We study the dynamical response of viscous materials to gravitational waves, in the context of a fully relativistic theory of fluid dynamics. For the first time, we calculate oscillation modes and scattering properties of viscous stars. Viscous stars absorb high-frequency radiation, following a dispersion relation introduced by Press. In the extremely large viscosity regime, stars would become reflectors of waves, but this regime appears to be forbidden by causality bounds. In the context of black hole mimickers, we show how maximally viscous stars on the threshold of stability mimic the absorption of a black hole with the same mass. Our results suggest that rotating viscous stars will amplify incoming radiation.

We present an experimental study of the flow regime and vortex structure in bulk polymeric turbulence through three-dimensional velocity measurements with unprecedented high spatial resolution. We demonstrate that, as the polymer concentration increases, the effect of polymers on the fluid energy dissipation rate can be categorized into two distinct regimes: the dissipation reduction regime and the maximum dissipation reduction (MDR) regime, and in the latter the effect of the polymers saturates. We reveal that the MDR regime occurs when the scale range affected by the polymer additives extends up to the integral length scale, rather than the generally accepted Lumley scale. This finding enables us to map out the phase diagram of the flow regimes of polymeric turbulence on the Reynolds number and Weissenberg number. Furthermore, we demonstrate that in the MDR regime, sheetlike vortex and strain structures dominate, which is traced to the fact that polymer stress stabilizes shear layers and reduces perturbation to shear instability. These results suggest that the MDR regime is a universal flow state in bulk polymeric turbulence and is the counterpart of the maximum drag reduction regime in wall-bounded flows. Our findings emphasize the significance of sheetlike vortex structures and offer new insights into predicting the critical conditions for the emergence of various flow regimes in viscoelastic fluids.

We present optical fiber experiments investigating the perturbed, nonintegrable evolution of soliton gases (SGs) under weak linear damping and gain. By measuring the amplitude and phase of the optical field in a recirculating loop, we determine the spectral distribution of SGs at various propagation distances. We demonstrate that a SG, initially prepared as a soliton condensate with a Weyl distribution, undergoes significant changes in its spectral distribution due to dissipation. Specifically, weak gain leads to the emergence of a bichromatic SG, while weak damping results in a SG with a semicircular spectral distribution at long propagation distances. These observed dissipation-driven changes in the SG’s spectral characteristics are not explained by existing hydrodynamic or kinetic theories.

Understanding the transparency of two-dimensional (2D) materials to intermolecular interactions—particularly their ability to transmit van der Waals (vdW) forces—is crucial for applications such as the design of 2D material-based nanofluidic and microelectromechanical systems. However, experimental studies have produced inconsistent and even contradictory conclusions regarding the vdW transparency of 2D materials. Here, we employ colloidal atomic force microscopy with a geometrically well-defined probe to measure pull-off and pull-in forces in a model system: graphene on silicon dioxide (${\mathrm{SiO}}_2$). Our results reveal that the total vdW force deviates significantly from the naive sum of contributions from graphene and its substrate. Intriguingly, the measured pull-off forces indicate that the effective surface energy of a suspended graphene monolayer can exceed that of its substrate-supported counterpart. Furthermore, our measurements of pull-in forces in substrate-supported systems suggest that graphene of 1–5 layers screens 15%–50% of the intrinsic solid-solid vdW interaction, consistent with Lifshitz theory calculations.

Two-dimensional (2D) van der Waals (vdW) magnetic semiconductors are a new class of quantum materials for studying the emergent physics of excitons and spins in the 2D limit. Twist engineering provides a powerful tool to manipulate the fundamental properties of 2D vdW materials. Here, we show that twist engineering of the anisotropic ferromagnetic monolayer semiconductor CrSBr leads to bilayer magnetic semiconductors with continuously tunable magnetic moment, dielectric anisotropy, exciton energy, and linear dichroism. We furthermore provide a model for exciton energy in the media with tunable anisotropy. These results advance fundamental studies of 2D vdW materials and open doors to applications to nano-optics, twistronics, and spintronics.

Although the search for quantum many-body phenomena in magnetic materials has a strong focus on highly frustrated systems, even unfrustrated quantum magnets show a multitude of unconventional phenomena in their spin excitation spectra. ${\text{YbBr}}_3$ is an excellent realization of the $S=1/2$ antiferromagnetic Heisenberg model on the honeycomb lattice, and we have performed detailed spectroscopic experiments with both unpolarized and polarized neutrons at all applied magnetic fields up to saturation. We observe extensive excitation continua, which cause strong renormalization and the decay of single magnons at higher fields, while coherent features include field-induced “shadows” of the single magnons and the spectacular emergence of a rotonlike excitation. To guide and interpret our experiments, we performed systematic calculations by the method of cylinder matrix-product states that provide quantitative agreement with the neutron scattering data and a qualitative benchmark for the spectral signatures of strong quantum fluctuations even in the absence of magnetic frustration.

