Colossal negative thermal expansion (CNTE) materials are of significant importance for applications in precision engineering and related fields. However, simultaneously achieving a colossal negative thermal expansion coefficient (CTE) and a broad temperature range remains a central challenge. Using a combination of synchrotron x-ray diffraction, Raman spectroscopy, and density-functional-theory calculations, we find that the $A_2{\mathrm{P}}_2{\mathrm{O}}_7$ ($A=\mathrm{Cu}$, Mg, Zn) series exhibits significant CNTE during the α-β phase transition. Structural analysis indicates that during the phase transition, the pronounced contraction of the axial $\mathrm{A}-\mathrm{O}{4}_{\left(\mathrm{long}\right)}$ bonds drives the lattice volume reduction. Meanwhile, temperature-dependent Raman spectroscopy reveals that the 105 $\mathrm{c}{\mathrm{m}}^{-1}$ vibrational mode, assigned to antisymmetric Cu–O bond stretching, undergoes softening accompanied by significant broadening, indicating strong electron–lattice coupling in the series. Combined with energy pathway calculations, the presence of the pseudo-Jahn–Teller effect destabilizes the high-symmetry β phase and drives its transformation into the low-symmetry α phase, thereby leading to significant volume contraction upon heating. Further analysis indicates that the shallow and flattened potential energy surface at the Cu site in ${\mathrm{Cu}}_2{\mathrm{P}}_2{\mathrm{O}}_7$ enables pronounced anti-off-centering displacement of Cu atoms with increasing temperature, which in turn leads to significant NTE before the phase transition, with a volumetric CTE of $-22.25\times {10}^{-6}{\mathrm{K}}^{-1}$. Furthermore, substituting V at the P site leads to the formation of ${\mathrm{Cu}}_2{\mathrm{V}}_2{\mathrm{O}}_7$, which exhibits a colossal negative CTE ($-858.83\times {10}^{-6}{\mathrm{K}}^{-1}$) and a broad CNTE temperature range of 100–900 K. This study not only reveals a physical driving mechanism of CNTE in the $A_2{\mathrm{P}}_2{\mathrm{O}}_7$ series, but also provides important theoretical guidance for the design of novel functional materials that combine colossal negative thermal expansion coefficients with a broad temperature range.

Recent experimental and theoretical studies have suggested a possible Dirac magnon gap in the two-dimensional ferromagnetic semiconductor ${\mathrm{CrSiTe}}_3$. Detailed neutron scattering measurements were performed to shed light on the existence of the magnon gap, and suggest that the gap is very small or nonexistent, with previous measurements being complicated by experimental factors. During these measurements, it was found that the out-of-plane couplings could explain the usual property of the increase in the magnetic transition temperature when ${\mathrm{CrSiTe}}_3$ is exfoliated to monolayers. Furthermore, the material was shown to have anisotropic magnons along the out-of-plane direction, through the proposed Dirac point. We speculate that this is due to an exchange anisotropy, though Kitaev-like interactions alone cannot explain the spectra.

Chiral magnetic textures, such as skyrmions, are of great interest to the condensed matter community due to their novel transport properties. The stabilization of topologically nontrivial magnetic phases, like the skyrmion lattice in cubic MnSi, is governed by underlying magnetic interactions which can be probed via measurements of spin-wave excitations. Here, we report high-resolution inelastic neutron scattering (INS) measurements of the spin waves in Fe-doped ${\mathrm{Mn}}_{0.9}{\mathrm{Fe}}_{0.1}\mathrm{Si}$ deep within its field-polarized ferromagnetic state. We observe nonreciprocal spin waves with a parabolic dispersion that shifts linearly with magnetic field. Crucially, the spin-wave stiffness is highly anisotropic, with values of 17.2(5) meV ${\text{Å}}^2$ parallel to the applied field and 9.3(3) meV ${\text{Å}}^2$ perpendicular to it. While the applied field fundamentally lowers the systems symmetry from cubic to uniaxial, we demonstrate that the induced spin-wave anisotropy is significantly large, which is not captured within the simple theoretical approximations widely applied up to date.

