We experimentally demonstrate boundary-induced helical bulk states (BI-HBSs) for rf acoustic transport in LiNbO3 thin-film phononic crystals ($\sim 175-200\mathrm{MHz}$). A boundary-symmetry selection rule at an accidental $\mathrm{\Gamma }$-point fourfold degeneracy creates interior bulk channels that couple to wide-aperture interdigital transducers without edge-aperture mismatch. Near-field vibrometry and two-port rf $S$ parameters confirm low-loss propagation with strongly suppressed backscattering through wavelength-scale defects. The helical band also provides slow-wave, low-dispersion delay and phase control on chip.

Heat waste is a bottleneck in the development of green information technologies and much effort has been devoted to suppress the heating effect in both electronic and spintronic devices. Here, we take an alternative approach and show that controllable heating at the nanoscale can actually benefit information processing. In particular, we study a hybrid nanostructure consisting of a metallic square frame and an antiferromagnetic (AFM) thin film and show that the plasmonic heating can reversibly switch two perpendicularly oriented AFM domains without the assistance of magnetic fields and electric currents. The required switching energy is at the order 1 nJ, 3 to 6 orders of magnitude lower than the current-driven AFM switching. The physical mechanism arises from the thermal-induced strain fields inside the frame, which couple to and manipulate the magnetic orientation via magnetoelastic effect. The strain field direction can be well controlled by selectively exciting the longitudinal and transverse plasmon modes by varying the polarization of the waves, which readily allows for a reversible switching of the AFM vector. Our findings provide tremendous opportunities for optically manipulating the magnetism with ultralow energy consumption and may further promote the interdisciplinary study of photonics, acoustics, and spintronics.

Photoexcitation has been utilized to control quantum matter and to uncover metastable phases far from equilibrium. Among demonstrations to date, the most common is the photoinduced transition from correlated insulators to metallic states; however, the reverse process without initial orders has not been observed. Here, we show ultrafast metal-to-insulator transition in gate-doped ${\mathrm{WS}}_2/{\mathrm{WSe}}_2$ and ${\mathrm{WSe}}_2/{\mathrm{WSe}}_2$ moiré devices using photothermionic hole injection from graphite gates. The resulting correlated insulators are metastable, with lifetimes exceeding microseconds. These findings establish an effective mechanism for the ultrafast control of correlated electronic phases in van der Waals (vdW) heterostructures.

Raman optical activity (ROA), the dependence of Raman intensity on the circular polarization of incident and scattered light, has traditionally been observed in chiral molecules and magnetic materials, where inversion or time-reversal symmetry is broken. Here we demonstrate that ROA can also arise in a centrosymmetric and nonmagnetic ferroaxial crystal. Using circularly polarized Raman spectroscopy on single-crystalline ${\mathrm{NiTiO}}_3$, we observed a pronounced ROA signal in the cross-circular polarization configurations, which correlates with the ferroaxial domain structure. Our symmetry analysis, first-principles calculations of phonons, and tight-binding model calculations reveal that the natural ROA originates from the ferroaxial order and persists even within the electric dipole approximation. These results establish ROA as a powerful probe of ferroaxial order in centrosymmetric systems.

We study diffusion on multiplex networks with directed interlayer couplings. We demonstrate both numerically and analytically that even with undirected layers, interlayer directionality alone reproduces superdiffusion and the prime regime. We further reveal a new phenomenon, the directionality-induced jamming, whereby directed interlayer links hinder diffusion, fragmenting the system into dynamically disconnected components and preventing convergence to the steady state of the diffusion process. Via an optimization process, we show that this new regime is attainable in both toy models and real-world topologies. These findings underscore the crucial role of interlayer link directionality in shaping the emergent behavior of multiplex systems, with potential implications for the design and control of such systems.

Atomically thin transition metal dichalcogenide heterobilayers represent promising platforms for next-generation optoelectronic devices, wherein interlayer excitons serve as carriers for energy and information transport. At the atomic scale, quantum many-body interactions give rise to rich correlation states that challenge classical transport models. However, direct insights into how these correlation states govern exciton dynamics have been limited by the constraints of conventional electrical measurements. Here, we directly image ultrafast exciton diffusion in ${\mathrm{WS}}_2/{\mathrm{WSe}}_2$ moiré superlattices and uncover a tunable cascade transport mechanism governed by the interplay between Hubbard interactions and correlated electron states. By independently tuning exciton and carrier populations via optical injection and electrostatic doping, we demonstrate that strong on-site Hubbard interactions can significantly enhance exciton mobility. In contrast, correlated electron phases—such as generalized Wigner crystals—dramatically suppress transport through enhanced exciton-electron scattering. These findings provide a quantum-based strategy for controlling exciton transport, offering a versatile framework for designing reconfigurable excitonic circuits and multifunctional quantum optoelectronic devices.

