The missing mass of the ${}^{12}\mathrm{C}(p,d)$ reaction has been measured near the ${\eta }^{\prime }$-meson emission threshold in coincidence with a high-momentum proton to selectively collect ${\eta }^{\prime }\text{−}{}^{11}\mathrm{C}$ mesic nucleus formation events at GSI, Germany. A 2.5 GeV proton excites a carbon nucleus in order to form an ${\eta }^{\prime }$-mesic nucleus emitting a deuteron forward with an energy of $\sim 1.5\mathrm{GeV}$. The deuteron is momentum analyzed by the fragment separator used as a high-resolution spectrometer to deduce the excitation energy of the residual system. The large-acceptance detector WASA surrounding the target identifies high-momentum protons emitted in the decay of the ${\eta }^{\prime }$-mesic nucleus. The measured semiexclusive spectrum exhibits structures below the threshold though the statistical significance is limited. The spectrum is fitted by theoretically calculated spectra varying optical-potential parameters of the ${\eta }^{\prime }$-nucleus interaction. The analysis results indicate possible formation of ${\eta }^{\prime }$-mesic nuclei for the real potential depth of $\sim -61\mathrm{MeV}$ with a local statistical significance of $3.5\sigma$ and, taking into account the look-elsewhere effect, a global significance of $2.1\sigma$.

Ion acceleration in $Z$-pinch plasmas is traditionally linked to the axial direction of current. Here, we report the radial emission of MeV protons from a low-mass, hydrogen-containing $X$ pinch. Proton energies up to 3 MeV are observed in a hybrid $X$ pinch with a $30\mathrm{\mu }\mathrm{m}$ polyethylene fiber at a 400 kA peak current. The low-mass load, correlation of protons with hard x-rays, and timing of hard x-ray emission point to proton acceleration driven by current disruption following fiber disintegration. A new insight into the acceleration mechanism arises from the use of an interelectrode gap that is too short for magnetic fields to bend axially accelerated protons by $\pi /2$ radians; thus, the observed radial emission implies a substantial radial acceleration component. The radial emission also enables $X$-pinch-driven proton radiography, the exceptional potential of which is demonstrated with exploding wires.

Combining high-speed photography with direct force measurements, we investigate the impact dynamics of drops of cornstarch-water mixtures—a premier example of shear-thickening fluids—across a wide range of impact conditions. Our Letter identifies three distinct impact regimes. In addition to the liquidlike and solidlike behaviors generally expected for the impact-induced response of shear-thickening fluids, we uncover a counterintuitive regime in which high-concentration cornstarch-water mixtures display a liquidlike response at the onset of impact when shear rates are high and only transition to a solidlike behavior at later times as shear rates reduce. By integrating the classic drop-impact theory with the Reynolds-Darcy mechanism for dilatancy, we develop a unified model that quantitatively describes the impact dynamics of shear-thickening drops across all regimes. Our Letter reveals the unexpected response of shear-thickening fluids to ultrafast deformation and advances the fundamental understanding of drop impact for complex fluids.

We demonstrate high-resolution in situ imaging of density-wave ordering induced by cavity-mediated interactions in a unitary Fermi gas. We observe long-range spatial correlations throughout the formation of density waves, both for adiabatic preparation and following a quench, with a pattern controlled by the cavity mode structure. Our single-shot microscopic images together with the real-time readout of the cavity photons provide access to atom-photon correlations. We use this capability to investigate order fluctuations as a function of time following a quench and to directly confirm the correspondence between optical and atomic observables. Our system opens rich perspectives, from local patterning to correlation measurements in long-range interacting quantum gases.

Quantum interference phenomena in superconductors, such as Josephson interference and Little-Parks oscillations, serve as powerful probes of phase coherence, symmetry breaking, and vortex dynamics. However, they are typically observed in well-defined mesoscopic structures, and their behavior in the two-dimensional limit remains largely unexplored. Here, we report periodic magnetoresistance oscillations, superconducting interference patterns, and interfering diode effect in unpatterned few-layer ${\mathrm{NbSe}}_2$. These phenomena emerge exclusively within the superconducting fluctuation regime of thin samples, consistent with the enhanced anomalous metallic behavior of atomically thin ${\mathrm{NbSe}}_2$. The nonmonotonic temperature dependence of both the oscillation amplitude and the diode efficiency can be captured by a model in which thermally activated vortices traverse intrinsic supercurrent loops. Our results reveal that the observed interference phenomena originate from the lost of global phase coherence, providing a new route to accessing interference effects in unpatterned superconductors.

