

The concept of topological insulators has attracted significant interests due to the presence of topologically protected states following the bulk-boundary correspondence. Higher-order topology has extended this principle and hosts lower-dimensional topological corner states. Recent studies have shown that the hybridization of a gapless bulk state and nontrivial topology could lead to a large-area topological state in classical systems. In this Letter, we design an acoustic heterostructure that hybridizes a second-order topological insulator layer with a Dirac material layer, based on the Benalcazar-Bernevig-Hughes model. This hybrid system generates a topological hybrid corner state pinned at zero energy within a complete band gap. Crucially, this topological hybrid corner state exhibits tunable large-area localization controlled by the number of outer layers and the coupling strength of the inner region. Furthermore, we experimentally demonstrate this state through pressure field distributions and intensity spectra, showing excellent agreement with simulations and theoretical analyses. The stable eigenfrequency and scalable confinement area of the large-area corner state provide the possibility to advance functional acoustic devices, such as energy harvesters or broadband sensors, where adaptable wave control is essential.

The nonlinear Hall effect has recently garnered significant attention as a powerful probe of Fermi surface quantum geometry in metals. While current studies mainly focus on the nonlinear Hall response driven by quasistatic electric fields of low frequencies, the extension of the response to higher frequencies is another promising frontier, which introduces quantum geometry into interband transitions. Here, we demonstrate that a specific nonlinear Hall response, namely, the second harmonic Hall (SHH) response, can arise from interband transitions. We establish the quantum geometric origin of the SHH response and show that interband quantum geometry dominates the SHH response when driven near interband resonance. Crucially, we find that the interband SHH response in insulators exhibits strong frequency dispersion, manifesting the breakdown of Kleinman's conjecture in nonlinear optics. This connects the SHH response to the breakdown of Kleinman's conjecture and reveals that frequency-dispersive insulators generally allow the SHH response. Furthermore, we predict a giant SHH susceptibility in gated strained bilayer graphene and propose that one can apply the polarization resolved second harmonic microscopy to detect the SHH response there.

The interplay of quantum geometry and interactions determines the correlated state properties of flat bands. Here, we investigate the ideal quantum geometry (IQG), i.e., the property that the trace of quantum metric equals the Berry curvature, in the surface flat bands of rhombohedrally stacked graphene (RG) multilayers. We show that RG represents a class of semimetals with IQG, among which only RG has a nonvanishing IQG at the center of the surface bands. In the presence of long-range hoppings, a displacement field polarizes the electron density to one of the two surfaces, stabilizing the IQG and boosting transitions to correlated phases like superconductivity. Analyzing the superfluid stiffness of the superconducting state in a many-layer RG, we reveal a heavy-fermion picture where the “heavy electrons” carry a nonzero supercurrent. This unusual behavior arises from the IQG of the surface states, which suggests a large fraction of supercurrent running on the surface of RG.