Chiroptical planar metasurfaces have become a promising platform for exploring chirality-based applications and functionalities in nanophotonics due to their capability to enhance light-matter interactions at the nanoscale. Most existing research experiences an inverse correlation between quality factor ($Q$-factor) and circular dichroism (CD) that involves the copolarized (${\mathrm{CD}}_{\mathrm{Chi}}$) and cross-polarized (${\mathrm{CD}}_{\mathrm{Ani}}$) components, thereby limiting the practical applications of multifunctional and tunable optical sensing capabilities. Here planar chiral silicon metasurfaces, incorporating $\mathsf{I}$-shaped and $\mathsf{L}$-shaped meta-atoms, are numerically demonstrated and employed to yield a positive correlation between the $Q$-factor and CD, as well as reveal high-$Q$ and ultrasensitive chiral sensing in the near-infrared regions. In particular, leveraging distinct symmetry-breaking approaches, the $Q$-factor, ${\mathrm{CD}}_{\mathrm{Chi}}$, and ${\mathrm{CD}}_{\mathrm{Ani}}$ exhibit positive correlation with the related asymmetry parameters. Moreover, by embedding with the phase-change material ${\mathrm{VO}}_2$, dynamic modulation of ${\mathrm{CD}}_{\mathrm{Chi}}$ and ${\mathrm{CD}}_{\mathrm{Ani}}$ can be finely adjusted via varying the configurations and the thickness of the ${\mathrm{VO}}_2$. In addition, the steerable chiroptical responses can be engineered to achieve high-$Q$ and ultrahigh-sensitivity chiral sensing in the near-infrared regions. These findings not only provide a unique approach for the realization of high-$Q$ and ultrasensitive metadevices but promote the advancement of multifunctional biochemical and environmental sensing applications.

Flat-band (FB) systems originating from special lattice geometry like in kagome metals as well as localized orbitals in materials such as heavy-fermion (HF) compounds have attracted intensive interest due to their band topology and strong electron correlation effects, leading to emergent quantum states of matter. However, how these two distinct types of FBs coexist and interact within a single material remains largely unexplored. Here, we report that ${\mathrm{YbCr}}_6{\mathrm{Ge}}_6$, hosting both a Cr kagome lattice and localized Yb $4f$ electrons, exhibits HF behavior and has an antiferromagnetic ground state with a transition temperature $T_N$ = 3 K. Angle-resolved photoemission spectroscopy (ARPES) reveals the coexistence of Cr kagome-derived and Yb $4f$-derived FBs near the Fermi level $E_{\mathrm{F}}$. Photon-energy-dependent ARPES measurements distinguish the bulk dispersive kagome-derived bands from the nearly momentum-independent Yb $4f$ states, while clear spectroscopic signatures of $c\text{−}f$ hybridization are observed between the Yb $4f$ FBs and kagome-derived conduction bands. The high density of states associated with the Cr kagome FB and the $c\text{−}f$ hybridization provide microscopic insight into the enhanced electronic correlations and magnetic ordering in ${\mathrm{YbCr}}_6{\mathrm{Ge}}_6$. Our findings establish ${\mathrm{YbCr}}_6{\mathrm{Ge}}_6$ as a promising platform for exploring the interplay between kagome FB physics and strong $f$-electron correlations.

The geometric analogs of Bloch oscillations studied so far have relied on Berry curvature. We show that a weakly inhomogeneous electric field adds a distinct quantum-metric term to semiclassical wavepacket dynamics, generating an oscillatory real-space contribution even when the Berry curvature vanishes. The associated transport response comprises an intrinsic and a scattering-time-dependent part. In the regime studied, the latter can dominate and approach finite saturation at high field when the relative field inhomogeneity is held fixed. A tilted Dirac model illustrates the mechanism. Realistic platforms will likely require synthetically engineered superlattices, with a finite quantum metric and an adequate band gap.

