We investigate the nonlinear coupling between acoustic (ac) and optical (op) modes in the coupled magnetization dynamics of synthetic antiferromagnets, utilizing current-driven resonance spectroscopy. A clear spectral splitting is evident in the ac mode when strongly excited by the radio frequency current at a driving frequency half that of the op mode resonance. The Landau-Lifshitz phenomenology aligns with the experimental observations, affirming the coupling of the radio-frequency-excited ac and op modes through three-magnon mixing. The nonlinearity enables a Rabi-like splitting in an in-plane magnetized synthetic antiferromagnet without breaking its natural symmetries. This discovery holds potential for advancing our understanding of nonlinear antiferromagnetic dynamics.

While dual-phase xenon time projection chambers have driven the sensitivity toward weakly interacting massive particles at the $\mathrm{GeV}/c^2$ to $\mathrm{TeV}/c^2$ mass scale, the scope for sub-$\mathrm{GeV}/c^2$ dark matter particles is hindered by a limited nuclear recoil energy detection threshold. One approach to probe for lighter candidates is to consider cases where they have been boosted by collisions with cosmic rays in the Milky Way, such that the additional kinetic energy lifts their induced signatures above the nominal threshold. In this Letter, we report first results of a search for cosmic ray-boosted dark matter (CRDM) with a combined $4.2\mathrm{metric}\mathrm{ton}/\mathrm{yr}$ exposure from the LUX-ZEPLIN experiment. We observe no excess above the expected backgrounds and establish world-leading constraints on the spin-independent CRDM-nucleon cross section as small as $3.9\times {10}^{-33}{\mathrm{cm}}^2$ at 90% confidence level for sub-$\mathrm{GeV}/c^2$ masses.

Interfacial interactions often promote the emergence of unusual phenomena in two-dimensional systems, including high-temperature superconductivity. Here, we report the observation of full-gap superconductivity with a maximal spectroscopic temperature up to 26 K in a BaAs monolayer grown on ferropnictide $\mathrm{Ba}({\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{As}}_2$ (abbreviated as BFCA) epitaxial films. The superconducting gap remains robust even when the thickness of underlying BFCA is reduced to the monolayer limit, in contrast to the rapid suppression of $T_{\mathrm{c}}$ in standalone BFCA thin films. We reveal that the exceptional crystallinity of the $\mathrm{BaAs}/\mathrm{BFCA}$ heterostructures, featured by their remarkable electronic and geometric uniformities, is crucial for the emergent full-gap superconductivity with mean-field temperature dependence and pronounced bound states within magnetic vortices. Our findings open up new avenues to unravel the mysteries of unconventional superconductivity in ferropnictides and advance the development of FeAs-based heterostructures.

Smart active matter has the ability to control its motion guided by individual policies to achieve collective goals. We introduce a theoretical framework to study a decentralized learning process in which agents can locally exchange policies to adapt their behavior and maximize a predefined reward function. We use our formalism to derive explicit hydrodynamic equations for the policy dynamics. We apply the theory to two different microscopic models where policies correspond either to fixed parameters similar to evolutionary dynamics or to state-dependent controllers known from the field of robotics. We find good agreement between theoretical predictions and agent-based simulations. By deriving fundamental control parameters and uncertainty relations, our work lays the foundations for a statistical physics analysis of decentralized learning.

A highly charged muonic ion is a unique few-body atomic system where a negatively charged muon and a few electrons are simultaneously bound to a single nucleus. We report the first state-selective observation of highly charged muonic Ar ($\mu \mathrm{Ar}$) by electronic $K$ x-ray spectroscopy using an array of transition-edge sensor microcalorimeters. The high-precision $K$ x-ray spectra provide a clear signature of the presence of muonic atoms with one, two, and three electrons, i.e., H-like, He-like, and Li-like $\mu \mathrm{Ar}$. With the aid of theoretical calculations, we confirmed that the peak positions are consistent with the x-ray energies from highly charged Cl ions, and the intensities reflect deexcitation dynamics of highly charged $\mu \mathrm{Ar}$.

