We report the first direct observation using a retarding potential analyzer of time-resolved ion energy distribution functions (IDFs) in a Hall thruster (HT) on two distinct time scales corresponding to the breathing mode ($\sim \mathrm{kHz}$) and the ion transit time oscillation (ITTO, $\sim 100\mathrm{kHz}$). We combined the dynamic time warping technique with a calculation of the cumulative quadratic distance applied to measure weakly nonperiodic oscillations to achieve a previously inaccessible fine resolution of ion-acceleration dynamics driven by ITTOs and revealing the footprint of multiple ion bunches on the IDF in accordance with theory. The analysis demonstrates the significant role of high-frequency instabilities in shaping the IDF and explains fundamental mechanisms of axial wave-particle interactions and ion transport in HTs.

We show that the honeycomb tight-binding model hosts an exact microscopic avatar of its low-energy SU(2) valley symmetry and parity anomaly. Specifically, the SU(2) valley symmetry arises from a collection of conserved, integer-quantized charge operators that obey the Onsager algebra. Along with lattice reflection and time-reversal symmetries, this Onsager symmetry has a Lieb-Schultz-Mattis (LSM) anomaly that matches the parity anomaly in the IR. Indeed, we show that any local Hamiltonian commuting with these symmetries cannot have a trivial unique gapped ground state. We study the phase diagram of the simplest symmetric model and survey various deformations, including Haldane’s mass term, which preserves only the Onsager symmetry. Our results place the parity anomaly in $2+1\mathrm{D}$ alongside Schwinger’s anomaly in $1+1\mathrm{D}$ and Witten’s SU(2) anomaly in $3+1\mathrm{D}$ as ’t Hooft anomalies that can arise from the Onsager symmetry on the lattice.

Ferroelectric metals, traditionally considered mutually exclusive, face enduring challenges owing to screening effects of itinerant electrons on ferroelectric order. However, in certain van der Waals (vdW) heterostructures, two-dimensional materials with distinct structural and physical properties can be alternatingly arranged in layers, retaining their individual characteristics and thereby enabling the coexistence of ferroelectricity and metallicity. Here, we report the coexistence of robust in-plane ferroelectricity and exceptional metallicity in a natural vdW superlattice ${(\text{SnSe})}_{1.16}({\text{NbSe}}_2)$ crystal, exhibiting high-density carriers ($>{10}^{21}{\mathrm{cm}}^{-3}$), superconductivity ($T_c\sim 3.25\mathrm{K}$), and Curie temperature up to 383 K. The weak-coupling electronic and phononic natures stabilize in-plane ferroelectricity against screening by high-density carriers, confirming the decoupled electron mechanism. Moreover, we demonstrate the first ferroelectric memristor, where the metallic channel conductance is manipulated through polarization dynamics. Our Letter establishes a universal platform for designing multi-order parameters quantum-confined materials, and opens new avenues for energy-efficient functional electronics.

We report limits on weakly interacting massive particle (WIMP) dark matter derived from three years of data collected by the COSINE-100 experiment with NaI(Tl) crystals, achieving an improved energy threshold of 0.7 keV. This lowered threshold enhances sensitivity in the sub-GeV mass range, extending the reach for direct detection of low-mass dark matter. Although no excess of WIMP-like events was observed, the increased sensitivity enabled a model-insensitive comparison between the expected WIMP signal rate—based on mass limits from our data—and DAMA’s reported modulation amplitude. Our findings strongly disfavor the DAMA signal as originating from WIMP interactions, fully excluding DAMA/LIBRA $3\sigma$ allowed regions and providing enhanced WIMP mass limits by an order of magnitude in the spin-independent model compared to previous results. In the spin-dependent model, cross-section upper limits were obtained in the mass range [0.1–5.0] $\mathrm{GeV}/{\mathrm{c}}^2$, with additional sensitivity to sub-GeV WIMPs through the inclusion of the Migdal effect. These results represent substantial progress in low-mass dark matter exploration and reinforce constraints on the longstanding DAMA claim.

