Hafnium dioxide ($\mathrm{Hf}{\mathrm{O}}_2$), commonly known as hafnia, serves as a critical high-$k$ gate dielectric material in complementary metal-oxide-semiconductor (CMOS) devices and is also widely utilized in dynamic random-access memory (DRAM) capacitors. To gain better understanding of their physical properties, crystalline structures and dielectric constants of the three orthorhombic phases (OI-Pbca, OII-Pnma, OIII-$Pca{2}_1$) of $\mathrm{Hf}{\mathrm{O}}_2$ under mechanical strain have been investigated by first-principles calculations. Strain modifies both the mode effective charges and the frequencies of infrared-active (IR-active) phonon modes. The dielectric constant is directly proportional to the former and inversely proportional to the latter. Moreover, lattice-dynamics simulations revealed that large biaxial/triaxial tensile strains induce a phase transition from the ferroelectric phase (OIII-$Pca{2}_1$) to antipolar phase (OVIII-Pbcn), which arises from the coordination number change in half of the oxygen atoms. These results demonstrate strain engineering as a powerful means to control and modulate the dielectric properties and phase stabilities of $\mathrm{Hf}{\mathrm{O}}_2$.

An excess of low-frequency vibrational states beyond the Debye prediction—known as the boson peak—is a universal feature of disordered materials, yet its microscopic origin and connection to atomic-scale structural disorder remain unresolved. Here we study the microscopic origin and real time evolution of the boson peak during crystallization of amorphous Ge-Sb-Te by carrying out large-scale molecular dynamics simulations using machine learning interatomic potentials. The boson peak frequency is found to match with the transverse Ioffe-Regel crossover frequency throughout crystallization. As crystallization proceeds, the boson peak shifts to higher frequencies and its intensity progressively weakens, while the macroscopic shear modulus increases concurrently. The square-root scaling of the boson peak frequency with the shear modulus is more pronounced in mechanically soft and interfacial regions than in stiff regions. Atom-resolved vibrational anomaly highlights the population of quasilocalized low-frequency modes in the mechanically soft regions. The anticorrelation between the shear modulus and the boson peak intensity persists even at atomic scales in both amorphous and partially crystalline phases. Our large-scale atomistic simulations of structural ordering provide a microscopic perspective on the interplay between structural ordering, local elastic rigidity, and vibrational anomalies in real materials.

We investigate a novel class of topological superconducting phases protected by exact fermion-parity symmetry and average crystalline symmetries. These phases belong to the broader class of average crystalline symmetry-protected topological (ACSPT) states and include numerous examples of intrinsic ACSPTs—topological phases that arise only in the presence of disorder or decoherence. Unlike conventional symmetry-protected topological (SPT) phases, which require exact symmetry protection, average SPT (ASPT) phases remain robust as long as the symmetry is restored on average across disorder realizations or mixed-state ensembles. To classify these phases, we extend the real-space block state construction framework to account for average crystalline symmetries. In this generalized setting, lower-dimensional cells are decorated with ASPT phases, and the obstruction-free conditions are reformulated to incorporate the constraints imposed by average symmetry at block intersections. This provides a physically transparent and systematic method for classifying ASPTs with spatial symmetries that are only preserved statistically. We further validate our classification using a generalized spectral sequence analysis, which serves as an independent consistency check. Our results demonstrate that many crystalline topological superconductors remain well defined under realistic imperfections, and they uncover a rich landscape of intrinsically average-symmetry-protected phases that have no analog in clean systems.

