Interfacial magnetic anisotropy in magnetic insulators has been largely unexplored. Recently, interface-induced skyrmions and electrical control of magnetization have been discovered in insulator-based heterostructures, which demand a thorough understanding of interfacial interactions in these materials. We observe a substantial, tunable interfacial magnetic anisotropy between ${\mathrm{Tm}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ epitaxial thin films and fifteen nonmagnetic materials spanning a significant portion of the periodic table, which we attribute to Rashba spin-orbit coupling. Our results show a clear distinction between nonmagnetic capping layers from the $d$ block and the $p$ block. This work offers a new path for controlling magnetic phases in magnetic insulators for low-loss spintronic applications.

In silicon quantum dots (QDs), at a certain magnetic field commonly referred to as the “hot spot,” the electron spin relaxation rate ($T_1^{-1}$) can be drastically enhanced due to strong spin-valley mixing. Here, we experimentally find that with a valley splitting of $78.2\pm 1.6\mu \mathrm{eV}$, this hot spot in spin relaxation can be suppressed by more than 2 orders of magnitude when the in-plane magnetic field is oriented at an optimal angle, about 9° from the [100] sample plane. This directional anisotropy exhibits a sinusoidal modulation with a 180° periodicity. We explain the magnitude and phase of this modulation using a model that accounts for both spin-valley mixing and intravalley spin-orbit mixing. The generality of this phenomenon is also confirmed by tuning the electric field and the valley splitting up to $268.5\pm 0.7\mu \mathrm{eV}$.

In ergodic many-body quantum systems, locally encoded quantum information becomes, in the course of time evolution, inaccessible to local measurements. This concept of “scrambling” is currently of intense research interest, entailing a deep understanding of many-body dynamics such as the processes of chaos and thermalization. Here, we present first experimental demonstrations of quantum information scrambling on a 10-qubit trapped-ion quantum simulator representing a tunable long-range interacting spin system, by estimating out-of-time ordered correlators (OTOCs) through randomized measurements. We also analyze the role of decoherence in our system by comparing our measurements to numerical simulations and by measuring Rényi entanglement entropies.

If time is described by a fundamental process rather than a coordinate, it interacts with any physical system that evolves in time. The resulting dynamics is shown here to be consistent provided the fundamental period of the time system is sufficiently small. A strong upper bound $T_C<{10}^{-33}\mathrm{s}$ of the fundamental period of time, several orders of magnitude below any direct time measurement, is obtained from bounds on dynamical variations of the period of a system evolving in time.

The nitrogen-vacancy (NV) center is a potential atomic-scale spin sensor for electric field sensing. However, its natural susceptibility to the magnetic field hinders effective detection of the electric field. Here we propose a robust electrometric method utilizing continuous dynamic decoupling (CDD) technique. During the CDD period, the NV center evolves in a dressed frame, where the sensor is resistant to magnetic fields but remains sensitive to electric fields. As an example, we use this method to isolate the electric noise from a complex electromagnetic environment near diamond surface via measuring the dephasing rate between dressed states. By reducing the surface electric noise with different covered liquids, we observe an unambiguous relation between the dephasing rate and the relative dielectric permittivity of the liquid, which enables a quantitative investigation of electric noise model near the diamond surface.

The St. Petersburg paradox provides a simple paradigm for systems that show sensitivity to rare events. Here, we demonstrate a physical realization of this paradox using tensile fracture, experimentally verifying for six decades of spatial and temporal data and two different materials that the fracture force depends logarithmically on the length of the fiber. The St. Petersburg model may be useful in a variety fields where failure and reliability are critical.

We sandwich a colloidal gel between two parallel plates and induce a radial flow by lifting the upper plate at a constant velocity. Two distinct scenarios result from such a tensile test: (i) stable flows during which the gel undergoes a tensile deformation without yielding, and (ii) unstable flows characterized by the radial growth of air fingers into the gel. We show that the unstable regime occurs beyond a critical energy input, independent of the gel’s macroscopic yield stress. This implies a local fluidization of the gel at the tip of the growing fingers and results in the most unstable wavelength of the patterns exhibiting the characteristic scalings of the classical viscous fingering instability. Our work provides a quantitative criterion for the onset of fingering in colloidal gels based on a local shear-induced yielding in agreement with the delayed failure framework.

We consider the number distribution of topological defects resulting from the finite-time crossing of a continuous phase transition and identify signatures of universality beyond the mean value, predicted by the Kibble-Zurek mechanism. Statistics of defects follows a binomial distribution with $\mathcal{N}$ Bernouilli trials associated with the probability of forming a topological defect at the locations where multiple domains merge. All cumulants of the distribution are predicted to exhibit a common universal power-law scaling with the quench time in which the transition is crossed. Knowledge of the distribution is used to discuss the onset of adiabatic dynamics and bound rare events associated with large deviations.