The interplay between crystal symmetry and electron-phonon coupling is crucial for understanding thermal transport in two-dimensional materials. Using first-principles calculations combined with Wannier interpolation and coupled electron-phonon Boltzmann transport theory, we investigate how inversion-symmetry breaking affects the electronic structure, phonon spectrum, and thermal conductivity of monolayer ${\mathrm{Ta}}_2{\mathrm{CS}}_2$. We find that the symmetric structure is metallic, whereas the asymmetric structure is semiconducting with a narrow band gap. In the symmetric structure, electrons contribute about 40% of the total thermal conductivity at 300 K. In contrast, in the asymmetric structure the electronic contribution becomes negligible, while electron-phonon coupling strongly suppresses phonon heat transport under carrier doping. At 300 K and a carrier concentration of ${10}^{14} {\mathrm{cm}}^{-2}$, the lattice thermal conductivity decreases from $103.5\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ to 15.7 and $7.3\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ for hole and electron doping, respectively. Symmetry analysis indicates that inversion-symmetry breaking relaxes the selection rules and opens additional scattering channels, while the accompanying charge redistribution increases the electron-phonon matrix elements, together leading to enhanced phonon-electron scattering. Our results demonstrate that symmetry breaking can strongly modify electron-phonon coupling and the associated thermal transport, highlighting symmetry control as an effective strategy for tuning heat conduction in two-dimensional polar materials.

Two-dimensional (2D) Janus WSSe has attracted considerable attention for optoelectronic device applications due to its unique structural asymmetry and exceptional electronic and optical properties. However, intrinsic defects inevitably introduced during experimental growth can significantly modulate its material properties and device performance. In this work, first-principles calculations were performed to systematically investigate the impacts of vacancies, interstitials, and antisite defects on the geometric structure and electronic properties of a Janus WSSe monolayer. Furthermore, the roles of sulfur vacancies (${\mathrm{V}}_{\mathrm{S}}$) and selenium vacancies (${\mathrm{V}}_{\mathrm{Se}}$) in modulating the electronic and optical properties of the 2D ZnO/WSSe van der Waals heterostructure were explored. In the isolated two-dimensional 2H-WSSe monolayer, although ${\mathrm{V}}_{\mathrm{S}}$ and ${\mathrm{V}}_{\mathrm{Se}}$ defects are identified as deep-level defects, the calculated carrier capture coefficients and capture cross sections reveal that they do not act as effective nonradiative recombination centers. Regarding the ZnO/WSSe heterostructure, the introduction of ${\mathrm{V}}_{\mathrm{S}}$ and ${\mathrm{V}}_{\mathrm{Se}}$ narrows the band gap, enhances low-energy light absorption, and modulates interfacial charge transfer without disrupting the heterostructure stability. This work provides a solid theoretical foundation for defect engineering in WSSe-based materials and the design of high-performance ZnO/WSSe heterostructure optoelectronic devices.

Hard-x-ray C $1s$ photoemission from monolayer graphene probes a regime in which nuclear recoil and intrinsic electronic asymmetry contribute on comparable energy scales to the observed spectral line shape. Here we combine experiment and modeling over the photon-energy range $0.8–8\mathrm{keV}$ to resolve this interplay quantitatively. A graphene-specific implementation of the Fujikawa-Takata cumulant formalism, based on an anisotropic vibrational density of states constrained by first-principles phonon calculations, captures the expected recoil scaling with photon energy and emission geometry but fails to reproduce the pronounced asymmetric tails of the measured spectra. To overcome this limitation, we introduce an explicit electronic convolution model in which a photon-energy-independent reference response, dominated by the electronic line shape and extracted from the low-recoil $0.8\mathrm{keV}$ data through a recoil-inclusive fit, is convolved with a phonon recoil kernel carrying the full dependence on photon energy and emission angle. This approach reproduces both the measured line-shape evolution and the observed peak shifts across the explored energy range without refitting the spectra at higher photon energies. The results show that recoil in graphene cannot be described by a baseline treatment in which the phonon recoil kernel is combined only with symmetric lifetime broadening, but must be treated together with the intrinsic many-body electronic response of the C $1s$ line.