Many magnetic materials are predicted to exhibit bosonic topological edge modes in their excitation spectra, because of the nontrivial topology of their magnon, triplon, or other quasiparticle band structures. However, there is a discrepancy between theory prediction and experimental observation, which suggests some underlying mechanism that intrinsically suppresses the expected experimental signatures, like the thermal Hall current. Many-body interactions that are not accounted for in the noninteracting quasiparticle picture are most often identified as the reason for the absence of the topological edge modes. Here we report persistent bosonic edge modes at the boundaries of a ladder quantum paramagnet with gapped triplon excitations in the presence of the full many-body interaction. We use tensor network methods to resolve topological edge modes in the time-dependent spin-spin correlations and the dynamical structure factor, which is directly accessible experimentally. We further show that signatures of these edge modes survive even when the noninteracting quasiparticle theory breaks down; we discuss the topological phase diagram of the model, demonstrate the fractionalization of its low-lying excitations, and propose potential material candidates.

The generation of pure spin currents is critical for low-dissipation spintronic applications, yet existing methods relying on spin-orbit coupling or ferromagnetic interfaces face challenges in material compatibility and operational robustness. We propose a paradigm-shifting approach to generate symmetry-protected pure spin currents by applying mechanical stress on insulating antiferromagnetic materials, i.e., the pure piezospintronic effect. We first classify magnetic point groups enabling pure piezospintronic effects. A novel first-principles method is developed to compute the spin dipole moments and coefficients of the piezospintronic effect. Integrating these methodologies with high-throughput screening, we identify FeOOH, ${\mathrm{Cr}}_2{\mathrm{O}}_3$, and NaMn$X$ ($X=\mathrm{As}$, Bi, P, Sb) with significant pure piezospintronic effects. Interestingly, we reveal that the ionic displacement contribution dominates the piezospintronic effect, in contrast to the piezoelectric effect. Our study not only provides a first-principles approach for investigating spin dipole moment related phenomena (e.g., ferrotoroidicity, fractional quantum spin dipole moment, piezospintronics), but also provides promising piezospintronic materials for experimental verification and industrial applications.

${\mathrm{F}}_1$-ATPase (${\mathrm{F}}_1$) is central to cellular energy transduction. Forcibly rotated by another motor ${\mathrm{F}}_{\mathrm{o}}$, ${\mathrm{F}}_1$ catalyzes adenosine triphosphate (ATP) synthesis by converting mechanical work into chemical free energy stored in the molecule ATP. The details of how ${\mathrm{F}}_{\mathrm{o}}$ drives ${\mathrm{F}}_1$ are not fully understood; however, evaluating efficient ways to rotate ${\mathrm{F}}_1$ could provide fruitful insights into this driving since there is a selective pressure to improve efficiency. Here, we show that rotating ${\mathrm{F}}_1$ with an angle clamp is significantly more efficient than a constant torque. Our experiments, combined with theory and simulation, indicate that the angle clamp significantly suppresses the nonequilibrium variation that contributes to the futile dissipation of input work.

On the surface of a vibrating liquid bath, instead of coalescing, a drop will continually bounce on a thin film of air between the drop and the free surface, giving rise to rich chaotic dynamics and quantum analog behavior. However, perpetual bouncing is yet to be demonstrated on a vibrating rigid solid, where the control of the drop’s motion is not limited by the bath dynamics. Here we show that vibration of an atomically smooth mica surface prolongs a drop’s hovering state by several orders of magnitude, increasing the time to wet from less than a second to several minutes. The excitation of the second spherical harmonic mode determines a transition between a bouncing state with high-amplitude rebounds, and a bound state, where the drop’s motion is locked onto the vibrating solid above a thin air layer. We further develop a coupled linear spring model, accounting for the drop’s deformation, that predicts bouncing trajectories without fitting parameters. Our results extend the scope of bouncing drop studies beyond the liquid bath and highlight the potential for precision manipulation of small liquid quantities in air.