We investigate the dissipative spectral form factor (DSFF)—a widely used probe of non-Hermitian quantum chaos—in the elliptic Ginibre unitary ensemble (eGinUE), which interpolates between the non-Hermitian Ginibre unitary ensemble (GinUE) and the Hermitian Gaussian unitary ensemble (GUE) via a symmetry breaking parameter. We derive exact finite-dimensional results and large-dimensional approximations for the DSFF, revealing a scaling relationship that connects the DSFF of eGinUE to that of GinUE and the spectral form factor of GUE. This relation explains the distinct timescales underlying the characteristic dip-ramp-plateau structure across GinUE, GUE, and crossover regimes. Additionally, we refine estimates of dip-ramp and ramp-plateau transition times for different symmetry regimes. We validate our results with Monte Carlo simulations and demonstrate applications to paradigmatic quantum-chaotic systems: the crossover Sachdev-Ye-Kitaev model and the crossover power-law banded random matrices. We highlight an analogy between eGinUE eigenvalues and the positions of a rotating fermionic gas in a two-dimensional anisotropic trap.

Short midinfrared laser pulses efficiently facilitate ultrafast manipulation of ferroic order parameters, including the full reversal of magnetization or ferroelectric polarization, with the invoked mechanisms relating to the properties of polar phonons in ionic crystals. Much less is known, however, about the behavior of such order parameters in response to an excitation in the far-infrared range, where phonons have larger oscillator strengths and are more damped. Here we investigate transient crystallographic strains and polarization switching in ferroelectric barium titanate ($\mathrm{BaTi}{\mathrm{O}}_3$) driven by an excitation in the frequency range of 5–8 THz, or wavelengths of 35–60 µm. We find that switching persists in a large part of this range, but is governed primarily by optical absorption rather than by the longitudinal optical phonons or epsilon-near-zero conditions that dominate in the mid-infrared regime.

The spin nematic phase, characterized by long-range order of spin quadrupole moments in the absence of dipolar magnetism, presents a significant challenge for conventional experimental detection. We propose a method to detect this elusive order in quantum magnets with an illustration in the spin-1 triangular lattice Mott insulator. By integrating out the phonon degrees of freedom, we obtain a phase diagram with substantially enlarged regions for the spin-nematic and spin-nematic-supersolid phases. We then demonstrate that through the spin-lattice coupling, the emergence of spin nematic order imprints a distinctive signature onto the phonon spectra, providing a clear spectroscopic signature for the quadrupolar order. Our formalism offers a direct and powerful method to uncover the hidden spin nematicity, opening a pathway for diagnosing multipolar orders in quantum magnets.

We obtain the $\mathrm{p}4\mathrm{m}$-symmetric group convolutional neural network (GCNN) representations of the lowest energy eigenstate of the quantum dimer model on an $L\times L$ square-lattice in each of the $(L^2+18L+72)/8$ irreducible representations (irreps) of the lattice space group and use these to investigate the competition between columnar, plaquette and mixed phases. The networks are optimized within each irrep by minimizing the energy, which is estimated from samples obtained via an efficient directed loop sampler. In extensive benchmarks, we show excellent agreement in energy estimates, order parameters and correlation functions with exact diagonalization or quantum Monte Carlo for systems of sizes $8\le L\le 32$. Analysis of the scaling of the gaps in different representation sectors for systems of sizes up to $L=32$ suggest a fourfold-degenerate ground state for $V\le 0.4$ narrowing the regime of possible mixed/plaquette phases to $0.4<V<1$. Our results show that GCNN is a powerful tool for investigating ground-state phase diagrams. The approach paves the way for even more accurate results by producing highly accurate variational baseline wave functions for quantum Monte Carlo approaches.