Collective neutrino flavor conversions in core-collapse supernovae begin with instabilities, initially triggered when the dominant ${\nu }_e$ outflow concurs with a small antineutrino flux of opposite lepton number, with ${\overline{\nu }}_e$ dominating over ${\overline{\nu }}_{\mu }$. When these “flipped” neutrinos emerge in the energy-integrated angular distribution (angular crossing), they initiate a fast instability. However, before such conditions arise, spectral crossings typically appear within 20 ms of collapse, i.e., local spectral excesses of ${\overline{\nu }}_e$ over ${\overline{\nu }}_{\mu }$ along some direction. Therefore, postprocessing supernova simulations cannot consistently capture later fast instabilities because the early slow ones have already altered the conditions.

Neutron stars (NSs) with their strong magnetic fields and hot dense cores could be powerful probes of axions, a classic benchmark of feebly coupled new particles, through abundant production of axions with the axion-nucleon coupling and subsequent conversion into x-rays due to the axion-photon coupling. In this Letter, we point out that the pulsation structures in both the intensity and polarization of x-rays from NSs could provide us additional information about axions and their couplings. We develop new analytical formalisms of pulsation-polarization structure applicable to a wide range of NSs in the axion scenario and argue that they hold in complicated astrophysical environments. As a case study, we apply our formalism to a representative X-ray Dim Isolated Neutron Star, RX J1856.6-3754, with an unexpected hard x-ray excess which might be axion induced. We show with an updated fit that the axion explanation is compatible with both the intensity and pulsation data available, and combining the pulsation data does not shift the posterior by more than $1\sigma$. Yet, the preferred parameter space is close to being excluded by other astrophysical constraints. With a 75% reduction of the uncertainties in the pulsation data, we could potentially draw a definite conclusion on the axion-induced x-rays at more than $3\sigma$ level.

We present the first lattice QCD determination of the $\mathrm{\Lambda }\to N$ vector and axial-vector form factors, which are essential inputs for studying the semileptonic decay $\mathrm{\Lambda }\to p\ell {\overline{\nu }}_{\ell }$. This channel provides a clean, theoretically controlled avenue for extracting the Cabibbo-Kobayashi-Maskawa matrix element $|V_{us}|$ from the baryon sector. Our analysis uses a gauge ensemble with physical light, strange, and charm quark masses and yields the most precise determination to date of the full set of transition form factors—including second-class contributions—as well as the associated couplings, radii, and the ratio of muon-to-electron decay rates, an observable sensitive to possible nonstandard scalar and tensor interactions. We compare our nonperturbative results with next-to-next-to-leading order expansions in the small parameter $\delta =(m_{\mathrm{\Lambda }}-m_N)/m_{\mathrm{\Lambda }}\approx 0.16$. We find that the common phenomenological approximation of neglecting the $q^2$ dependence of the form factors leads to a $\sim 4\%$ deviation in the decay rate. This underscores the critical importance of precise, fully nonperturbative form factor inputs for achieving the subpercent precision targets of upcoming experimental programs.

The half-lives of 24 isotopes ranging from sulfur to potassium were measured using the ZeroDegree Advanced Decay Station at the Radioactive Isotope Beam Factory, including six of the most neutron-rich—${}^{47}\mathrm{S}$, ${}^{48,49}\mathrm{Cl}$, ${}^{51,52}\mathrm{Ar}$, ${}^{55}\mathrm{K}$—for the first time, while the precision for ${}^{48}\mathrm{Ar}$ and ${}^{53,54}\mathrm{K}$ was significantly improved. Two prominent features are found: First, a half-life drop at ${}^{54}{\mathrm{K}}_{35}$ relative to ${}^{52,53}\mathrm{K}$, supporting the persistence of the $N=34$ subshell closure in potassium with $Z=19$. Second, a high $\beta$-decay rate for ${{}^{48}\mathrm{Cl}}_{31}$ compared to ${}^{47}\mathrm{Cl}$ and ${}^{49}\mathrm{Cl}$, which can be explained by the critical role of the $\nu 1p_{1/2}$ orbital in shell-model calculations. The present calculations indicate that the $N=32$ subshell gap in chlorine with $Z=17$ is slightly smaller than that in calcium ($Z=20$), and the significant excitation across the $N=32$ subshell in ${{}^{48}\mathrm{Cl}}_{31}$ is mainly due to strong configuration mixing.