Materials containing unreactive elements are attracting increasing attention for their unexpected characteristics such as pressure-driven superconductivity. However, the known helium-incorporating superconductors (HISCs) are constrained by extreme compression, and thus achieving high-temperature superconductivity in helium-based compounds under moderate pressure is a key challenge. Here, we conducted a comprehensive study of the ${\mathrm{Na}}_2\mathrm{He}$-B system, leveraging a first-principles-assisted configuration prediction method, and presented two previously unknown stable phases, encompassing $P{6}_3/mmc {\mathrm{Na}}_2{\mathrm{HeB}}_2$ and Immm ${\mathrm{Na}}_2{\mathrm{HeB}}_7$. In particular, ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ manifests a prototype hexagonal layered structure featuring interlayer sodium-helium co-insertion and a honeycomb-shaped covalent boron grid. Remarkably, calculations of electron–phonon coupling (EPC) uncover that, among HISCs, ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ holds the highest superconducting transition temperature ($T_c$) at a low pressure of 20 GPa, reaching 38 K, which is primarily attributed to the coupling between in-plane B $2p$ electronic states at the Fermi level and Na- and He-governed low-frequency phonon modes. In contrast, the strategy of enhancing the EPC strength through electronic doping ($-0.04e$/cell) enabled ${\mathrm{Na}}_2{\mathrm{HeB}}_2$ to exhibit high-$T_c$ behavior at 42 K. These findings provide important implications for the discovery of additional superconductors composed of inert elements.

We study a finite Floquet chain in which a uniform nearest-neighbor hopping coexists with a periodically rotating, SU(2)-dictated spin-assisted hopping profile. The resulting coupling is spatially inhomogeneous—weakest at the chain boundaries and strongest in the bulk—and produces a frequency-dependent Floquet-Sambe bottleneck. In the closed system, the mean inverse participation ratio of the Floquet eigenstates exhibits a striking nonmonotonic dependence on the driving frequency $\omega$: the states remain extended at both low and high frequencies, but become maximally localized at an intermediate frequency. We demonstrate that this localization maximum occurs at ${\omega }_{\mathrm{peak}}\sim {\mu }_{-s}=\sqrt{2s}$, a scale controlled by the first boundary bottleneck. To connect these spectral properties to measurable transport, we construct an open-system Floquet-Sambe Green's-function inverse participation ratio from the spatial density of the injected scattering state. This open-system diagnostic recovers the same nonmonotonic localization trend as its closed-system counterpart, with the peak shifted to higher frequencies by the static bandwidth and the lead self-energy. These findings establish the driven synthetic spin chain as a directly realizable, frequency-tunable platform for coherent information storage and retrieval, rooted in the interplay of Floquet-Sambe virtual channels, boundary-controlled localization, and frequency-selective transport in emerging multilevel superconducting circuit architectures.

Motivated by intriguing properties of geometrically frustrated systems, in the present work, another member of the triple perovskite family, ${\mathrm{Ca}}_3{\mathrm{CoSb}}_2{\mathrm{O}}_9$, with a ${\text{Co}}^{2+}$ triangular motif, has been synthesized, and its structural, magnetic, and thermal transport properties were studied in detail. The triple perovskite crystallizes in the monoclinic phase with a $P{2}_1/c1$ symmetry. A cusp in the dc magnetic susceptibility, accompanied by a $\lambda$-like feature in the ac susceptibility and specific heat, indicates a transition to an antiferromagnetic state below $T_N\sim 3.8\text{K}$. Magnetic susceptibility measurements confirm the existence of the ${\mathrm{Co}}^{2+}$ moments with $S=1/2$ spin state, a large Curie-Weiss temperature of ${\theta }_{\text{CW}}=-76.70\text{K}$, and a significant degree of magnetic frustration ($f=|{\theta }_{\text{CW}}/T_N|\approx 20$). The temperature-dependent ac magnetization reveal a prominent peak at $T_N$ that exhibits characteristic magnitude suppression and a subtle shift (3.8 to 4.1 K) with increasing frequency from 0.21 to 631 Hz. Additionally, a nondispersive kink at $T\sim 7.0\text{K}$ was observed, indicative of persistent short-range magnetic correlation above $T_N$. Moreover, the absence of a spin-flop transition or a $M_s/3$ magnetization plateau in field-dependent studies up to $16\text{T}$, suggests that the structural distortions in ${\text{Ca}}_3{\text{CoSb}}_2{\text{O}}_9$ stabilize a noncollinear ${120}^{\circ }$ spin structure against field-induced quantum phase transitions.