We analyze residual frozen flux in a long narrow superconducting strip cooled through its transition temperature $T_c$ in a small perpendicular magnetic field. This problem is relevant for the issue of trapped magnetic flux in superconducting electronic devices. During cooling, the low-temperature vortex configuration is formed at temperatures very close to $T_c$, where the flux density is determined by dynamic balance between the thermally activated exits and entries of vortices over the geometrical energy barrier formed by the interaction with the strip edges and the Meissner screening current. In the field range between the minimum flux-expulsion field and the penetration field, the equilibrium flux density is finite due to thermal activation and rapidly decreases with decreasing temperature. During cooling, however, the escape rate decreases exponentially, and the vortex density falls out of equilibrium at a field-dependent freezing temperature $T_{\mathrm{fr}}$. We derive and solve the dynamic-balance equation for this process, which yields definite quantitative results for $T_{\mathrm{fr}}$ and the frozen vortex density. The relative freezing temperature $1-T_{\mathrm{fr}}/T_c$ exceeds the fluctuation width of the transition by a large logarithmic factor, rapidly increases when the magnetic field approaches the minimum flux-expulsion field, and logarithmically increases with decreasing cooling rate. The resulting frozen flux density has a very strong magnetic-field dependence, which can be used to define the effective flux-expulsion magnetic field.

The influence of chiral molecular potentials on phase-coherent transport in superconducting Josephson junctions is investigated. Within a Bogoliubov–de Gennes tight-binding framework, a superconducting-normal-superconducting (SNS) junction functionalized by adsorbed chiral molecules is modeled, where electrostatic gradients generated by the molecules induce spin-orbit coupling in the normal region. The equilibrium charge current-phase relation is found to remain largely insensitive to molecular chirality in symmetric, zero-field configurations. In contrast, the spin-polarized equilibrium current exhibits a pronounced chirality-dependent response, with opposite enantiomers producing distinct and anisotropic spin-polarized Josephson currents. The resulting handedness contrast can be enhanced through control parameters such as molecular orientation and the strength of the induced spin-orbit coupling. The temperature dependence of these currents further shows that the chirality-dependent signatures persist across a range of temperatures well below the superconducting critical temperature. These results identify Josephson interferometry as a phase-sensitive setting for probing chirality-dependent spin structure and highlight spin-polarized superconducting transport as a controlled route toward integrating chiral molecular functionality into superconducting spintronic devices.

We analyze the dielectric response of superlattice samples composed of titanate phases: calcium titanate, strontium titanate, and barium titanate, stacked at the ultimate atomic layer limit to break inversion symmetry. High temperature susceptibility measurements extracted from low-frequency ($\sim 100\mathrm{Hz}$) ac capacitance measurements indicate that the asymmetric strain field provides an effective polarizing field that polarizes the samples even at high temperature with the sign of the polarization consistent with the sign of the stacking asymmetry. From the combined temperature, frequency, and electric field dependence, we provide evidence that the size of the dynamically coherent dipole units that persist at high temperatures has little variability from sample to sample and have a volume of $\sim 10$ perovskite unit cells. As temperature is lowered, below a crossover temperature $T_{xy}$ the dielectric response deviates from that expected of activated reorientation of two-state switchable dipoles governed by kinetics. This deviation points to the further growth of dynamically coherent dipole units. Pyrocurrent and dc transient current measurements indicate an unusual asymmetric hysteretic response at low temperatures with a temperature-dependent shift of the $P\left(E\right)$ loops resulting in a low temperature offset polarization. We argue that the responding dipole units above $T_{xy}$ are correlated only along the superlattice stacking direction by the built-in strain field resulting in nanopillars of single unit cell cross-sectional areas. The growth of the dynamically coherent dipole units below $T_{xy}$ points to the emergence of lateral correlations and an unusual ferroelectric response is observed subject to the built-in asymmetric strain field.