Strongly interacting two-dimensional Fermi systems are one of the great remaining challenges in many-body physics due to the interplay of strong local correlations and enhanced long-range fluctuations. Here, we probe the thermodynamic and transport properties of a 2D Fermi gas across the BEC-BCS crossover by studying the propagation and damping of sound modes. We excite particle currents by imprinting a phase step onto homogeneous Fermi gases trapped in a box potential and extract the speed of sound from the frequency of the resulting density oscillations. We measure the speed of sound across the BEC-BCS crossover and compare the resulting dynamic measurement of the equation of state both to a static measurement based on recording density profiles and to quantum Monte Carlo calculations and find reasonable agreement between all three. We also measure the damping of the sound mode, which is determined by the shear and bulk viscosities as well as the thermal conductivity of the gas. We find that the damping is minimal in the strongly interacting regime and the diffusivity approaches the universal quantum bound $\hslash /m$ of a perfect fluid.

We investigate the number entropy $S_N$—which characterizes particle-number fluctuations between subsystems—following a quench in one-dimensional interacting many-body systems with potential disorder. We find evidence that in the regime which is expected to show many-body localization and where the entanglement entropy grows as $S\sim \ln t$ as function of time $t$, the number entropy grows as $S_N\sim \ln \ln t$, indicating continuing subdiffusive particle transport at a very slow rate. We demonstrate that this growth is consistent with a relation between entanglement and number entropy recently established for noninteracting systems.

Densest possible packings of identical spheroids in cylindrical confinement have been obtained through Monte Carlo simulations. By varying the shape anisotropy of spheroids and also the cylinder-to-spheroid size ratio, a variety of densest possible crystalline structures have been discovered, including achiral structures with specific orientations of particles and chiral helical structures with rotating orientations of particles. Our findings reveal a transition between confinement-induced chiral ordering and shape-anisotropy-induced orientational ordering and would serve as a guide for the fabrication of crystalline wires using anisotropic particles.

Since pulsars were discovered as emitters of bright coherent radio emission more than half a century ago, the cause of the emission has remained a mystery. In this Letter we demonstrate that coherent radiation can be directly generated in nonstationary pair plasma discharges which are responsible for filling the pulsar magnetosphere with plasma. By means of large-scale two-dimensional kinetic plasma simulations, we show that if pair creation is nonuniform across magnetic field lines, the screening of electric field by freshly produced pair plasma is accompanied by the emission of waves which are electromagnetic in nature. Using localized simulations of the screening process, we identify these waves as superluminal ordinary ($O$) modes, which should freely escape from the magnetosphere as the plasma density drops along the wave path. The spectrum of the waves is broadband and the frequency range is comparable to that of observed pulsar radio emission.

Interfacing bulk conducting topological ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ films with $s$-wave superconductors initiates strong superconducting order in the nontrivial surface states. However, bulk insulating topological ${({\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x)}_2{\mathrm{Te}}_3$ films on bulk Nb instead exhibit a giant attenuation of surface superconductivity, even for films only two layers thick. This massive suppression of proximity pairing is evidenced by ultrahigh-resolution band mappings and by contrasting quantified superconducting gaps with those of heavily $n$-doped topological ${\mathrm{Bi}}_2{\mathrm{Se}}_3/\mathrm{Nb}$. The results underscore the limitations of using superconducting proximity effects to realize topological superconductivity in nearly intrinsic systems.

The electron-phonon interaction (EPI) is instrumental in a wide variety of phenomena in solid-state physics, such as electrical resistivity in metals, carrier mobility, optical transition, and polaron effects in semiconductors, lifetime of hot carriers, transition temperature in BCS superconductors, and even spin relaxation in diamond nitrogen-vacancy centers for quantum information processing. However, due to the weak EPI strength, most phenomena have focused on electronic properties rather than on phonon properties. One prominent exception is the Kohn anomaly, where phonon softening can emerge when the phonon wave vector nests the Fermi surface of metals. Here we report a new class of Kohn anomaly in a topological Weyl semimetal (WSM), predicted by field-theoretical calculations, and experimentally observed through inelastic x-ray and neutron scattering on WSM tantalum phosphide. Compared to the conventional Kohn anomaly, the Fermi surface in a WSM exhibits multiple topological singularities of Weyl nodes, leading to a distinct nesting condition with chiral selection, a power-law divergence, and non-negligible dynamical effects. Our work brings the concept of the Kohn anomaly into WSMs and sheds light on elucidating the EPI mechanism in emergent topological materials.