The acceleration of electrons by surface plasma waves (SPWs) generated during the interaction of ultrashort, linearly polarized, and contrast-enhanced laser pulses at a peak intensity of $\sim 6\times {10}^{20}{\mathrm{W}\mathrm{cm}}^{-2}$ with flat, noncorrugated foils at parallel incidence (with respect to the target surface) is investigated. We experimentally demonstrate the generation of a collimated electron beam ($<0.6\mathrm{mrad}$) with a non-Maxwellian spectrum, characterized by peaks at superponderomotive energies (30–36 MeV) and total charge $\sim 120\mathrm{pC}$. Through particle-in-cell (PIC) simulations, we identify the $\mathbf{J}\times \mathbf{B}$ force at the front edge as the primary mechanism for injecting electrons into the SPW, where they are further accelerated. Furthermore, our simulation findings reveal that lateral surface contaminants influence SPW dynamics and give rise to a long-ranging plasmonic mode.

Accurately quantifying the energy loss rate of proton beams in liquid water is crucial for the precise application and improvement of proton therapy, whereas the slowing down of protons in water ices also plays an important role in astrophysics. However, precisely determining the electronic stopping power, particularly for the liquid phase, has been elusive so far. Experimental techniques are difficult to apply to volatile liquids, and the availability of sufficient reliable measurements has been limited to the solid and vapor phases. The accuracy of current models is typically limited to proton energies just above the energy loss maximum, making it difficult to predict radiation effects at an energy range of special relevance. We elucidate the phase differences in proton energy loss in water in a wide energy range ($0.001-10\mathrm{MeV}$) by means of real-time time-dependent density functional theory combined with the Penn method. This nonperturbative model, more computationally efficient than current approaches, describes the phase effects in water in excellent agreement with available experimental data, revealing clear deviations around the maximum of the stopping power curve and below. As an important outcome, our calculations reveal that proton stopping quantities of liquid water and amorphous ice are identical, in agreement with recent similar observations for low-energy electrons, pointing out this equivalence for all charged particles. This could help to overcome the limitation in obtaining reliable experimental information for the biologically relevant liquid water target.

We explore the potential of using late-time galaxy spins to test the parity symmetry of primordial vector fossils. Using $N$-body simulations, we analyze halo spins as a reliable proxy for galaxy spins to investigate the detectability of this effect. We develop a novel approach to generate initial conditions (ICs) that have substantial parity asymmetry but do not alter the initial matter power spectrum. We construct the initial spin fields from the parity broken ICs and halo spin fields using late-time halos evolved from such ICs. Focusing on the helicity of these vector fields, we detect substantial asymmetry in the initial spin field. In addition, we find that over 50% of the initial spin field’s asymmetry remains in the late-time halo spin field on a range of scales. Based on mock galaxy spin fields derived from the halo spin fields, we forecast that a maximum detection at $13\sigma$ is possible with the final DESI BGS for the model considered in this analysis. Our findings demonstrate that primordial vectorial parity violation survives nonlinear gravitational evolution, and thus, can be effectively probed with galaxy spins at late times.

Kelvin probe force microscopy (KPFM) is widely used in stationary and dynamic studies of contact electrification. An obvious question that connects these two has been overlooked: when are charge dynamics too fast for stationary studies to be meaningful? Using a rapid transfer system to quickly perform KPFM after contact, we find the dynamics are too fast in all but the best insulators. Our data further suggest that dynamics are caused by bulk as opposed to surface conductivity, and that charge-transfer heterogeneity is less prevalent than previously suggested.

The determination of the absolute neutrino mass scale remains a fundamental open question in particle physics, with profound implications for both the standard model and cosmology. Direct kinematic measurements, independent of model-dependent assumptions, provide the most robust approach to address this challenge. Here we present the most stringent upper bound on the effective electron neutrino mass ever obtained with a calorimetric measurement of the electron capture decay of ${}^{163}\mathrm{Ho}$. The HOLMES experiment employs an array of ion-implanted transition-edge sensor (TES) microcalorimeters, achieving an average energy resolution of 6 eV FWHM with a scalable, multiplexed readout technique. With a total of $7\times {10}^7$ decay events recorded over two months and a Bayesian statistical analysis, we derive an upper limit of $m_{\beta }<27\mathrm{eV}/c^2$ at 90% credibility. These results validate the feasibility of ${}^{163}\mathrm{Ho}$ calorimetry for next-generation neutrino mass experiments and demonstrate the potential of a scalable TES-based microcalorimetric technique to push the sensitivity of direct neutrino mass measurements beyond the current state of the art.

