The electron density of states in the open quantum well formed by the downward band bending region at the surface of cesiated $p$-type GaN is investigated. We theoretically predict the existence of metastable resonant states in this nonconfining potential with an intrinsic lifetime around 20 fs. Their experimental observation requires access to the empty conduction band of the cesiated semiconductor, which is possible with near band gap photoemission spectroscopy. The energy distribution of the photoemitted electrons shows contributions coming from electrons accumulated into the resonant states at energies which agree with calculations.

Color centers have been realized in various bulk materials such as diamond and have demonstrated remarkable performance in quantum technologies. However, their applications remain constrained by challenges in photon extraction, precise spatial positioning, and integration into scalable devices. Two-dimensional (2D) materials offer a promising route to overcome these limitations, providing an atomically thin platform well suited for defect engineering. In this work, based on first-principles calculations, we identify multiple types of defects in recently synthesized wide band gap 2D GaN, namely, ${\mathrm{V}}_{\mathrm{Ga}}, {\mathrm{V}}_{\mathrm{Ga}}{\mathrm{C}}_{\mathrm{N}}$, and ${\mathrm{V}}_{\mathrm{Ga}}{\mathrm{O}}_{\mathrm{N}}$, as promising candidates for qubit applications. These defects exhibit well-defined electronic transition pathways within the band gap, with zero-phonon lines located in the visible to near-infrared fluorescence range (697–1000 nm), enabling precise optical excitation. The large transition dipole moment and short radiative lifetime (1.787–14.485 ns) in these defects indicate high photoluminescence quantum yields for single-photon sources. In particular, ${\mathrm{V}}_{\mathrm{Ga}}$ possesses a spin-triplet ground state analogous to the $\mathrm{N}{\mathrm{V}}^{-}$ center in diamond with a zero-field splitting of 2.43 GHz, allowing control via $S$-band microwave radiation. Moreover, the high Debye-Waller factors of ${\mathrm{V}}_{\mathrm{Ga}}$ (0.349) and ${\mathrm{V}}_{\mathrm{Ga}}{\mathrm{O}}_{\mathrm{N}}$ (0.409) indicate strong optical coherence, making them highly suitable for qubit applications. The hyperfine parameters of ${\mathrm{V}}_{\mathrm{Ga}}, {\mathrm{V}}_{\mathrm{Ga}}{\mathrm{C}}_{\mathrm{N}}$, and ${\mathrm{V}}_{\mathrm{Ga}}{\mathrm{O}}_{\mathrm{N}}$ induced by nuclear spins enable the possibility of controlling nuclear spin qubits and offer valuable references for applications such as optically detected magnetic resonance.

Unidirectional acoustic radiation from underwater structures holds significant potential for diverse applications, such as highly directional emission, target detection, and recognition. In this work, we theoretically propose a novel mechanism based on a two-dimensional anisotropic waveguide structure with two radiating channels toward water, which affords anisotropy-induced unidirectional guided resonances (UGRs), in which acoustic radiation is canceled in one of the channels and redirected into the other. We show that the UGRs emerge from the bound states in the continuum when the vertical mirror symmetry is broken by rotating the principal axes of the anisotropic material, and guided by this mechanism, we achieve high up-down radiation ratio. Moreover, we apply temporal coupled mode theory to reveal a unique all-pass acoustic phase-shifting behavior enabled by the UGRs. The proposed anisotropy-induced acoustic UGR mechanism opens new avenues for designing highly directional radiators and phase-shifting devices.

Quantum many-body scars (QMBS) represent a mechanism for weak ergodicity breaking, characterized by the coexistence of atypical nonthermal eigenstates within an otherwise thermalizing many-body spectrum. In this work, we revisit the spin-1 $XY$ model on a periodic chain and construct several new families of exact scar eigenstates embedded within its extensively degenerate manifolds that owe their origins to an interplay of $\mathrm{U}\left(1\right)$ magnetization conservation and chiral symmetries. We go beyond previously studied towers of states and first identify a novel set of interference-protected eigenstates resembling Fock space cage states, where destructive interference confines the wave function to sparse subgraphs of the Fock space. These states exhibit subextensive entanglement entropy, and when subjected to a transverse magnetic field, form equally spaced states whose coherent superpositions display long-lived fidelity oscillations. We further reveal a simpler organizing principle behind these nonthermal states by utilizing the commutant algebra framework, specifically by demonstrating that they are simultaneous eigenstates of noncommuting local operators. Moreover, in doing so, we uncover two more novel families of exact scars: a tower of volume-entangled states, and a set of mirror-dimer states with some free local degrees of freedom. Our results illustrate the power and interplay of interference-based and algebraic mechanisms of nonergodicity, offering systematic routes to identifying and classifying QMBS in generic many-body quantum systems.