In this work we study the stabilization of the orthorhombic phases in small $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles (average size ∼7 nm) annealed under different oxygen partial pressures. Concentration of the oxygen vacancies, which is determined by annealing conditions, was estimated from the electron paramagnetic resonance spectra and x-ray photoelectron spectroscopy. The fraction of the orthorhombic phases, that is determined by the x-ray diffraction and nuclear magnetic resonance, depends on the concentration of oxygen vacancies. Phenomenological calculations based on Landau-Ginzburg-Devonshire theory considering trilinear coupling between nonpolar, antipolar, and polar phonon modes, indicate that chemical strain induced by oxygen vacancies can stabilize the orthorhombic o-III phase with the ferroelectric long-range ordering in small $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles. The theory confirms the stability of ferroelectric polarization in the vacancy-enriched $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles. The increase in the intensity of the dielectric permittivity maximum observed near 350–380 K in a PVDF matrix embedded with $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles annealed in the $\mathrm{CO}+{\mathrm{CO}}_2$ atmosphere is clearly associated with an increase in oxygen vacancy concentration. The vacancies lead to defect-induced elastic dipole formation and an increase in ionic conductivity, which decreases the depolarization field and may induce the ferroelectric-like phase transition in the vacancy-enriched $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles. Due to the interfacial effects, the negative capacitance states may be realized in weakly screened and spatially isolated $\mathrm{H}{\mathrm{f}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}{\mathrm{O}}_2$ nanoparticles embedded in the PVDF matrix. The present approach based on oxygen-vacancy-induced elastic and screening effects may provide a route for engineering ferroelectric-like states in other nanoscale ferroic oxides.

We study the entanglement entropy (EE) of the one-dimensional transverse-field quantum Ising chain (QIC) and the XX (isotropic XY) chain under various boundary conditions (BCs). We numerically calculate the EE for a system of size $L$ and a subsystem of size $l$ at the critical point. Five BCs are considered: periodic, free-free, fixed-fixed $(+,+)$ and $(+,-)$, and fixed-free. We also employ exact solutions and conformal field theory (CFT) predictions, which yield results highly consistent with our numerical data. In our numerical approach, we apply the Jordan-Wigner transformation to map the spin chain to a system of spinless fermions and compute their correlation functions, from which the EE is subsequently derived. The EE is calculated for 19 different subsystem fractions, fixing $l/L$ at values of $1/20,2/20,\cdots ,19/20$ for each case. All numerical computations are performed using quadruple precision to ensure accuracy. We observe even-odd oscillations in the EE of the XX chain under free-free, fixed-fixed $(+,+)$, fixed-fixed $(+,-)$, and fixed-free BCs. We then fit the calculated EE using finite-size scaling expansions in terms of $L^{-n}$ and $L^{-n}lnL$ for each corresponding case. The fitted parameters for the leading $lnL$ term and the constant term are found to coincide with CFT predictions to very high accuracy. For periodic BCs, the parameter for the $L^{-2}$ correction term as a function of $l/L$ is consistent with the conjecture by Calabrese et al. Furthermore, we conjecture the form of the $L^{-4}$ correction and analytically calculate its leading term using random matrix theory. For the XX chain with free-free BCs, we verify the relationship between the coefficient of the $L^{-1}$ term and $l/L$ extracted from the formula conjectured by M. Fagotti et al., [J. Stat. Mech. (2011) P01017] and we obtain conjectured closed-form expressions for the coefficients of the $L^{-2}, L^{-3}$, and $L^{-4}$ terms, which are supported by high-precision numerical fitting and partial analytical arguments. Utilizing the relationship between free-free and $(+,+)$ BCs, we determine the form of the coefficients for the $L^{-2}$ and $L^{-4}$ terms in the XX chain with $(+,+)$ BCs. Consequently, we obtain first four parts of the alternating term in the EE for the XX chain under free-free and $(+,+)$ BCs. For the EE of the first excited state in the QIC with free-free BCs, we conjecture the exact form of the $L^{-1}$ correction term, which coincides perfectly with our numerical results. For the QIC with fixed-free BCs, we calculate the perturbation expansion around $l/L=0$ and 1 for the correction term stemming from the Ising CFT. Finally, inspired by the resonating valence bond (RVB) picture introduced by N. Laflorencie et al., [Phys. Rev. Lett. 96, 100603 (2006)] we discuss the EE oscillations in the XX chain under the four aforementioned BCs qualitatively.