The regulation of magnetic anisotropy in two-dimensional (2D) van der Waals (vdW) ferromagnets is critical for enabling spintronic and solid-state cooling applications, yet the microscopic doping mechanism remains poorly understood, as conventional ideal-lattice models fail to reconcile the moderate structural and magnetic evolution observed in experiments. In this work, we investigate Ni-doped ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$, a room-temperature 2D ferromagnet, combining systematic magnetization measurements and first-principles calculations based on the realistic defective lattice structure of ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2$. We demonstrate an intrinsic defect-assisted occupation mechanism: Ni dopants preferentially substitute the preexisting interstitial Fe atoms in the vdW gap rather than inserting into empty interlayer sites. This mechanism accounts well for all our experimental observations, including the minor $c$-axis contraction, the 80% reduction of magnetocrystalline anisotropy energy with preserved out-of-plane easy axis, and the monotonic decrease of Curie temperature ($T_{\text{C}}$) and saturation magnetization. Furthermore, we demonstrate that Ni doping effectively tunes the anisotropic magnetocaloric effect: The anisotropy of magnetic entropy change decreases from 0.68 to $0.29\text{J}{\text{kg}}^{-1}{\text{K}}^{-1}$, while the relative cooling power exhibits a nonmonotonic evolution, reaching an optimal value of $156\text{J}{\text{kg}}^{-1}$ at 4.6% Ni doping. The evolution of critical exponents $n$ and $m$ confirms that Ni doping introduces magnetic disorder, broadening the magnetic phase transition. Our results resolve the discrepancy between ideal-lattice theoretical predictions and experimental observations, providing a clear microscopic picture for anisotropy engineering in 2D magnets.

We study the surface density of states in $p$-wave unconventional magnet/spin-singlet $s$-wave superconductor hybrid systems ($p$-wave unconventional magnetic superconductors). Owing to the noncollinear spin structure in $p$-wave unconventional magnets, the spin-singlet $s$-wave pair potential behaves as the spin-triplet $p$-wave superconductivity. As a result, zero-energy flat bands can emerge at the edge. Analyzing the pair amplitude at the edge, odd-frequency spin-triplet even-parity pairing is induced in the presence of zero-energy flat bands, while even-frequency spin-singlet even parity remains. We also demonstrate the Josephson current in superconducting junctions with $p$-wave unconventional magnet/spin-singlet $s$-wave superconductor hybrid systems. By the cooperation of the spin-singlet $s$-wave pair potential and the $p$-wave unconventional magnetic order, the coupling of the spin-singlet even-parity pairings in junctions generates the first harmonics of the Josephson current. In addition, the temperature dependence of the maximum Josephson current can be tuned by the chemical potential, which determines the generation of zero-energy flat bands. Our results indicate that the $s+p$-wave-like superconducting state is generated in $p$-wave unconventional magnet/$s$-wave superconductor hybrid systems.

Acoustic helical dichroism (HD) arises from the interaction between vortex beams carrying orbital angular momentum (OAM) and chiral media, yet such chiral sound-matter interactions are typically weak. Here, we employ quasibound states in the continuum (QBICs) in acoustic metacavities composed of coupled Helmholtz resonators to enhance acoustic HD. We design both achiral and chiral metacavities that support QBICs in the form of vortex states with high $Q$ factors. Using full-wave numerical simulations, we show that the QBICs in the achiral metacavities cannot enhance acoustic HD due to the absence of a chiral wave front. In contrast, the chiral metacavity exhibits a pronounced HD enhancement through the QBICs with a three-dimensional (3D) helical wave front, which can be excited by incident waves either with or without OAM. Our work identifies two essential requirements for enhancing acoustic HD effect via QBICs: a high $Q$ factor of the states and 3D chirality of the state fields, which usually compromise each other in conventional acoustic resonators. The findings open avenues for achieving strong chiral sound-matter interactions, with potential applications in acoustic chiral sensing and acoustic OAM manipulation.

We study the topological properties of rhombohedrally stacked $N$-layer Su-Schrieffer-Heeger networks with interlayer coupling. We find that these systems exhibit $2N$-fold degenerate zero-energy edge states with winding number $W=N$, providing a direct route to high winding number topological phases where $W$ equals the layer number. Using effective Hamiltonian theory, we demonstrate that the winding number scales linearly with $N$ through a layer-by-layer topological amplification mechanism. We introduce the Wigner entropy as a detection method for these edge states, showing that topological edge states exhibit significantly enhanced Wigner entropy compared to bulk states. Our results establish rhombohedral stacking as a systematic approach for engineering high winding number topological insulators with potential applications in quantum information processing.