Exploring the coexistence of multiple quantum states in two-dimensional materials is a major goal in condensed matter physics. In this study, we theoretically predicted that the quasilayered hexagonal ${\mathrm{V}}_2{\mathrm{N}}_2$ (h-${\mathrm{V}}_2{\mathrm{N}}_2$) monolayer simultaneously hosts metal-insulator antiferromagnetic (AFM) Mott phase transition, higher-order topological insulator (HOTI) state, and tunable in-plane valley polarization (VP) effect. The synergistic effects of temperature modulation of Hubbard parameter ($U$) and force field modulation of hopping integral ($t$) can drive a phase transition from nonmagnetic Dirac metal to AFM Mott insulator, concurrently accompanied by a topological phase transition, which is topologically protected by corner states with a quantized fractional charge in both spin channels. An out-of-plane electric field can break $\mathit{PT}$ symmetry, driving the system into an electric potential difference antiferromagnet with spin-layer-polarized topological corner states. Furthermore, the system exhibits odd-even layer-dependent magnetism with ferromagnetic (FM) and AFM states, enabling effective magnetic control and preserving structural stability until the bulk material (AFM) is reached, providing feasibility for experimental synthesis. Remarkable, different from the conventional FM VP effect with out-of-plane magnetization, we introduce the AFM VP effect with in-plane magnetization in h-${\mathrm{V}}_2{\mathrm{N}}_2$ monolayer to further realize the spin-valley Hall effect, which is governed by $C_2$ symmetry breaking, and can be accurately described by our theoretical model (up to 15.5 meV), providing new ideas for exploring the future valleytronic applications.

Using a combination of time-dependent density matrix renormalization group and single mode approximation, we investigate the dynamical structure factor of spin chains with antiferromagnetic nearest-neighbor $J_1$, next-nearest-neighbor $J_2$, and three-site $J_3$ interactions and show that, in all gapped phases and at the transitions between them, a simple physical picture can be obtained in terms of magnons and spin-1/2 domain-wall excitations or spinons. This applies to the fully dimerized phase, where a magnon mode clearly pops out of the two-spinon continuum for spin-1 and spin-3/2, and to the transition between the dimerized phase and the Haldane phase (resp. partially dimerized phase) for spin-1 (resp. spin-3/2), where spinons are deconfined along the transition but get confined across it when it is first order. Implications for the interpretation of inelastic neutron scattering in spin chains are briefly discussed.

We study finite-size-induced topological phenomena in unconventional superconductors. Specifically, we focus on a thin film with a persistent spin texture, fabricated on a high-$T_{\text{c}}$ cuprate $d_{xy}$-wave superconductors. In two-dimensional $d_{xy}$-wave superconductors, flat-band Andreev bound states appear at the edges. As the system narrows, these bound states acquire an energy gap due to finite-size hybridization and spin-orbit coupling of the persistent spin texture. This induced gap gives rise to the emergence of a topological phase, characterized by an exceptionally large one-dimensional winding number that scales with the film width. We demonstrate the appearance of highly degenerate zero-energy states, leading to anomalous perfect charge transport in dirty superconducting junctions.

${\mathrm{BaAl}}_2{\mathrm{O}}_4$ is a ferroelectric material that exhibits structural quantum criticality through chemical composition tuning. Although theoretical calculations and several diffraction experiments have suggested the involvement of a soft mode in its ferroelectric structural phase transition, direct experimental verification is still lacking. In this study, we successfully observed two soft modes of ${\mathrm{BaAl}}_2{\mathrm{O}}_4$ using x-ray inelastic scattering, providing direct experimental evidence for their role in the structural phase transition. Furthermore, we reveal that the soft modes at the M and K points are nearly degenerate in energy, indicating a delicate balance in which either mode could potentially freeze. The K-point mode simultaneously softens toward the transition temperature ($T_{\mathrm{C}}$) in a manner nearly identical to the M-point mode. However, the phase transition condenses only at the M point, with the M-point mode stabilizing as an acoustic mode in the low-temperature structure and the K-point mode hardening as temperature decreases.