Altermagnets combine compensated collinear magnetic order with momentum-dependent spin splitting. A key question is how such spin splitting can arise from electronic interactions in a spin-degenerate Dirac semimetal and what spin-resolved transport signatures it produces. We address this issue using a staggered $\pi$-flux Hubbard model. Within a homogeneous, collinear, two-sublattice self-consistent Hartree-Fock ansatz, we show that the Hubbard interaction drives the Dirac semimetal into an altermagnetic phase with an even-parity, $d_{xy}$-wave spin splitting protected by mirror-spin symmetry $\left[C_2\right|\left|M_y\right]$. The interaction-generated order gaps the Dirac cones at half filling and gives rise to an altermagnetic metal upon doping. In the spin-orbit-free limit, we compute the second-order electric and thermoelectric responses and identify a clear channel dependence. The nonlinear charge Hall and Nernst responses are already permitted in the spin-degenerate semimetal and are further reshaped by the interaction-driven Fermi-surface reconstruction, making them nonunique indicators of altermagnetic order. By contrast, the nonlinear spin Hall and spin Nernst responses vanish identically in the identical-spin-block parent and become finite in the pure-spin $yxx$ channel of the ordered state, accompanied by a characteristic sign reversal across half filling. The mirror-spin symmetry produces an orthogonal pure-charge $xyy$ channel and opposite domain parities. These results establish a symmetry-resolved two-channel nonlinear transport diagnostic based on the parent-state null and directional charge-spin separation.

In this study, we investigate coherent exciton dynamics in a thin GaAs film using three-beam four-wave mixing (FWM) techniques. The GaAs film exhibits spatially varying biaxial tensile strain, enabling us to study the influence of differing strain on the dephasing time of strain-split heavy- and light-hole excitons. Heterodyne FWM experiments reveal an essentially homogeneously broadened exciton polarization throughout the film. While the exciton dephasing rates show no discernible correlation with the local strain variations, excitation-induced dephasing becomes the dominant FWM generation process at long dephasing times. Under cross-linear excitation the FWM signal mainly originates from two-exciton correlations. Theoretical analysis using the ten-level optical Bloch equations substantiates these findings. The strain resilience of the picosecond-scale exciton dephasing time suggests GaAs films as a powerful platform for investigating coherent light-matter interactions and coupling in composite exciton-plasmon quantum systems.

By employing a combined method of density functional theory and dynamical mean field theory $(\mathrm{DFT}+\mathrm{DMFT})$ we investigate the effect of electronic correlations on the magnetic and superconducting properties of the iron-based parent compound LaFeAsO. We find that the static nonlocal susceptibility $\chi \left(\mathbf{q}\right)$ and the dynamical spin structure factor $S(\mathbf{q},\omega )$ exhibit a peak at the in-plane wave vector $\mathbf{Q}=(\pi ,\pi )$, which is strongly enhanced upon inclusion of dynamical vertex corrections in the ladder approximation, leading to magnetic instability. Considering the eigenfunctions of the Bethe-Salpeter equation with the vertex, obtained within the second-order perturbation theory, as well as the ladder approach containing dynamic interaction vertices, we obtain a close competition between $d$-wave and $s_{\pm }$ order parameters, dominating in the second-order and ladder approach, respectively. We argue that the dominating $s_{\pm }$ instability in the ladder $\mathrm{DFT}+\mathrm{DMFT}$ approach is related to the reduced degree of magnetic frustration by itinerant degrees of freedom due to only partially formed local magnetic moments. Our study shows that dynamic correlation effects do not change the type of leading superconducting instability in LaFeAsO.