We introduce FIRE-Swap, a first-principles-based framework for sampling representative compositional structures in complex perovskites using machine-learning interatomic potentials. By combining Monte Carlo chemical swaps with geometric relaxation, the method treats chemical and geometric degrees of freedom concurrently. Applied to lead magnesium niobate (PMN), lead zirconate titanate (PZT), and lead strontium titanate (PST), FIRE-Swap robustly predicts rock-salt-like chemical order in PMN, but not in the isovalent solid solutions PZT and PST with the same mixing ratio. For PMN, it further reveals anchored Nb clusters that host interconnected, noncoarsened polar nanoregions. These results provide a mesoscale structural basis for understanding relaxor ferroelectricity and establish FIRE-Swap as a practical route toward systematic, first-principles modeling of complex perovskites and related substitutionally disordered materials.

A result by Gioia and Wang [Phys. Rev. X 12, 031007 (2022)] showed that translationally symmetric states having nonzero momentum are necessarily long-range entangled (LRE). Here, we consider the following question: Can a notion of momentum for nontranslation-symmetric states directly encode the nature of their entanglement, as it does for translation-symmetric states? We show the answer is affirmative for one-dimensional (1D) systems, while higher-dimensional extensions and topologically ordered systems require further work. While the Gioia and Wang result applies to states connected via finite-depth quantum circuits to a translation-symmetric state, it is often impractical to find such a circuit to determine the nature of the entanglement of states that break translation symmetry. Here, instead of translation eigenstates, we focus on the many-body momentum distribution and the expectation value of the translation operator in many-body states of systems having broken translation symmetry. We show that in the continuum limit the magnitude of the expectation value of the translation operator $|\langle T\rangle |$ necessarily goes to 1 for delocalized states, a proxy for LRE states in 1D systems. This result can be seen as a momentum-space version of Resta's formula for the localization length. We investigate how accurate our results are in different lattice models with and without well-defined continuum limits. To that end, we introduce two models: a deterministic version of the random dimer model, illustrating the role of the thermodynamic and continuum limits for our result at a lattice level, and a simplified version of the Aubry-Andre model, with commensurate hopping for both momentum and position space. Finally, we use the random dimer model as a test case for the accuracy of $|\langle T\rangle |$ as a localization (and thus entanglement) probe for 1D periodic lattice models without a well-defined continuum limit.

Extreme ultraviolet transient gratings (EUV TG) are a recently developed tool, originally conceived for probing thermoelastic dynamics and more recently extended to magnetic dynamics through the use of core-resonant EUV probing. Resonant EUV probes also enable probing the ultrafast electronic response. Here we report on the observation of a prominent electronic response observed from a cobalt film in transmission geometry, when the photon energy is tuned to the ${\mathrm{M}}_{2,3}$ edge of the sample (59.6 eV). The observed dynamics is consistent with a population grating of electronic excitations, which represents the initial step of the EUV TG excitation process and, in a subpicosecond timescale, decays through electron-lattice coupling. On longer timescales, the resulting lattice excitation grating drives the thermoelastic response, regularly observed in EUV TG experiments and featured by acoustic oscillations that modulate the time decay of the lattice temperature grating. The ultrafast electronic relaxation dynamics is no longer observed when the photon energy is largely off resonance, indicating the need for a resonant EUV probe to detect it. While a photon energy scan in a narrow range around the edge does not show sizable changes in the electron-lattice relaxation dynamics, the showcased capability of imposing a nanoscale spatial modulation of the excitation pulse enables the possibility to use a variable EUV TG periodicity to study electronic relaxation dynamics at the nanoscale.