While equilibrium interfaces display universal large-scale statistics, interfaces in phase-separated active and driven systems are predicted to belong to distinct nonequilibrium universality classes. Yet, such behavior has proven difficult to observe, with most systems exhibiting equilibriumlike fluctuations despite their strongly nonequilibrium microscopic dynamics. We introduce a hard-disk model driven by active collisions, conceived as an effective two-dimensional description of a vibrofluidized granular system that, contrary to self-propelled models, displays clear nonequilibrium interfacial scaling. We observe for the first time, the $|\mathit{q}|\mathrm{KPZ}$ and wet-$|\mathit{q}|\mathrm{KPZ}$ universality classes while revealing a new, previously overlooked universality class arising in systems with slow solidlike or glassy dynamics. Conservation laws and slow dynamics select these distinct classes.

By leveraging nonlocal airborne acoustic metamaterials, we propose acoustic “ghost tunnels” that enable perfect tunneling while simultaneously functioning as an “empty” space for external waves incident upon their lateral boundaries. This remarkable property originates from two groups of eigenstates shifted along different directions in the momentum space: one exhibiting doubly degeneracy with directional linear dispersions, which is strictly protected by glide symmetries, and the other showing broad-angle impedance matching, characterized by arc-shaped equal-frequency contour. Upon selective excitation of such eigenstates through different boundaries, acoustic waves perceive the same metastructure, either as a perfect tunnel with strict bounds or as a reflectionless empty space. This exotic acoustic tunnel, verified through both simulations and experiments, establishes a versatile paradigm for novel acoustic manipulation.

Magnetoresistance studies of 2D systems are often shaped by the motion of electrons that occupy spatially confined wave functions, such as topological edge modes and disorder-induced bound states. Directly probing how such states form and behave in situ, under applied currents, provides a clear way of connecting microscopic physics to the macroscopic transport response. In this Letter, scanning tunneling potentiometry is used to probe the local, current-induced electrochemical potential of carriers in graphene near circular $p\text{−}n$ junctions in an out-of-plane magnetic field ranging from 0 to 1.4 T. These measurements provide detailed information about the motion of carriers at the nanometer scale, revealing how it evolves with increasing field. The electrochemical potential displays distinct patterns, such as dipoles, spirals, and concentric disks in weak, moderate, and high fields, respectively. The size and orientation of these patterns can be used to understand how local carrier dynamics change in different transport regimes as well as to directly extract physical parameters such as the electron mean free path and cyclotron diameter.

Bistability—two distinct stable states under identical parameters—is not only a fundamental physical concept but also of importance in practical applications. While plasmon-polaritonic bistability representing history-dependent stable states within plasmonic systems has been theoretically predicted, it has yet to be demonstrated experimentally due to challenges in realizing suitable nonlinearity at feasible electric-field strengths. Here, we report the experimental observation of electrically driven plasmon-polaritonic bistability in graphene/hexagonal-boron-nitride/graphene tunneling transistors, achieved through momentum-conserving resonant tunneling of Dirac electrons. Using a small twist angle between graphene layers, we engineered devices exhibiting both electronic and plasmon-polaritonic bistability. This bistable plasmonic behavior can be precisely tuned through load resistance and electrostatic gating. Our findings open new pathways for exploring nonlinear optical and electronic phenomena in van der Waals heterostructures and mark a significant advance in nanoplasmonics, with potential applications in optical memory, sensing, and optoelectronic switching.

We demonstrate a blue-detuned magneto-optical trap (MOT) of a polyatomic molecule, calcium monohydroxide (CaOH). We identify a novel MOT frequency configuration that produces high spatial compression of the molecular cloud. This high compression MOT achieves a cloud radius of $59(5)\mathrm{\mu }\mathrm{m}$ and a peak density of $8(2)\times {10}^8{\mathrm{cm}}^{-3}$. We experimentally compare several blue-detuned MOT schemes for CaOH and find good agreement between our data and Monte Carlo simulations.

Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in space and laboratory plasmas. The nonlinear behavior of these modes is thought to play a key role in important problems in space plasma, such as the heating of the solar corona and solar wind turbulence. In particular, theoretical predictions show that these Alfvén waves may be unstable to various parametric instabilities, but space observations of these processes are limited. We demonstrate the first measurement of the Alfvén wave parametric decay instability (PDI) growth rate. Experiments are conducted on the Large Plasma Device at UCLA in which a high amplitude $\delta B/B_0\sim 0.7\%$ pump Alfvén wave is launched from one end of the device and a smaller seed Alfvén wave is launched from the other side. When the frequency of the seed wave is chosen to match the backward wave expected from PDI, damping of the seed wave is reduced. We compare this reduction in damping to the theoretically expected PDI growth rate while accounting for acoustic mode damping. Results show agreement between measurements and theoretical predictions. This not only provides critical validation for PDI theories and simulations that could help interpret future space observations but also suggests a new way of studying similar nonlinear wave phenomena.