A long-standing discrepancy between measured and predicted beam-normal single-spin asymmetries $A_n$ in elastic electron scattering off ${}^{208}\mathrm{Pb}$ has challenged our understanding of two-photon exchange (TPE) in heavy nuclei. We report a new measurement at 570 MeV and $Q^2=0.04{\mathrm{GeV}}^2/c^2$, yielding $A_n=[-9.1\pm 2.1(\mathrm{stat})\pm 0.7(\mathrm{syst})]\mathrm{ppm}$. This nonzero value contrasts with previous results at higher energies and suggests a kinematic dependence of TPE effects not captured by current theory, prompting a reevaluation of earlier interpretations.

The solar composition problem has puzzled astrophysicists for more than 20 years. Recent measurements of carbon-nitrogen-oxygen (CNO) neutrinos by the Borexino experiment show a $\sim 2\sigma$ tension with the “low-metallicity” determinations. ${}^{14}\mathrm{N}(p,\gamma {)}^{15}\mathrm{O}$, the slowest reaction in the CNO cycle, plays a crucial role in the standard solar model (SSM) calculations of CNO neutrino fluxes. Here we report a direct measurement of the ${}^{14}\mathrm{N}(p,\gamma {)}^{15}\mathrm{O}$ reaction, in which $S$-factors for all transitions were simultaneously determined in the energy range of $E_{\mathrm{p}}=110–260\mathrm{keV}$ for the first time. Our results resolve previous discrepancies in the ground-state transition, yielding a zero-energy $S$-factor $S_{114}(0)=1.93\pm 0.10\mathrm{keV}\mathrm{b}$, which is 15% higher than the $1.68\pm 0.14\mathrm{keV}\mathrm{b}$ recommended in Solar Fusion III (SF-III). With our $S_{114}$ values, the SSM B23-MB22p, and the latest global analysis of solar neutrino measurements, the C and N photospheric abundance determined by the Borexino experiment is updated to $N_{\mathrm{CN}}=(4.42_{-0.63}^{+0.70})\times {10}^{-4}$. This new $N_{\mathrm{CN}}$ value agrees well with latest “high-metallicity” composition; however, it is also consistent with the “low-metallicity” determination within $\sim 1\sigma$ CL, indicating that the solar metallicity problem remains an open question. In addition, the significant reduction in the uncertainty of $S_{114}$ paves the way for the precise determination of the CN abundance in future large-volume solar neutrino measurements.

We investigate the pressure evolution of charge density wave (CDW) order in the intermetallic compound ${\mathrm{BaFe}}_2{\mathrm{Al}}_9$, which undergoes a pronounced first-order CDW transition $\sim 112\mathrm{K}$ at ambient pressure. High-pressure electrical resistivity and magnetization measurements reveal a systematic enhancement of the CDW transition temperature ($T_{\mathrm{CDW}}$) at a rate of $\sim 60\mathrm{K}/\mathrm{GPa}$, reaching 300 K under $\sim 3.2\mathrm{GPa}$. The transition sharpness diminishes with pressure, indicating a crossover from first- to second-order behavior. Fermi liquid (FL) fits to the low-temperature resistivity reveal an increase in residual resistivity and a nonmonotonic evolution of the FL coefficient, indicating a pressure-induced Fermi surface (FS) reconstruction. Synchrotron x-ray diffraction reveals anisotropic lattice compression, a change in the compression trend of lattice parameters, and an abrupt change in microstrain at $\sim 3.6\mathrm{GPa}$. Density functional theory calculations reveal pressure-induced flattening of quasi-two-dimensional FS sheets associated with the CDW nesting vector, consistent with enhanced nesting. These findings highlight the critical role of lattice strain and electronic structure evolution in stabilizing a high-temperature CDW phase, making ${\mathrm{BaFe}}_2{\mathrm{Al}}_9$ a rare example of a three-dimensional material where pressure promotes rather than suppresses the CDW order.