Acceleration of positive muons from thermal energy to 100 keV has been demonstrated. Thermal muons were generated by resonant multiphoton ionization of muonium atoms emitted from a sheet of laser-ablated aerogel. The thermal muons were first electrostatically accelerated to 5.7 keV, followed by further acceleration to 100 keV using a radio-frequency quadrupole with an intensity of $2\times {10}^{-3}{\mu }^{+}/\mathrm{pulse}$. The transverse normalized rms emittance of the accelerated muons in the horizontal and vertical planes were $0.85\pm 0.25(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}{)}_{-0.13}^{+0.22}(\mathrm{syst})\pi \mathrm{mm}\mathrm{mrad}$ and $0.32\pm 0.03{(\mathrm{stat})}_{-0.02}^{+0.05}(\mathrm{syst})\pi \mathrm{mm}\mathrm{mrad}$, respectively. The measured emittance values demonstrated phase-space reduction by a factor of $2.0\times {10}^2$ (horizontal) and $4.1\times {10}^2$ (vertical) allowing good acceleration efficiency. These results pave the way to realize the first-ever muon accelerator for a variety of applications in particle physics, material science, and other fields.

We investigate the formation and dynamics of Jones-Roberts solitons in a smoothly inhomogeneous quantum fluid. To do so, we create a superfluid of light using a paraxial, near-resonant laser beam propagating through a hot rubidium vapor. We excite a bounded vortex-antivortex dipole in the superfluid and observe its transition to a rarefaction pulse and back, in agreement with the seminal predictions of Jones and Roberts. Employing an analogy with ray optics, we calculate the trajectory of the interacting vortices, deriving an effective refractive index from the inhomogeneous fluid density. Finally, we examine analytically and experimentally the superfluid velocity correlations, observing a transfer of coherence from incompressible to compressible velocity of the quantum fluid, a direct signature of the dynamical conversion between vortices and the rarefaction pulse.

Spin-triplet pairing of superconductivity, drawing huge attention by enabling future technologies in quantum computing, spintronics, and other fields, can host unique transport phenomena. Here, we report gigantically enhanced nonreciprocal transport in the superconducting fluctuation regime of ${\mathrm{KTaO}}_3$-based interface superconductors. Notably, the observed nonreciprocity undergoes a sign reversal compared to the normal state. Combining experimental observations with theoretical modeling, we identify its dominant mechanism as the vortex motion and parity mixing of spin-singlet and spin-triplet pairings. We also provide evidence for an attractive spin-triplet pairing interaction. Furthermore, the nonreciprocal response is highly tunable by orders of magnitude using electrostatic gating. These findings shed light on the pairing mechanisms in Rashba superconductors and offer new pathways for developing nonlinear superconducting devices.

The principle of covariance, a cornerstone of modern physics, asserts the equivalence of all inertial frames of reference. Fluctuation theorems, as extensions of the second law of thermodynamics, establish universal connections between irreversibility and fluctuation in terms of stochastic thermodynamic quantities. However, these relations typically assume that both the thermodynamic system and the heat bath are at rest with respect to the observer, thereby failing to satisfy the principle of covariance. In this Letter, by introducing covariant work and heat that incorporate both energy-related and momentum-related components, we promote fluctuation theorems into covariant forms applicable to moving thermodynamic systems and moving heat baths. We illustrate this framework with two examples: the work statistics of a relativistic stochastic field and the heat statistics of a relativistic Brownian motion. Although our Letter is carried out in the context of special relativity, the results can be extended to the nonrelativistic limit. Our Letter combines the principle of covariance and fluctuation theorems into a coherent framework and may have applications in the study of thermodynamics relevant to cosmic microwave background as well as the radiative heat transfer and noncontact friction between relatively moving bodies.

Traditional studies of memory for meaningful narratives focus on specific stories and their semantic structures but do not address common quantitative features of recall across different narratives. We introduce a statistical ensemble of random trees to represent narratives as hierarchies of key points, where each node is a compressed representation of its descendant leaves, which are the original narrative segments. Recall from this hierarchical representation is constrained by working memory capacity. Our analytical solution aligns with observations from large-scale narrative recall experiments. Specifically, our model explains that (1) average recall length increases sublinearly with narrative length and (2) individuals summarize increasingly longer narrative segments in each recall sentence. Additionally, the theory predicts that for sufficiently long narratives, a universal, scale-invariant limit emerges, where the fraction of a narrative summarized by a single recall sentence follows a distribution independent of narrative length.