Zero-index metamaterials, distinguished by a near-zero effective refractive index, enable extraordinary wave-manipulation capabilities unattainable in conventional media. However, their practical implementation is fundamentally hindered by intrinsic radiative losses, as Dirac-cone modes residing within the light cone inevitably couple to free-space radiation, resulting in severe out-of-plane leakage and propagation attenuation. Here, we theoretically investigate and numerically demonstrate a terahertz metasurface that overcomes this bottleneck by embedding flat-band zero-index modes within topologically protected bound states in the continuum. Through meticulous engineering of the photonic band structure, we tailor an accidental triple degeneracy at the $\mathrm{\Gamma }$ point, forming a Dirac cone intersected by a flat band. The resulting modes simultaneously exhibit an effective zero refractive index, strongly suppressed out-of-plane radiation, divergent photonic density of states, and a polarization vortex singularity with topological charge dictated by the momentum-space topological invariant. We further verify that the topological polarization vortex and the near-zero-index response remain robust under continuous symmetry-preserving structural perturbations, and we assess practical integration feasibility through a substrate-supported configuration. Our findings establish a direct connection among zero-index photonics, topological optics, and flat-band physics, opening up perspectives for achieving low-loss extreme-parameter terahertz photonic platforms.

Charge-density waves (CDWs) are a hallmark of collective electronic ordering. As the pioneering and most fundamental model system studied in CDW physics, one-dimensional (1D) CDWs are theoretically profound yet experimentally fragile. They are widely recognized to be highly susceptible to environmental screening and surrounding lattice bonding. As a result, robust and stable CDWs have thus far been predominantly realized in nearly isolated 1D systems. Here, we demonstrate that robust 1D CDWs can emerge even when the 1D systems are embedded in a two-dimensional metallic environment. Using scanning tunneling microscopy and spectroscopy, we observe clear CDW signatures, including periodic charge modulation and pseudogap formation near the Fermi level, in multiple distinct 1D nanostructures formed in $1T^{\prime }$-phase ${\mathrm{MoTe}}_2$. Our first-principles calculations reproduce the main experimental results, providing strong support for the CDW origin. The consistent observation of these key features across different structural motifs provides unambiguous evidence that CDW order can be robustly stabilized in quasi-1D systems, despite the presence of strong metallic screening and significant surrounding lattice bonding.

Carbon nanotubes (CNTs) constitute a highly tunable platform for probing the interplay between structural chirality and quantum transport in quasi-one-dimensional systems. Here, we perform a systematic study of the nonequilibrium orbital response across a broad set of metallic and semiconducting chiral CNTs. We find that the orbital Edelstein susceptibility depends strongly on both chirality and nanotube diameter, revealing that the orbital response cannot be captured by a universal scaling law. Instead, distinct families of CNTs emerge, forming characteristic orbital-response branches uniquely determined by the chiral wrapping vector. We further investigate the role of metallic contacts on orbital-current generation and orbital selectivity. While metallic CNTs rapidly recover their intrinsic orbital response away from the contact region, semiconducting CNTs display pronounced oscillatory behavior arising from interference between transport channels carrying different angular momenta injected by wide-band metallic contacts. Finally, by incorporating angular correlations into the contact self-energy, we demonstrate that chiral CNTs can operate as efficient orbital angular momentum filters, selectively transmitting orbitally textured electronic states in accordance with the crystal angular momentum of the propagating bands.

The magnetic excitation spectrum of itinerant magnets exhibits rich and complex spectral features that often complicate interpretation of the underlying physics. For perturbations in the long-wavelength limit, one obtains a well-defined pole at zero frequency in the spectral function, the Goldstone magnon. However, for optical modes and finite wave vectors, the magnon spectrum may become damped, exhibit branching, or be completely washed out. In this work, we show how the physical mechanism of all such features can be understood from careful analysis of the eigenmodes of the many-body spectral function. We perform first-principles computations of elemental itinerant ferromagnets using an improved implementation of the linear-response time-dependent density functional theory framework and classify the collective nature of individual spectral features based on the self-enhancement function, the product of the noninteracting Kohn-Sham susceptibility and the exchange-correlation kernel. In particular, we distinguish between coherent and incoherent collective excitations, depending on whether the real part of the self-enhancement function crosses unity at the spectral peak of the magnon, which may or may not be subject to Landau damping as quantified by the imaginary part. Classifying the computed magnon spectra accordingly, we observe coexistence of coherent magnon branches in bcc-Fe, as well as decoherence of the primary magnon branch in fcc-Ni for wave vectors near the Brillouin zone boundary where incoherent valley magnons instead carry substantial spectral weight. The analysis also naturally leads to a definition of the many-body Stoner spectrum and allows us to quantify the binding energy of the Stoner pair excitations.