Conductance noise measurements on amorphous films of GeSbTe reveal a structural phase transition driven by temperature. Measurements are performed on samples that were first densified by multiple heat-treatment cycles. In the heavily densified regime, varying the film temperature changed the resistance in a systematic and reproducible way. Monitoring the conductance noise of the sample during temperature cycles, revealed a reversible process. The power spectrum and magnitude of the conductance-noise, measured over the 295–330 K temperature range, exhibited changes that are characteristics of a phase transition. The phases defined in the transition are distinguished by the spectral form and magnitude of their low-frequency fluctuations. This is argued to be a structural order-disorder transition. Raman spectroscopy shows the presence of ${\mathrm{Ge}}_x{\mathrm{Te}}_y$ clusters, confirming previous reports of their high density in the amorphous material, comparable to the crystalline phase. The possible role that these structural motifs play in the observed transport features is discussed.

The precursor phenomenon of phase transitions is widely present in bulk materials, e.g., shape memory alloys, while it rarely observed in two-dimensional materials, especially in kagome lattice compounds $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A$ = K, Rb, Cs). Our calculations with density-functional theory (DFT) indicated that the most stable structural unit of charge density wave (CDW) phases is a $2\times 2\times 2$ supercell (called ${\mathrm{TT}}_{\mathrm{B}}, {\mathrm{TT}}_{\mathrm{C}}$, or ${\mathrm{TT}}_{\mathrm{D}}$ with local twofold symmetry) staggered inverse star-of-David pattern with interlayer $\pi$-phase shift in $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A$ = K, Rb, Cs) compounds. The most stable ${\mathrm{TT}}_{\mathrm{B}}{\mathrm{T}}_{\mathrm{A}}{\mathrm{T}}_{\mathrm{B}}, {\mathrm{TT}}_{\mathrm{B}}{\mathrm{T}}_{\mathrm{A}}{\mathrm{T}}_{\mathrm{C}}$, and ${\mathrm{TT}}_{\mathrm{B}}{\mathrm{T}}_{\mathrm{A}}{\mathrm{T}}_{\mathrm{D}}$ configurations with pseudo-$2c$ stacking are energy-degenerate states in which every bilayer is an order state while the adjacent bilayers may adopt different orientations that lead to a disorder stacking along the out-of-plane direction. They are followed by the ${\mathrm{TT}}_{\mathrm{B}}{\mathrm{T}}_{\mathrm{A}}{\mathrm{S}}_{\mathrm{A}}$ configuration with $2\times 2\times 4$ stacking. The high-temperature metal phase transforms into $2\times 2\times 4$-stack ${\mathrm{TT}}_{\mathrm{B}}{\mathrm{T}}_{\mathrm{A}}{\mathrm{S}}_{\mathrm{A}}$ CDW phase with order-order type upon cooling (theoretically at 66 K for ${\mathrm{KV}}_3{\mathrm{Sb}}_5$), and then into the mixture of pseudo-$2c$-stacking ${\mathrm{TT}}_{\mathrm{B}}{\mathrm{T}}_{\mathrm{A}}{\mathrm{T}}_{\mathrm{B}}, {\mathrm{TT}}_{\mathrm{B}}{\mathrm{T}}_{\mathrm{A}}{\mathrm{T}}_{\mathrm{C}}$, and ${\mathrm{TT}}_{\mathrm{B}}{\mathrm{T}}_{\mathrm{A}}{\mathrm{T}}_{\mathrm{D}}$ CDW configurations with order-disorder type (theoretically at 48 K for ${\mathrm{KV}}_3{\mathrm{Sb}}_5$). A precursor of first-order phase transition occurs (theoretically at 203 and 175 K for ${\mathrm{KV}}_3{\mathrm{Sb}}_5\text{and}{\mathrm{CsV}}_3{\mathrm{Sb}}_5$) upon cooling in $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A$ = K, Rb, Cs) compounds, which comes from the in-plane contraction of vanadium atoms. The strong Fermi surface nesting effect plays a key role in inducing the formation of an in-plane $2\times 2$ CDW superstructure. Our theoretical calculations can not only reasonably explain the phase transition behaviors, but also predict that there are precursor phenomena for kagome lattice compounds $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ ($A$ = K, Rb, Cs) upon cooling.