Heralded storage of photons is crucial for advancing quantum networks. Previous realizations have primarily relied on single atoms strongly coupled to optical cavities. In this work, we present the experimental realization of heralded storage using a Rydberg superatom, a mesoscopic atomic ensemble operating in the strong blockade regime. In our approach, an input photon is initially stored in the superatom via electromagnetically induced transparency. Subsequently, a second photon is emitted conditioned on the success of the first photon’s storage. Because of the collectively enhanced interaction, both the storage and the emission of the herald photon can be rather efficient in principle. As a demonstration of this technique, we use it to entangle two remote Rydberg superatoms. This method obviates the need for an intermediate node, which is commonly employed in traditional interference-based remote entanglement schemes. Our results showcase the potential of performing cavity-QED-like experiments with Rydberg superatoms. This work opens pathways for numerous applications in quantum networks and linear optical quantum computing.

Polarized neutron scattering experiments reveal anisotropy of magnetic correlations in the candidate Kitaev material $\alpha \text{−}{\mathrm{RuCl}}_3$. The anisotropy of the inelastic response at the magnetic Bragg positions is opposite to the expectation for a simple Heisenberg model. Near the antiferromagnetic propagation vector, there are no low-energy transversal magnon modes and the response is always uniaxially polarized. These observations directly prove the fully anisotropic and bond-directional character of the magnetic interaction in $\alpha \text{−}{\mathrm{RuCl}}_3$. However, other findings disagree with a simple or strongly dominant Kitaev component.

Decay properties of the neutron-deficient Sg isotopes were studied at the gas-filled recoil separator TASCA at GSI, Darmstadt by using the ${}^{52}\mathrm{Cr}+{}^{206,208}\mathrm{Pb}$ reactions. We report on the discovery of the new isotope ${}^{257}\mathrm{Sg}$. Its ground state, tentatively assigned to have $9/2^{-}$[734] configuration, was observed to decay by both spontaneous fission and $\alpha$-particle emission with a half-life of ${12.6}_{-2.3}^{+3.7}\mathrm{ms}$. The alpha decay from this high-spin state was followed by fission of ${}^{253}\mathrm{Rf}$ after $11\mathrm{\mu }\mathrm{s}$. In ${}^{259}\mathrm{Sg}$, we observed strong evidence for the occurrence of a $K$-isomeric state for the first time in superheavy nuclei with 106 protons. The current experimental findings, discussed within the experimental systematics and theory, indicate that hitherto unseen features of the shell effect on the fission process may be found in the neutron-deficient superheavy nuclei.

The dynamics of edge-core coupling is critically important to the optimization of magnetically confined fusion plasmas. Since early proposals, there has been persistent speculation that inward propagation of turbulence from the boundary is a possible means to energize the edge-core coupling region. However, the detailed mechanism of this process has remained a mystery until recent experiments observed that regular, intense gradient relaxation events generated blob-void pairs very close to the last closed flux surface. Blobs ($\tilde{n}>0$) propagate outward and detach from the bulk plasma, while voids ($\tilde{n}<0$) propagate inward, and so stir the core plasma. Here, we demonstrate that this heretofore ignored process of void emission can drive a broad turbulent layer of width $\sim 100{\rho }_s$, for typical parameters. The mechanism is the Cherenkov emission of drift waves from inward-propagating voids. The model shows promise to resolve several questions surrounding the shortfall problem and the strong turbulence in the edge-core coupling region.

Nonlinearities in King plots (KP) of isotope shifts (IS) can reveal the existence of beyond-standard-model (BSM) interactions that couple electrons and neutrons. However, it is crucial to distinguish higher-order standard model (SM) effects from BSM physics. We measure the IS of the transitions ${{}^{3}P}_0\to {{}^{3}P}_1$ in ${\mathrm{Ca}}^{14+}$ and ${{}^{2}S}_{1/2}\to {}^2{D}_{5/2}$ in ${\mathrm{Ca}}^{+}$ with sub-Hz precision as well as the nuclear mass ratios with relative uncertainties below $4\times {10}^{-11}$ for the five stable, even isotopes of calcium (${}^{40,42,44,46,48}\mathrm{Ca}$). Combined, these measurements yield a calcium KP nonlinearity with a significance of $\sim {10}^3\sigma$. Precision calculations show that the nonlinearity cannot be fully accounted for by the expected largest higher-order SM effect, the second-order mass shift, and identify the little-studied nuclear polarization as the only remaining SM contribution that may be large enough to explain it. Despite the observed nonlinearity, we improve existing KP-based constraints on a hypothetical Yukawa interaction for most of the new boson masses between $10\mathrm{eV}/{\mathrm{c}}^2$ and ${10}^7\mathrm{eV}/{\mathrm{c}}^2$.