Strongly correlated fermionic systems are of great interest in condensed matter physics and numerical methods are indispensable tools for their study. However, existing approaches such as exact diagonalization (ED) and stochastic quantum Monte Carlo methods each suffer from fundamental limitations: ED is hindered by exponential scaling in system size, while Monte Carlo methods are plagued by sign problems and long autocorrelation times. These limitations restrict the accessible parameter space and developing algorithms that efficiently alleviate them remains a central challenge in computational physics. In this work, we propose a hybrid algorithm that combines ED and Hamiltonian Monte Carlo (HMC) to simulate two-dimensional (2D) arrays of coupled quantum wires, modeled as interacting fermionic Hubbard chains. We demonstrate how our hybrid implementation of HMC, which we dub ${\mathrm{H}}^2\mathrm{MC}$, outperforms either method alone across several key simulation facets. When compared to pure ED, ${\mathrm{H}}^2\mathrm{MC}$ has a much more favorable computational scaling, which allows us to push simulations to much larger 2D arrays. ${\mathrm{H}}^2\mathrm{MC}$ also greatly alleviates the sign problem and reduces autocorrelation times when compared to pure HMC formulations utilizing either real or imaginary auxiliary fields. Our formalism demonstrates how complementary strengths of seemingly disparate methods can be leveraged to enable feasible simulations in an extended parameter space.

Hall viscosity is a quantized nondissipative stress response of a fractional quantum Hall (FQH) fluid to adiabatic geometric deformations. Despite strong theoretical interest, its experimental observation in the FQH state has remained elusive, making it a demanding target for realization on current IBM quantum hardware. In this letter, we employ a quasi-one-dimensional model of an FQH state coupled to a background metric to probe the geometric response under a metric quench. We design and implement a quantum-circuit protocol that realizes a Hilbert-space-truncated version of the model and extracts the Hall viscosity from the geometric response encoded in the wave-function dynamics on the IBM quantum hardware. While the truncation prevents us from accessing the fully quantized value of Hall viscosity, the hardware data closely track analytical and numerical predictions within this regime.

In this study we present a detailed spectroscopic analysis of the optical gain in a ZnO/ZnMgO waveguide microcavity benchmarked with a thick homoepitaxial ZnO layer. As a prerequisite we perform a precise determination of ZnO excitonic parameters through microreflectivity and low-excitation microphotoluminescence measurements, whose results are used as inputs for the optical gain analysis. While photoluminescence spectra and their dependence on excitation intensity reveal the presence of biexcitons in the ZnO samples, they do not participate in building up optical gain. Instead, three alternative physical processes need to be taken into account to explain optical gain in ZnO: inelastic exciton-exciton scattering; an intermediate regime involving preformed, weak-bond electron-hole Cooper pairs; and an electron-hole plasma at high carrier density. Within the current low quality factor in-plane cavity, our results are consistent with an optical gain at moderate particle densities sustained by a correlated electron-hole phase with preformed electron-hole Cooper pairs. This phase evolves to an electron-hole plasma at larger densities.

We present a rigorous method to reduce the three-dimensional (3D) description of a quantum dot in silicon to an effective two-dimensional (2D) envelope function theory for electron spin qubits. By systematically integrating out the strongly confined vertical dimension using a Born–Oppenheimer-inspired ansatz at the envelope-function level, we derive an effective in-plane potential that faithfully captures the essential electrostatics of the full 3D system. Considering the lowest two eigenstates of the out-of-plane direction, this reduction leads to the natural and explicit emergence of the valley degree of freedom within a 2D formalism, which is derived here from first principles. We validate the accuracy of the method through comparisons with full 3D simulations and demonstrate its superiority over naive 2D slicing, particularly in the presence of interface roughness. Crucially, the reduction in dimensionality leads to substantial computational savings, making our approach particularly well suited for simulating two-electron systems, e.g., for the extraction of parameters such as the exchange coupling. Beyond its practical utility, the rigorous 2D envelope function theory that is introduced in this study incorporates valley physics in a physically grounded manner, offering conceptual clarity on the role of valley states in qubit operation and measurement.