The Krylov subspace expansion is a workhorse method for sparse numerics that has been increasingly explored as a source of physical insight into many-body dynamics in recent years. In this work we revisit the venerable Anderson model of localization in dimensions $d=1,2,3,4$ to construct local integrals of motion (LIOMs) in Krylov space. These appear as zero eigenvalue edge states of an effective hopping problem in the Krylov superoperator subspace and can be analytically constructed given the Lanczos coefficients. We exploit this idea, focusing on $d=3$, to study the manifestation of the disorder-driven Anderson transition in the anatomy of LIOMs. We find that the increasing complexity of the Krylov operators results in a suppression of the fluctuations of the Lanczos coefficients. As such, one can study the phenomenology of the integrals of motion in the disorder-averaged Krylov chain. We find edge states localized on a vanishing fraction of Krylov space (of dimension $D_K=V^2$ for cubes of volume $V$), both in localized and in extended phases. Importantly, in the localized phase, disorder induces power-law decaying dimerization in the (Krylov) hopping problem, producing stretched exponential decay of the LIOMs in Krylov space with a stretching exponent $1/2d$. Metallic LIOMs are completely delocalized albeit across only $\propto \sqrt{D_K}$ states. Critical LIOMs exhibit power-law decay with an exponent matching the expected value of 0.29.

Materials with heavier constituents typically exhibit lower lattice thermal conductivity (${\kappa }_L$). Herein, we report an anomalous trend in orthorhombic $\mathrm{Ba}M{\mathrm{S}}_3$ ($M=\mathrm{Zr}$, Hf) chalcogenide perovskites, where heavier ${\mathrm{BaHfS}}_3$ shows a higher ${\kappa }_L$ than ${\mathrm{BaZrS}}_3$. Our first-principles approach, which incorporates temperature-dependent force constants, enables us to trace this anomaly to the competition between the mass effect and the lanthanide contraction effect. While the former reduces phonon group velocities in ${\mathrm{BaHfS}}_3$, the latter strengthens chemical bonding, suppresses lattice anharmonicity, and thus elongates phonon lifetimes. The resulting reduction in phonon-phonon scattering overcompensates the velocity reduction, leading to the enhanced ${\kappa }_L$ in ${\mathrm{BaHfS}}_3$. Our finding provides insights into the interplay of mass effect and lanthanide contraction effect of compounds with postlanthanide elements, which also guides the exploration of materials for thermoelectric and thermal barrier coating applications.

We study quantum quench dynamics in ($1+1$)-dimensional critical systems, starting from thermal pure states called crosscap states, and evolving them under spatially inhomogeneous Hamiltonians. The spatial inhomogeneity is introduced through a deformation of the Hamiltonian, expressed as linear combinations of the generators of the ${\mathrm{SL}}^{\left(q\right)}(2,\mathbb{R})$ subalgebra of the Virasoro algebra. We analyze the free massless Dirac fermion theory and holographic conformal field theory as prototypical examples of integrable and nonintegrable dynamics. Consistent with general expectations, “Möbius-type” deformations lead to thermalization in the nonintegrable case, and to periodic revivals in the integrable one. In contrast, “sine-square-type” and “displacement-type” deformations prevent both thermalization and scrambling, instead producing late-time, graphlike entanglement patterns. These patterns emerge from the interplay between the deformed Hamiltonian and the crosscap initial state and appear to be universal: they are determined solely by the deformation profile while remaining largely insensitive to microscopic details. Finally, we perform a holographic calculation in three-dimensional gravity using the ${\text{AdS}}_3/{\text{CFT}}_2$ correspondence, which reproduces the main features of our ($1+1$)-dimensional study.

The diverse nodal spin structures in $d/g/i$-wave altermagnets (AMs) may cause distinct light-induced spin responses yet remain poorly understood. Using real-time time-dependent density functional theory, we reveal that laser-induced ultrafast demagnetization dynamics in the $g$-wave AM CrSb are strongly governed by the laser incidence direction. Under normal incidence along the [0001] axis, two Cr sublattices exhibit symmetric temporal demagnetization but with different amplitudes, preserving the zero net magnetization—unlike the behavior in $d$-wave AM. Off-normal incidence, however, induces pronounced asymmetric demagnetization between sublattices, transiently driving the system into a ferrimagnetic state with a sizable net magnetization. Such incidence-dependent magnetization dynamics arises from the characteristic nodal structures in bulk $g$-wave AM's electronic structure, which enable anisotropic optical-induced intersite spin transfer. By comparing $g$-wave and $d$-wave AMs, we propose that light-induced magnetization arises when laser polarization aligns with spin-uncompensated regions in electronic structures. This can be readily determined from the local spin density of states along specific band paths. Our results provide a fundamental understanding of laser-induced ultrafast dynamics in AMs.