Optically addressable valley degrees of freedom in transition-metal dichalcogenide heterostructures provide a powerful platform for valleytronic and quantum-optical functionalities. In moiré superlattices, interlayer excitons inherit valley-contrasting optical selection rules while acquiring long lifetimes, electric dipoles, and site-dependent optical responses. However, because conventional measurements typically probe time-integrated valley polarization, the dynamical origin of vanishing polarization has remained elusive. Here, we show that a nearly zero steady-state valley polarization in electrically tunable moiré excitons does not necessarily indicate fast valley relaxation. Helicity-resolved time-resolved photoluminescence reveals a temporal crossing between ${\sigma }^{+}$ and ${\sigma }^{-}$ emission, indicating that helicity-opposite dynamical components coexist and compensate after time integration. A minimal two-channel model, representing A-like and B-like moiré emission channels with opposite optical selection rules and distinct effective decay/depolarization rates, reproduces the observed helicity crossing without invoking a single rapid valley relaxation process. Furthermore, the crossing time evolves systematically with electrostatic tuning, demonstrating that the hidden valley dynamics are electrically controllable. These results show that time-integrated circular polarization can give a false-negative indication of valley polarization in multichannel valley emitters.

We present a model for interacting electrons in a continuum band structure that resembles a trash can, with a flat bottom of radius $k_b$ beyond which the dispersion increases rapidly with velocity $v$. The form factors of the Bloch wave functions can be well-approximated by the Girvin-MacDonald-Platzman algebra, which encodes the uniform Berry curvature. We demonstrate how this model captures the salient features of the low-energy Hamiltonian for electron-doped pristine $n$-layer rhombohedral graphene ($\mathrm{R}n\mathrm{G}$) for appropriate values of the displacement field, and we provide corresponding expressions for $k_b$. In the regime where the Fermi wave vector is close to $k_b$, we analytically solve the Hartree-Fock equations for a gapped Wigner crystal in several limits of the model. We introduce a new method, the sliver-patch approximation, which extends the previous few-patch approaches and is crucial in both determining the full Chern number (beyond mod 3) of the ground state and gapping the Hartree-Fock solution. A key parameter is the Berry flux ${\phi }_{\text{BZ}}$ enclosed by the (flat) bottom of the band. We analytically show that there is a ferromagnetic coupling between the signs of ${\phi }_{\text{BZ}}$ and the Chern number $C$ of the putative Wigner crystal. We also study the competition between the $C=0$ and 1 solutions as a function of the interaction potential for parameters relevant to $\mathrm{R}n\mathrm{G}$. By exhaustive comparison to numerical Hartree-Fock calculations, we demonstrate how the analytic results capture qualitative trends of the phase diagram, as well as quantitative details such as the enhancement of the effective velocity. Our analysis paves the way for an analytic and numerical examination of the stability and competition beyond mean-field theory of the Wigner crystals in this model.

Binding energy, which quantifies pair formation, is a key factor in the emergence of superconductivity. Here, we show that even when multiple spins are complexly coupled, hole-doped systems can be mapped, in the strong-binding-energy limit, onto an effective hardcore boson model equivalent to the XXZ model, and exhibit promising signatures of superconductivity. We demonstrate this theory analytically and numerically in the double Kondo lattice model. Using the density-matrix renormalization group method, we show that a pairing state is maintained via a crossover even for parameters away from the strong-coupling regime. Additionally, we find that once binding energies are sufficiently generated, pair correlations develop similarly regardless of the details of local spin correlations. Our findings provide useful insights into the mechanism of superconductivity.