We report the structure of a modulated phase in the ferroelectric nematic material RM734 under cationic-polymer-coated planar confinement. This phase emerges continuously from the nematic phase upon cooling and transforms into the ferroelectric nematic phase via a first-order transition. Compelling optical evidence, including thickness-dependent periodicity, a sinusoidal variation of the orientation angle, and periodic variations in phase retardance and image intensity, demonstrates that this modulated phase is the theoretically predicted double splay nematic phase. In this phase, splay deformations alternate along two orthogonal directions oriented at 45° to the substrate surfaces, resulting in a maximum modulation wavelength twice the cell thickness. Our experiments with various ionic coatings reveal that only cationic polymer coatings effectively promote this phase configuration, highlighting the crucial role of electrical screening. These findings further provide insights into its distinctive topological defects within confined geometries.

Several small polycyclic aromatic hydrocarbons (PAHs) with closed-shell electronic structure have been identified in the cold, dark environment Taurus Molecular Cloud 1. We measure efficient radiative cooling through the combination of recurrent fluorescence (RF) and IR emission in the closed-shell indenyl cation (${\mathrm{C}}_9{\mathrm{H}}_7^{+}$), finding good agreement with a master equation model including molecular dynamics trajectories to describe internal-energy-dependent properties for RF. We find that ${\mathrm{C}}_9{\mathrm{H}}_7^{+}$ formed with up to $E_c=5.85\mathrm{eV}$ vibrational energy, which is $\approx 2\mathrm{eV}$ above the dissociation threshold, radiatively cool rather than dissociate. The efficient radiative stabilization dynamics are likely common to other closed-shell PAHs present in space, contributing to their abundance.

Two-dimensional Dirac semimetals feature flatband edge states but a zero Chern number, while Chern insulators support one-way edge states associated with a nonzero Chern number. Here, we demonstrate a two-dimensional photonic crystal combining the response of a semimetal and of a Chern insulator, termed a Chern semimetal. This photonic semimetal is characterized by a nonzero Chern number, simultaneously hosting both a flatband edge state and a one-way edge state. We experimentally realize such a photonic Chern semimetal using a gyromagnetic photonic crystal with programmable magnetic bias, tailoring its second-neighbor coupling within each sublattice. We also verify the ability to control over the light speed while preserving topological protection. Our findings open new avenues toward exploring topological phases and their applications across fermionic and bosonic systems, providing an exciting platform for nanophotonic applications and a playground for topological physics discoveries.

Indentation tests are classical tools to determine material properties. For biological samples such as cysts of cells, however, the observed force-displacement relation cannot be expected to follow predictions for simple materials. Here, by solving the Pogorelov problem of a point force indenting an elastic shell for a purely nonlinear material, we discover that complex material behavior can even give rise to new scaling exponents in this force-displacement relation. In finite-element simulations, we show that these exponents are surprisingly robust, persisting even for thick shells indented with a sphere. By scaling arguments, we generalize our results to pressurized and prestressed shells, uncovering additional new scaling exponents. We find these predicted scaling exponents in the force-displacement relation observed in cyst indentation experiments. Our results thus form the basis for inferring the mechanisms that set the mechanical properties of these biological materials.

We perform three-photon photoassociation to obtain high resolution spectra of ${}^{87}\mathrm{Rb}$ trilobite dimers for the principal quantum numbers $n=22$, 24, 25, 26, and 27. The large binding energy of the molecules in combination with a relative spectroscopic resolution of ${10}^{-4}$ provides a rigorous benchmark for existing theoretical models. A recently developed Green’s function framework, which circumvents the convergence issues that afflicted previous studies, is employed to theoretically reproduce the vibrational spectrum of the molecule with high accuracy. The relatively large molecular binding energy is primarily determined by the low-energy $S$-wave electron-atom scattering length, thereby allowing us to extract the ${}^3{S}_1$ scattering phase shift with unprecedented accuracy, at low-energy regimes inaccessible to free electrons.