The pairing mechanism in infinite-layer nickelates (${\mathrm{RNiO}}_2$) remains highly debated. Conventional density functional theory (DFT) predicts a weak electron-phonon coupling (EPC) that fails to account for the observed superconducting transition temperatures ($T_c$), but such estimates are limited by the well-known inability of DFT to capture strong electronic correlations. Here, we develop a consistent theoretical framework combining DFT with the GW method to quantitatively assess the electron-phonon coupling (EPC) strength across the nickelate series (R = La, Nd, Sm), and predict a novel actinide analogue (R = Ac). Our calculations reveal that $\mathit{GW}$ self-energy effects substantially renormalizes the interstitial states and rare-earth $d$ bands, bringing them closer to the Fermi level and dramatically enhancing EPC. This enhancement follows a clear monotonic trend from La to Sm, driven by a cooperative chemical-pressure mechanism (lanthanide contraction) that simultaneously increases the electronic density of states and hardens the relevant phonon modes. This synergy is consistent with the experimentally observed rise in $T_c$ and optimizes the high $T_c$ in ${\mathrm{SmNiO}}_2$. Extending this framework, we predict ${\mathrm{AcNiO}}_2$ as a promising actinide analogue with moderate EPC, providing a critical testbed for disentangling the respective roles of the rare-earth $d$ and interstitial-$s$ orbitals. Our work suggests EPC as a sizable and systematically tunable contributor to superconductivity in nickelates and offers a quantitative bridge between theory and experiment within our $\mathit{GW}$ framework, particularly regarding the critical role of interstitial states and chemical pressure, as recently revealed by angle-resolved photoemission spectroscopy.

We present a self-consistent theory to calculate the static and uniform spin susceptibility in superconductors under simultaneous Zeeman magnetic fields and Rashba-type spin-orbit coupling (SOC). Employing a single-band Bogoliubov-de Gennes Hamiltonian, we solve the gap equation for both conventional $s$-wave spin-singlet and six representative $p$-wave spin-triplet pairing states, categorized into opposite-spin-pairing (OSP) and equal-spin-pairing (ESP) classes. The Kubo formula, decomposed into intra- and interband particle-hole and particle-particle channels, provides two key constraints: At zero temperature, only particle-particle terms contribute, while at the critical temperature $T_c$, only particle-hole terms remain, ensuring $\chi \left(T_c^{-}\right)={\chi }_N$ for continuous phase transitions. For $s$-wave pairing, a Zeeman field reduces $T_c$, whereas Rashba SOC preserves $T_c$ but yields a residual zero temperature spin susceptibility $\chi \left(0\right)$ which approaches $2{\chi }_N/3$ in the strong SOC limit; combined fields create a Bogoliubov Fermi surface, resulting in a kink in $\chi \left(0\right)$. In contrast, $p$-wave states exhibit strong anisotropy: OSP states mimic spin-singlet pairing behavior for parallel Zeeman fields and ESP for transverse ones, while ESP states show the opposite, with Rashba SOC potentially changing the quasiparticle nodal structure, lowering $T_c$, or causing ${\chi }_{zz}\left(0\right)$ divergences. This framework offers quantitative benchmarks for Knight-shift experiments in non-centro-symmetric superconductors like $A_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ ($A$ = Na, K, Rb, and Cs), enabling diagnostics to disentangle pairing symmetry, SOC strength, and Zeeman effects.

Bound states in the continuum (BICs) and surface lattice resonances (SLRs) can both provide in-plane optical feedback for lasing while enabling surface emission. However, in Bravais lattices composed of symmetric dielectric nanoparticles, lasing is typically observed only from BICs, as SLRs suffer from relatively large radiative losses and fail in the competition for gain. By introducing size detuning into a Bravais lattice, the guided modes of the original Bravais lattice are folded into the light cone of the resulting non-Bravais lattice. Among the modes within the light cone, BICs retain the same symmetry-protected characteristics as those in a Bravais lattice, whereas the quality factor of SLRs can be tuned by adjusting the extent of size detuning. We fabricated non-Bravais lattices of ${\mathrm{TiO}}_2$ nanoparticles on quartz substrates and integrated them with dye molecules as the gain medium. Lasing modes were identified via angle- and polarization-resolved measurements. We observed that lasing from SLR and BIC modes emerged simultaneously, with comparable threshold values.