The theory of the intrinsic nonlinear Hall effect, a key probe of quantum geometry, is plagued by conflicting expressions for the conductivity that is independent of the dissipation strength (rate, ${\mathrm{\Gamma }}^0$). We clarify the origin of this ambiguity by demonstrating that the “intrinsic” response is not universal, but is inextricably linked to how the dissipation mechanism shapes the nonequilibrium steady state (NESS) density matrix. We establish a benchmark by solving the exact NESS density matrix for a generic Bloch system coupled to a featureless fermionic bath. Our exact ${\mathrm{\Gamma }}^0$ conductivity decomposes into two parts: (i) a geometric contribution, ${\sigma }^{\mathrm{geo}}$, which establishes the definitive structure of the quantum metric contribution (including the intraband $\sim {\partial }_{k}g$ term), clarifying inconsistencies in the literature, and (ii) a novel, purely kinetic contribution, ${\sigma }^{\mathrm{kin}}\propto v^3{f}_0^{(4)}$, arising from mechanism-specific modifications to the occupation functions, which is absent in approaches that postulate, rather than derive, the relaxation dynamics. The discrepancies in both ${\sigma }^{\mathrm{geo}}$ and ${\sigma }^{\mathrm{kin}}$ between these distinct physical mechanisms prove that the ${\mathrm{\Gamma }}^0$ nonlinear conductivity is not a unique property of the Bloch Hamiltonian, but is contingent on the physical system-bath coupling.

We derive an inequality relating the finite-frequency linear response and fluctuations of an observable in a physical system in steady state. The relation holds for arbitrary observables and perturbations in general Markovian dynamics, including overdamped and underdamped Langevin systems and jump processes, both in and out of equilibrium. As a consequence, we obtain a universal upper bound on the broadband signal-to-noise ratio of noisy dynamics, which only depends on the damping constant and temperature. We further show that the inequality reduces to an equality for appropriately chosen observables or perturbations in linear systems, both overdamped and underdamped and both in and out of equilibrium.

Fractionally charged elementary excitations, the quasielectron and quasihole, are hallmarks of the fractional Chern insulator. We observe that spontaneous spin polarization in twisted ${\mathrm{MoTe}}_2$ leads to multiple species of low-energy quasiparticles distinguished by their spin quantum numbers. Through large-scale exact diagonalization calculations, we investigate the nature of these excitations and develop a method to extract their energetic properties. Focusing on $\theta =3.7°$ and filling factor $\nu =-2/3$ relevant to recent experiments, we show that spin-preserving (spinless) charge excitations have smaller gap than spin-flipping (spinful) excitations with and without band mixing. This result is in qualitative agreement with the measured magnetic field dependence of the transport gaps. Beyond spinless and spinful quasiparticle gaps, we extract the full quasielectron and quasihole “band structure” and find significant dispersion with emergent magnetic translation symmetry—a fundamental departure from the immobile excitations of the quantum Hall fluid. Our work establishes a framework for computing the properties of elementary excitations in fractional Chern insulators.

Storage and retrieval refer to the task of encoding an unknown quantum channel $\mathrm{\Lambda }$ into a quantum state, known as the program state, such that the channel can later be retrieved. There are two strategies for this task: classical and quantum strategies. The classical strategy uses multiple queries to $\mathrm{\Lambda }$ to estimate $\mathrm{\Lambda }$ and retrieves the channel based on the estimate represented in classical bits. The classical strategy turns out to offer the optimal performance for the storage and retrieval of unitary channels. In this work, we analyze the asymptotic performance of the classical and quantum strategies for the storage and retrieval of isometry channels. We show that the optimal fidelity for isometry estimation is given by $F=1-[d(D-d)/n]+O(n^{-2})$, where $d$ and $D$ denote the input and output dimensions of the isometry, and $n$ is the number of queries. This result indicates that, unlike in the case of unitary channels, the classical strategy is suboptimal for the storage and retrieval of isometry channels, which requires $n=\mathrm{\Theta }({\epsilon }^{-1})$ to achieve the diamond-norm error $\epsilon$. We propose a more efficient quantum strategy based on port-based teleportation, which stores the isometry channel in a program state using only $n=\mathrm{\Theta }(1/\sqrt{\epsilon })$ queries, achieving a quadratic improvement over the classical strategy. As an application, we extend our approach to general quantum channels, achieving improved program cost compared to prior results by Gschwendtner, Bluhm, and Winter [Quantum 5, 488 (2021)].