We report precision measurements on cumulants ($C_n$) and factorial cumulants (${\kappa }_n$) of (net) proton number distributions up to fourth order in $\mathrm{Au}+\mathrm{Au}$ collisions over center-of-mass energies $\sqrt{s_{NN}}=7.7–27\mathrm{GeV}$ from phase II of the Beam Energy Scan program at RHIC. (Anti)protons are selected at midrapidity ($|y|<0.5$) within a transverse momentum range of $0.4<p_T<2.0\mathrm{GeV}/c$. Relative to various noncritical-point model calculations and peripheral collision 70%–80% data, the net proton $C_4/C_2$ measurement in 0%–5% collisions shows a minimum around 19.6 GeV for significance of deviation at $\sim 2–5\sigma$. A minimum in $C_4/C_2$ with respect to a noncritical baseline is expected to be a characteristic feature of the signature associated with a critical point in the QCD phase diagram. In addition, deviations from noncritical baselines around the same collision energy region are also seen in proton factorial cumulant ratios, especially in ${\kappa }_2/{\kappa }_1$ and ${\kappa }_3/{\kappa }_1$. Dynamical model calculations including a critical point are called for in order to understand these precision measurements.

We present a response-augmented machine-learning (ML) approach to the energetics of electrified metal surfaces. We leverage local descriptors to learn the work function as the first-order energy change to introduced bias charges and stabilize this learning through Born effective charges. This permits the efficient extension of ML interatomic potential architectures to include finite bias effects up to second order. Application to OH at Cu(100) rationalizes the experimentally observed $p\mathrm{H}$ dependence of the preferred adsorption site in terms of a non-Nernstian charge-induced site switching.

Graphene-based moiré superlattices provide a versatile platform for exploring novel correlated and topological electronic states, driven by enhanced Coulomb interactions within flat bands. The intrinsic tunability of graphene’s multiple degrees of freedom enables precise control over these complex quantum phases. In this study, we observe a range of competing phases and their transitions in rhombohedral stacked hexalayer graphene on hexagonal boron nitride ($r\text{−}6\mathrm{G}/\mathrm{hBN}$) moiré superlattices. When electrons are polarized away from the moiré superlattice, we first identify a Chern insulator with reversible Chern numbers at $v=1$ (one electron per moiré cell), revealing a competition between bulk and edge orbital magnetization. At $v=2$, three distinct insulating phases—spin-antiferromagnetic, spin-polarized, and valley-polarized—emerge under vertical displacement field $D$ and magnetic field $B_{\perp }$, governed by hierarchical isospin symmetry breaking. Furthermore, charge density wave (CDW) states at $\nu =1/3$ and $2/3$, along with a magnetic-field-induced stripe phase at $\nu =1/2$, demonstrate tunable correlated orders at fractional fillings. Our findings reveal a rich interplay of charge, isospin, topology, and magnetic field in rhombohedral graphene moiré superlattices.

Entanglement is the cornerstone of quantum communication, yet conventional detection relies solely on local measurements. In this Letter, we present an experimental demonstration, based on an improved theoretical framework showing that one-way local operations and classical communication (1-LOCC) can significantly outperform purely local measurements in detecting quantum entanglement. By casting the entanglement detection problem as a semidefinite program, we derive protocols that minimize false negatives at fixed false-positive rates. A variational generative machine-learning algorithm efficiently searches over high-dimensional parameter spaces, identifying states and measurement strategies that exhibit a clear 1-LOCC advantage. Experimentally, we realize a genuine event-ready protocol on a three-dimensional photonic entanglement source, employing fiber delays as short-lived quantum memories. We implement rapid, field-programmable gate array-based sampling of the optimized probabilistic instructions, allowing Bob’s measurement settings to adapt to Alice’s outcomes in real time. Our results validate the predicted 1-LOCC advantage in a realistic noisy setting and reduce the experimental trials needed to certify entanglement. These findings mark a step toward scalable, adaptive entanglement detection methods crucial for quantum networks and computing, paving the way for more efficient generation and verification of high-dimensional entangled states.

We present a theory for the relaxation time of the octupole order parameter in nanoscale chiral antiferromagnets (AFMs) coupled to thermal baths and spin injection sources. Using stochastic spin dynamics simulations, we demonstrate that the octupole moment relaxes through two distinct mechanisms—escape over a barrier and precessional dephasing—as the barrier for octupole fluctuations is lowered relative to the thermal energy. Notably, the octupole moment relaxes orders of magnitude faster than the typical dipolar order parameters, reaching picosecond timescales. By combining Langer’s theory with an effective low-energy description of octupole dynamics in chiral AFMs, we derive analytical expressions for the relaxation times. We find that relaxation in chiral AFMs parallels dipole relaxation in $XY$ magnets, with exchange fields serving the role of the dipole fields. Further, by drawing on the analogy between order parameter dynamics in $XY$ magnets under spin injection and current-biased Josephson junctions, we propose a new scheme for electrically tuning the octupole relaxation times. Our Letter offers fundamental insights for the development of next-generation spintronic devices that harness octupole order parameters for information encoding.