Recent experimental and theoretical studies have revealed the emergence of a linear layer Hall effect (LHE) induced by hidden Berry curvature in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ thin films. This phenomenon underscores the layer degree of freedom as a mechanism for generating Hall transport in layered materials. In this work, we predict a hidden Berry curvature dipole (BCD) in $\mathcal{PT}$-symmetric layered antiferromagnets (AFMs), which manifests as a nonlinear LHE that is even with respect to the AFM order and odd with respect to the vertical electric field, in contrast to the linear LHE. The coexistence of both the hidden BCD and quantum metric dipole (QMD) interprets an asymmetric lineshape with respect to a vertical electric field $E_z$ as observed in recent experiments. Furthermore, we demonstrate that the nonlinear Hall currents induced by the hidden BCD and QMD obey distinct symmetries and flow in different directions, which can be conveniently distinguished through the nonlinear anomalous Hall conductivity. Our proposed nonlinear LHE establishes an experimentally advantageous framework for exclusively probing the hidden BCD quantum geometry.

Magnetic vortices, magnetic textures characterized by their winding numbers of the in-plane magnetization component, hold considerable importance in both fundamental and applied physics. In perpendicularly magnetized disks, transient vortex excitations can be viewed as twisted spin waves, and it is generally considered that their winding numbers should be stable against time evolution. Here, however, we show that this is not the case in systems with discrete rotational symmetry, where a modular transmutation rule applies to the central winding number. We show that such a symmetry breaking can be induced by azimuthal modulation of material parameters in the disk. This work not only advances our understanding of transient vortex excitations, but also establishes symmetry as a novel degree of freedom for manipulating magnetic textures.

We investigate the interplay between photomagnetism and spin-glass freezing in CoFe Prussian blue analogues through controlled reacting time and dynamic magnetic analysis. Reacting time continuously modifies the internal CN-bridged pair populations while keeping the average Fe-vacancy concentration low, thereby providing a route to tune the magnetic exchange network without introducing significant additional defect disorder. Fourier-transform infrared measurements show that the fraction of ${\mathrm{Fe}}^{\mathrm{III}}\text{-CN-}{\mathrm{Co}}^{\mathrm{II}}$ pairs decreases systematically with reacting time, accompanied by an increase in ${\mathrm{Fe}}^{\mathrm{II}}\text{-CN-}{\mathrm{Co}}^{\mathrm{III}}$ pairs. Correspondingly, the ground-state ferrimagnetic response is progressively weakened, as reflected by reduced coercivity, lower high-field magnetization, and a downward shift of the Curie temperature. The spin-glass behavior is suppressed in parallel, with the freezing temperature shifting to lower values and the ac susceptibility peak eventually disappearing in aged samples. Despite this suppression, all samples retain a pronounced photomagnetic response under illumination. Light irradiation enhances the magnetization and coercivity and, more importantly, strengthens or even induces spin-glass freezing in samples with more reacting time. In the defect-poor sample, Mydosh analysis and Vogel-Fulcher fitting show that illumination increases the freezing temperature, the freezing-limit temperature $T_0$, and the activation energy $E_a$, indicating strengthened interaction-dominated freezing and a more stable glassy energy landscape. These results identify ${\mathrm{Fe}}^{\mathrm{III}}\text{-CN-}{\mathrm{Co}}^{\mathrm{II}}$ pairs as the key microscopic units linking photomagnetism to nonequilibrium spin freezing and demonstrate that reacting time and light act as two opposite control parameters on the same exchange network in CoFe Prussian blue analogues.

Several models of the strange-metal state of the cuprate superconductors postulate the existence of strong inelastic forward scattering of the electrons, but direct evidence of such scattering is missing. Here we show that angle-resolved photoemission spectroscopy (ARPES) provides a unique tool that can address this issue. We propose a two-lifetime phenomenological model of the superconducting state of the cuprates, and we show that it explains several salient low-energy features of the measured ARPES spectra. The model enables discrimination between forward- and large-angle scattering and, in addition, gives access to the magnitude of the gap function away from the Fermi surface.