The solar system currently traverses the Local Interstellar Cloud (LIC), one of several warm cloudlets of the Complex of Local Interstellar Clouds (CLIC) in the solar neighborhood. The origin of these cloudlets is unknown and could be related to supernova shock wave dynamics. If supernovae are the source of these cloudlets or influence their properties, the CLIC may act as a cosmic archive for the supernova-produced radionuclide ${}^{60}\mathrm{Fe}$. We detected minuscule traces of interstellar ${}^{60}\mathrm{Fe}$ in 295 kg of the European Project for Ice Coring in Antarctica Dronning Maud Land ice core, covering the time period 40–81 kyr ago. We find an ${}^{60}\mathrm{Fe}/{}^{53}\mathrm{Mn}$ ratio of $(8\pm 5)\times {10}^{-4}$, slightly above the expected cosmogenic production, corresponding to an interstellar deposition rate of (${0.22}_{-0.12}^{+0.14}$) ${}^{60}\mathrm{Fe}$ $\mathrm{at}/{\mathrm{cm}}^2/\mathrm{yr}$. This influx is significantly lower than that observed in recent Antarctic snow and marine sediment records during the last 40 kyr. These results suggest that the LIC is a cosmic archive for supernova-produced ${}^{60}\mathrm{Fe}$. The imprinted ${}^{60}\mathrm{Fe}$ time profile is evidence for a changing local interstellar environment over the last 80 kyr.

Achieving invisibility in diffusive fields with metamaterials has long been hindered by a fundamental trade-off: suppressing external scattering by means of a metamaterial shell inevitably distorts the shell’s internal field, precluding perfect transparency. We overcome this limitation by introducing a dual-zero-scattering regime that simultaneously eliminates scattering in both the background medium and the metamaterial shell. Through a unified theoretical framework that integrates coordinate transformation with scattering cancellation, we demonstrate this concept both numerically and experimentally in thermal sensors, cloaks, and concentrators. The required shell’s anisotropic thermal conductivity is realized using deep-learning-optimized microstructures. This approach establishes a general paradigm for designing truly noninvasive devices in diffusion-based systems, with promising extensions to wave phenomena such as acoustics and electromagnetics.

A background-free intensity autocorrelation measurement for 10-keV femtosecond x-ray pulses is demonstrated using x-ray second harmonic generation. The narrow phase-matching condition of x-ray second harmonic generation allows for the selective generation of either the autocorrelation or background signals in a quasicollinear geometry with a crossing angle of $\sim 300\mathrm{\mu }\mathrm{rad}$, achieving a geometric time resolution of $\sim 1$ attosecond. The measured autocorrelation traces exhibit zero background and clearly reveal temporal modifications through an Si(311) monochromator, verifying x-ray temporal shaping with perfect crystals. The applicability of this method to attosecond x-ray pulses is also discussed.

Coulomb interactions deeply affect quantum transport in simple ballistic systems, but their impact on scaled up ballistic structures remains underexplored. Here, we theoretically consider a chain of small metallic dots with frozen charge dynamics connected by ballistic channels. We identify a neutral mode of transport that is specific to a chain with at least two islands and entwines local diffusion by neutral excitations with long-range correlations between the islands’ charge states. We show, as an experimentally measurable signature of this many-body behavior, that the Wiedemann-Franz law is violated with a Lorenz ratio scaling as the square root of the chain’s length.

The surprisingly rich physics of a single Coulomb-blockaded metallic island coupled to quantum Hall edge channels is now well established, giving rise to exotic quantum impurity states. Here, we show that qualitatively new physics emerges in arrays of such elements. Universal and robust behavior emerges for energy scales smaller than the charging energy of the islands. We consider a chain of $N$ metallic islands and find that it displays nonlocal responses. In particular, we demonstrate that for the bulk filling factor of $\nu =1$, the islands could support a finite heat flow without a temperature difference between them. Upon pinching the array with a quantum point contact, we predict an entropy change that scales with the number of islands as $\mathrm{\Delta }S=\frac{1}{2}{k}_B\log (N+1)$.