Recent advances in multigap topological phases—characterized by invariants like Euler and second Stiefel-Whitney classes across multiband subspaces—highlight their dependence on non-Abelian braiding of momentum-space band degeneracies in adjacent gaps. Here, we theoretically predict and experimentally demonstrate that two of such topological phases can coexist within a single system using vectorial elastic waves. The inherent coupling between different polarization modes enables non-Abelian braiding of nodal points of multiple energy band gaps and results in hybrid Euler and Stiefel-Whitney topological insulator phases. We furthermore unveil the central role played by the topologically stable Goldstone modes’ degeneracy. Our findings represent the first realization of hybrid phases in vectorial fields exhibiting topologically nontrivial Goldstone modes, paving the way for bifunctional applications that leverage the hybrid topological edge and corner states.

Recent research on sliding ferroelectricity in various two-dimensional bilayers and multilayers has shown its promising application potential and emerging new physics distinct from conventional ferroelectricity. However, it stems from van der Waals interactions of asymmetrically stacked layers, so the polarizations are weak. Here, we propose that in most layered ion conductors, the asymmetric stacking of layers will give rise to a unique type of ionic sliding ferroelectricity. The major weakness is overcome since the vertical polarizations are generally enhanced by an order of magnitude, which is reversible via in-plane translation of layers and ions. Strikingly, the switching of vertical polarization is intercorrelated to various combinations of in-plane layer sliding and ion displacement modes, which may lead to quantized or fractional quantum ferroelectric switching. We also show first-principles evidence for the wide existence of ionic sliding multiferroicity with altermagnetism as well as ferroelectric control of large altermagnetic spin splitting.

Active systems comprise a class of nonequilibrium dynamics in which individual components autonomously dissipate energy. Efforts towards understanding the role played by activity have centered on computation of the entropy production rate (EPR), which quantifies the breakdown of time reversal symmetry. A fundamental difficulty in this program is that high dimensionality of the phase space renders traditional computational techniques infeasible for estimating the EPR. Here, we overcome this challenge with a novel deep learning approach that estimates probability currents directly from stochastic system trajectories. We derive a new physical connection between the probability current and two local definitions of the EPR for inertial systems, which we apply to characterize the departure from equilibrium in a canonical model of flocking. Our results highlight that entropy is produced and consumed on the spatial interface of a flock as the interplay between alignment and fluctuation dynamically creates and annihilates order. By enabling the direct visualization of when and where a given system is out of equilibrium, we anticipate that our methodology will advance the understanding of a broad class of complex nonequilibrium dynamics.

We present a geometric framework for Hamiltonian quantum time crystals, emphasizing the pivotal role of continuous symmetries and their associated conserved charges. In this approach, a time crystal is identified as a minimum-energy ground state that is parallel transported along a family of Fock spaces, with time evolution realized as a symmetry transformation. This parallel transport is implemented via a generalized, time-dependent Bogoliubov transformation, ensuring coherence across the Fock spaces. Revisiting Goldstone’s original analysis, we show that in the presence of a time crystal, the Goldstone mode acquires a mass and its direction oscillates periodically in Higgs space. Our formulation circumvents existing no-go theorems that would otherwise forbid quantum time-crystalline order. We place time crystals within the broader context of quantum many-body physics and field theory, drawing analogies to superconductivity and quantum field theory in time-dependent backgrounds.

Driven-dissipative many-body systems support nontrivial quantum phases absent in equilibrium. As a prominent example, the interplay between coherent driving and collective dissipation can lead to a dynamical quantum phase that spontaneously breaks time-translation symmetry. This so-called boundary time crystal (BTC) is fragile in the presence of local dissipation, which can easily relax the system to a stationary state. In this Letter, we demonstrate a robust BTC that is intrinsically induced by local dissipation. We provide extensive numerical evidence to support the existence of the BTC and study its behaviors in different regimes. In particular, with decreasing interaction range, we identify a transition from mean-field limit cycles to correlated BTCs featuring sizable quantum correlations. Our studies significantly broaden the scope of nonequilibrium phases and shed new light on the experimental search for dynamical quantum matter.