Photonic crystals are artificial structures with periodic geometries that manipulate light at the wavelength scale. Recently, they have garnered significant attention in the field of topological photonics, where advanced band manipulation is explored to achieve breakthroughs in topological device applications. Conventional photonic crystals predominantly rely on a single spatial domain, characterized by spatially distributed dielectric modulation or metallic resonance. However, the degrees of freedom offered by spatial domains are often overlooked. Here, we theoretically propose and experimentally demonstrate photonic metacrystals that manipulate electromagnetic waves via minimal surfaces in three-dimensional space. These minimal surfaces partition the three-dimensional space into two complementary yet dual subspaces, each supporting a chiral topological semimetal. This spatial duality induces double-band degeneracy, analogous to the well-known time-reversal Kramers degeneracy, which has long been sought in classical systems. Previous proposals either relied on unrealizable strict symmetries or achieved double degeneracy only along high-symmetry lines. In contrast, we demonstrate that our double degeneracy exists globally, akin to the intrinsic spin degree of freedom of electrons. Furthermore, we extend the zero-frequency sixfold degeneracy of Maxwell’s equations to a nonzero frequency range, which significantly facilitates the characterization of the intrinsic topological properties. Our study provides new insights into the geometric foundations of topological physics.

Multiferroics, which combine ferroelectric and magnetic order, offer a transformative platform for next-generation electronic devices. However, the intrinsic competition between the mechanisms driving ferroelectricity and magnetism in single-phase materials severely limits their performance, typically resulting in weak magnetoelectric coupling at room temperature. Here, we propose a solution to this long-standing challenge through the novel concept of fractional quantum multiferroics (FQMF), where strong magnetoelectric coupling is naturally realized by coupling fractional quantum ferroelectricity with altermagnetism. Symmetry analysis shows that reversing the fractional quantum ferroelectricity polarization necessarily inverts the altermagnetic spin splitting under parity-time or time-reversal operations. A minimal tight-binding model reproduces this effect, demonstrating electrically driven spin control without rotating the Néel vector. First-principles calculations further identify a broad family of candidate materials in two and three dimensions, including bulk MnTe, ${\mathrm{Cr}}_2{\mathrm{S}}_3$, ${\mathrm{Mn}}_4{\mathrm{Bi}}_3{\mathrm{NO}}_{15}$ and two-dimensional ${\mathrm{AB}}_2$ bilayers such as ${\mathrm{MnX}}_2$ ($\mathrm{X}=\mathrm{Cl}$, Br, I), ${\mathrm{CoCl}}_2$, ${\mathrm{CoBr}}_2$, and ${\mathrm{FeI}}_2$. Notably, MnTe exhibits a high Néel temperature ($\sim 300\mathrm{K}$) and a large electrically switchable spin splitting ($\sim 0.8\mathrm{eV}$), demonstrating room-temperature magnetoelectric performance that surpasses that of conventional multiferroics. To further showcase the technological potential, we propose an electric-field-controlled FQMF tunnel junction based on MnTe that achieves tunneling magnetoresistance exceeding 300%. This Letter establishes FQMF as a distinct and promising route to achieving room-temperature robust electrically controlled magnetism, opening a new avenue for voltage-controlled spintronics.

We experimentally investigate the superfluid properties of a two-dimensional, weakly interacting Bose-Einstein condensate in the zero-temperature regime when it is subjected to a triangular optical lattice potential. We implement an original method, which involves solving the hydrodynamic continuity equation to extract the superfluid fraction tensor from the measured in situ density distribution of the fluid at rest. In parallel, we apply an independent dynamical approach that combines compressibility and sound velocity measurements to determine the superfluid fraction. Both methods yield consistent results in good agreement with simulations of the Gross-Pitaevskii equation as well as with the Leggett bounds determined from the measured density profiles.

Y-kapellasite [${\mathrm{Y}}_3{\mathrm{Cu}}_9{(\mathrm{OH})}_{19}{\mathrm{Cl}}_8$], which hosts an original anisotropic kagome sublattice, is a promising candidate for studying elusive and complex correlated physics. It exhibits a theoretically predicted in-plane $(1/3,1/3)$ magnetic order [Hering et al., npj Comput. Mater. 8, 1 (2022)], but its magnetic interaction values place it close to a phase boundary to a spin liquid state [Chatterjee et al., Phys. Rev. B 107, 125156 (2023)]. Our $\mathrm{\mu }\mathrm{SR}$ measurements under hydrostatic pressure demonstrate the complete suppression of static magnetism in favor of a fully dynamical ground state at 2.3 GPa. Complementary high-pressure x-ray and optical phonon measurements reveal a gradual reduction of the kagome anisotropy, enhancing magnetic frustration without structural transitions. Our results establish Y-kapellasite as a rare clean kagome model in which long-range order is suppressed by pressure-tuned frustration, the first fingerprint for the realization of a quantum spin liquid without strong disorder.