Topological solitons hold great promise for revolutionizing information and energy technologies, yet their controlled creation remains a major challenge. Here, we demonstrate room-temperature nucleation of fractional, skyrmion loops—three-dimensional, half-integer topological defects—within a nematic liquid crystal microfluidic cell. A single beam of linearly polarized light rotates the surface alignment, accumulating elastic twist until a topologically trivial texture collapses into a robust skyrmion loop. The loop’s cross section continuously morphs between half Néel skyrmions, antiskyrmions, and bimerons. Real-time polarized microscopy and Landau–de Gennes free energy based simulations reveal that the transition occurs via a $2\pi$ twist discontinuity and a sharp energy drop. The same protocol can be triggered by electric fields or local heating, and spawns a pair of $\pm 1$ topological monopoles that migrate along the loop to minimize the free energy. Our findings establish nematic liquid crystals as an optically rewritable, low-energy platform for generating arbitrary three-dimensional topological textures, offering immediate avenues for reconfigurable photonics and topological metamaterials.

In this Letter, we present a compelling and robust argument for the roles of neutrino fast flavor conversion (FFC) in the explosion mechanism of core-collapse supernova (CCSN), combining the multiangle FFC subgrid model rooted in quantum kinetic theory with the multidimensional four-species Boltzmann neutrino radiation hydrodynamics. Employing various progenitor masses and the nuclear equations of states, we find that the effect of FFC on CCSN explosion is bifurcated depending on the progenitors. For the lowest-mass progenitor, FFC facilitates the shock revival and enhances the explosion energy, whereas for higher-mass progenitors its impact is inhibitory. We identify the mass accretion rate as the key determinant governing this bifurcation. When the mass accretion rate is low (high), the contribution of FFC to neutrino heating becomes positive (negative) because the heating efficiency enhancement via FFC-driven spectral hardening of electron-type neutrinos dominates over (is outweighed by) the concurrent reduction in neutrino luminosity. Our results further highlight the limitations of approximate neutrino transport and demonstrate that a multiangle treatment is essential for accurately capturing FFC effects; otherwise, FFCs are missed and even generated spuriously.

Pancharatnam-Berry (PB) metasurfaces encode the geometric phase through the rotation of the meta-atom, which exhibits opposite phases and nearly equal conversion amplitudes in the two cross-polarized channels. This spin duality has long restricted PB metasurfaces to spin-symmetric responses with insufficient contrast for spin-selective operation. Here we experimentally demonstrate a regime in which the geometric phase is preserved while its spin duality is deliberately broken. By engineering the pillar-lattice symmetry mismatch together with the etch depth to maximize contrast, we decouple the conversion amplitudes of the two spin channels without affecting the geometric-phase evolution. This enables a spin-asymmetric geometric-phase response that has not been accessible in conventional PB designs. We verify the broken duality through far-field measurements that reveal the selective suppression of the conjugate channel normally enforced by the PB phase. These results establish an accessible pathway to geometric-phase metasurfaces operating beyond their long-standing spin-duality constraint, enabling new forms of spin-dependent wavefront control in optical communications and displays with flat-optical elements.

Energy loss of fast electrons in materials is a fundamental process in many fields spanning fusion research, high-energy-density physics, astrophysics, and material science. Contrary to conventional collisional theory that predicts greater energy loss in denser materials, we experimentally observe an anomalous phenomenon: high-current-density electron beams undergo significantly stronger deflection and stopping in low-average-density porous foams than in their denser counterparts. Pore-resolved simulations and theoretical analysis demonstrate that return currents along the foam’s skeleton generate multi-kilo-Tesla magnetic fields in the vacuum pores. These intense fields strongly scatter beam electrons, enhancing stopping by orders of magnitude beyond collisional predictions. The derived conditions for this anomalous stopping agree with experiments and simulations, establishing a new microstructure-mediated regime of beam-matter interaction with potential applications in charged-beam control for fusion and laboratory astrophysics.

Motility-induced phase separation (MIPS) is a central collective phenomenon in active matter, theoretically established in the overdamped regime. We discover that the dynamical origin of MIPS is fundamentally altered by inertia, which induces a cooling mechanism absent in overdamped active matter. This conclusion is supported by an active variant of the direct simulation Monte Carlo method and by a kinetic theory for inertial self-propelled hard spheres derived from the microscopic dynamics. In contrast to the overdamped case, both analyses demonstrate that inertial MIPS can occur even without impenetrability, as it originates from a density-dependent cooling mechanism due to the coupling of density, orientation, and temperature. This mechanism emerges from the competition between activity and a density-dependent collision rate arising from spatial correlations between colliding particles. These findings open a pathway to fundamentally connect inertial active matter with granular physics.