While the valence electron concentration (VEC) of the system ${\mathrm{Cr}}_{20}{\mathrm{Mn}}_{20}$(${\mathrm{Fe}}_{20-x}{\mathrm{Ru}}_x){\mathrm{Co}}_{20}{\mathrm{Ni}}_{20}$ ($0\le x\le 20$), where Fe is partially substituted by Ru, remains at eight electrons per atom (e/a), the structure undergoes a change from single-phase fcc ($x=0$) to a two-phase fcc/hcp system as $x$ increases, with the $\mathrm{VEC}$ of both phases remaining at or very close to 8 e/a. The hcp phase forms already at 5 at% Ru substitution. From studies on thermal expansion determined through x-ray diffraction, magnetization, and Mössbauer spectroscopy, we find that the fcc phase is magnetically active and possesses moment-volume instabilities with energetically close-lying low-spin and high-spin states, while the hcp phase is nonmagnetic in accordance with the predictions of theory. The results show that the hcp phase can be stabilized at a volume fraction of up to 80% under ambient conditions in a predominantly 3-d alloy with $\text{VEC}=8$ e/a.

We study dynamics in classical spin ice following a magnetic field quench to close to the Kasteleyn transition, using Monte Carlo simulations and dynamic scaling theory to characterize the relaxation of the magnetization and the density of magnetic monopoles. We have previously argued that this dynamics can be described in terms of seeding and growth of strings of flipped spins, and our results here demonstrate that a solvable stochastic model based on independent strings correctly describes the relaxation as well as the distribution of string lengths within the critical scaling regime near the transition. We also show how generalized scaling forms capture the behavior over a broader range of monopole densities and provide a clear understanding of the breakdown of the scaling picture further from the critical point.

Owing to the unique coupling effect between spin and topological order, antiferromagnetic topological materials hold significant application prospects in the fields of low-power spintronic devices and quantum computing, emerging as a research focus in the field of condensed matter physics. In this work, the detailed investigation of $\mathrm{C}{\mathrm{r}}_2\mathrm{S}{\mathrm{e}}_3$, a type of antiferromagnetic topological material, was carried out. A combined approach of experimental characterization and first-principles calculations was employed to systematically explore its physical properties and band structure. Experimentally, detailed measurements were conducted on the resistivity, Hall effect, magnetic susceptibility, and heat capacity of $\mathrm{C}{\mathrm{r}}_2\mathrm{S}{\mathrm{e}}_3$, confirming that it exhibits two antiferromagnetic transition temperatures, namely $T_{\mathrm{N}1}\approx 38\mathrm{K}$ and $T_{\mathrm{N}2}\approx 42\mathrm{K}$, which reveals the antiferromagnetic ordered characteristics of the material. Theoretically, the electronic band structure of $\mathrm{C}{\mathrm{r}}_2\mathrm{S}{\mathrm{e}}_3$ was performed via first-principles calculations, providing theoretical support for its topological properties. Our investigations demonstrate that the Hall effect of $\mathrm{C}{\mathrm{r}}_2\mathrm{S}{\mathrm{e}}_3$ can be well fitted by the two-band carrier model; meanwhile, the existence of a possible anomalous Hall effect cannot be excluded, and such a possible anomalous Hall effect is further supported by the results of theoretical calculations. This study expands the investigation of antiferromagnetic topological materials, provides key experimental results for tuning the topological properties of $\mathrm{C}{\mathrm{r}}_2\mathrm{S}{\mathrm{e}}_3$, and offers valuable insights for follow-up research on similar magnetic topological systems.

Motivated by the experimental identification of magnetic compounds consisting of zigzag chains, we analyze the band structure topology of magnons in ferromagnets on a zigzag lattice. We account for the general lattice geometry by including spatially anisotropic Heisenberg exchange interactions and by Dzyaloshinskii-Moriya interaction on inversion asymmetric bonds. Within the linear spin-wave theory, we find two magnon branches, whose band structure topology (i.e., Chern numbers) we map out in a comprehensive phase diagram. Notably, besides topologically trivial and gapless phases, we identify topologically nontrivial phases that support chiral edge magnons. We show that these edge states are robust against elastic defect scattering.