Dense bacterial suspensions at fluid interfaces provide a natural platform to explore active turbulence in a dimensional mismatch: active units are restricted to a two-dimensional surface, while the induced flows extend into the surrounding three-dimensional liquid. Using hydrophobic Serratia marcescens at the air-water interface, we realize interfacial bacterial turbulence as a distinct class of active turbulence. The system exhibits compressible in-plane flows, with the vortex size increasing with the thickness of the underlying fluid before saturating at a finite scale. This behavior contrasts sharply with bulk active turbulence, where correlation length typically scales with system size. Hydrodynamic theory, together with direct measurements of the three-dimensional flow field, shows that the coupling between interfacial and bulk flows sets the emergent length scale. Our results uncover the fundamental physics of interfacial bacterial turbulence and open new strategies for geometric control of collective active flows.

We report a measurement of the cosmic ray helium energy spectrum in the energy interval 0.16–13 PeV, derived by subtracting the proton spectrum from the light component (proton and helium) spectrum obtained with observations made by the Large High Altitude Air Shower Observatory (LHAASO) under a consistent energy scale. The helium spectrum shows a significant hardening centered at $E\simeq 1.1\mathrm{PeV}$, followed by a softening at $\sim 7\mathrm{PeV}$, indicating the appearance of a helium “knee.” Comparing the proton and helium spectra in the LHAASO energy range reveals some remarkable facts. In the lower part of this range, in contrast to the behavior at lower energies, the helium spectrum is significantly softer than the proton spectrum. This results in protons overtaking helium nuclei and becoming the largest cosmic ray component at $E\simeq 0.7\mathrm{PeV}$. A second crossing of the two spectra is observed at $E\simeq 5\mathrm{PeV}$, above the proton knee, when helium nuclei overtake protons to become the largest cosmic ray component again. These results have important implications for our understanding of the Galactic cosmic ray sources.

We report improved measurements of the all flavor astrophysical neutrino spectrum with IceCube by combining complementary neutrino samples in two independent analyses. Both analyses show evidence of a harder spectrum at energies below $\sim 30\mathrm{TeV}$ compared to higher energies where the spectrum is well characterized by a power law. The spectrum is better described by a log parabola or a broken power law, the latter being the preferred model. Both, however, reject a single power law over an energy range 5 TeV–10 PeV with a significance $>4\sigma$, providing new constraints on properties of cosmic neutrino sources.

Recent studies have drawn growing attention on nonrelativistic odd-parity magnetism in the wake of altermagnets. Nevertheless, odd-parity spin splitting is often believed to appear in noncollinear magnetic configurations. Here, using symmetry arguments and effective model analysis, we show that Floquet engineering offers a universal strategy for achieving odd-parity magnetism in two-dimensional (2D) collinear antiferromagnetism under irradiation of periodic driving light fields such as circularly polarized light, elliptically polarized light, and bicircular light. The symmetry requirements and three distinct lattice models of potential candidates are established. Strikingly, the light-induced odd-parity spin splitting can be flexibly controlled by adjusting the crystalline symmetry or the polarization state of incident light, enabling the reversal or conversion of spin splitting. By combining first-principles calculations and Floquet theorem, we present illustrative examples of 2D collinear antiferromagnetic (AFM) materials to verify the light-induced odd-parity magnetism. Our Letter not only offers a powerful approach for uniquely achieving odd-parity spin splitting with high tunability, but also expands the potential of Floquet engineering in designing unconventional compensated magnetism.

Altermagnets, recently discovered unconventional magnets distinct from both ferro- and antiferromagnets, have rapidly emerged as a prominent research topic in condensed matter physics. Altermagnets are characterized by alternating collinear magnetic moments with zero net magnetization in real space, and spin splittings with even-parity symmetry in momentum space. However, their counterparts exhibiting odd-parity spin splittings are generally thought to be absent in collinear magnets. Here, we show that such unconventional odd-parity magnets can be induced from collinear antiferromagnets by symmetry engineering. Remarkably, using effective model analysis within a Floquet-theory framework, we demonstrate that circularly polarized light irradiation of conventional antiferromagnetic lattices breaks a spin-preserving pseudo-time-reversal symmetry and induces both $p$- and $f$-wave magnets, realizing novel magnetic states dubbed “Floquet odd-parity collinear magnets.” Moreover, we also uncover light-induced antiferromagnetic Chern insulating states in the $f$-wave magnets. The proposed Floquet odd-parity magnet is confirmed by first-principles calculations of ${\mathrm{MnPSe}}_3$ under circularly polarized light. Our Letter not only proposes a new class of unconventional magnets, but also opens an avenue for light-induced magnetic phenomena in spintronic applications.