The unconventional thermal properties of jammed amorphous solids are directly related to their density of vibrational states. While the vibrational spectrum of jammed soft sphere solids has been fully described, the vibrational spectrum of hard spheres, a model glass former often related to physical colloidal glasses, is still unknown due to the difficulty of treating the nonanalytic interaction potential. We bypass this difficulty using the recently described effective interaction potential for the free energy of thermal hard spheres. By minimizing this effective free energy, we mimic the rapid compression of hard spheres and produce typical configurations of the thermal system. We measure the resulting vibrational spectrum and characterize its evolution toward the jamming point where configurations of hard and soft spheres are trivially unified. For densities approaching jamming from below, we observe low-frequency modes which agree with those found in numerical simulations of jammed soft spheres. Our measurements of the vibrational structure demonstrate that the jamming universality extends away from jamming: hard sphere thermal systems below jamming exhibit the same vibrational spectra as thermal and athermal soft sphere systems above the transition.

We experimentally investigate the effects of the linear photon momentum on the momentum distributions of photoions and photoelectrons generated in one-photon ionization in an energy range of $300\mathrm{eV}\le E_{\gamma }\le 40\mathrm{keV}$. Our results show that for each ionization event the photon momentum is imparted onto the photoion, which is essentially the system’s center of mass. Nevertheless, the mean value of the ion momentum distribution along the light propagation direction is backward-directed by $-3/5$ times the photon momentum. These results experimentally confirm a 90-year-old prediction.

Size-dependent yield strength is a common feature observed in miniaturized crystalline metallic samples, and plenty of studies have been conducted in experiments and numerical simulations to explore the underlying mechanism. However, the transition in yield strength from bulklike to size-affected behavior has received less attention. Here a unified theoretical model is proposed to probe the yield strength of crystalline metallic materials with sample size from nanoscale to macroscale. We show that the transition in yield strength versus size can be fully explained by the competition between the stresses required for dislocation source activation and dislocation motion, which is regulated by dislocation density, irradiation defect, grain boundary, and so on. Based on various grain boundary densities, the extended Hall–Petch relation, incorporated into the unified model, captures the reverse size effect for polycrystalline samples. The proposed model predictions agree well with reported experimental measurements of various specimens, including the prestrained nickel, irradiated copper, ultrafine grain tungsten, and so on.

The angular momentum of evanescent light fields has been studied in nano-optics and plasmonics but not in the microwave regime. Here we predict noncontact pumping of electron spin currents in conductors by the evanescent stray fields of excited magnetic nanostructures. The coherent transfer of the photon to the electron spin is proportional to the $g$ factor, which is large in narrow gap semiconductors and surface states of topological insulators. The spin pumping current is chiral when the spin susceptibility displays singularities that indicate collective states. However, 1D systems with linear dispersion at the Fermi energy, such as metallic carbon nanotubes, are an exception since spin pumping is chiral even without interactions.

Surface processes on cosmic solids in cold astrophysical environments lead to gas-phase depletion and molecular complexity. Most astrophysical models assume that the molecular ice forms a thick multilayer substrate, not interacting with the dust surface. In contrast, we present experimental results demonstrating the importance of the surface for porous grains. We show that cosmic dust grains may be covered by a few monolayers of ice only. This implies that the role of dust surface structure, composition, and reactivity in models describing surface processes in cold interstellar, protostellar, and protoplanetary environments has to be reevaluated.

The ${\mathrm{\Lambda }}_c^{+}{K}^{-}$ mass spectrum is studied with a data sample of $pp$ collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of $5.6{\mathrm{fb}}^{-1}$ collected by the LHCb experiment. Three ${\mathrm{\Xi }}_c^0$ states are observed with a large significance and their masses and natural widths are measured to be $m[{\mathrm{\Xi }}_c(2923{)}^0]=2923.04\pm 0.25\pm 0.20\pm 0.14\mathrm{MeV}$, $\mathrm{\Gamma }[{\mathrm{\Xi }}_c(2923{)}^0]=7.1\pm 0.8\pm 1.8\mathrm{MeV}$, $m[{\mathrm{\Xi }}_c(2939{)}^0]=2938.55\pm 0.21\pm 0.17\pm 0.14\mathrm{MeV}$, $\mathrm{\Gamma }[{\mathrm{\Xi }}_c(2939{)}^0]=10.2\pm 0.8\pm 1.1\mathrm{MeV}$, $m[{\mathrm{\Xi }}_c(2965{)}^0]=2964.88\pm 0.26\pm 0.14\pm 0.14\mathrm{MeV}$, $\mathrm{\Gamma }[{\mathrm{\Xi }}_c(2965{)}^0]=14.1\pm 0.9\pm 1.3\mathrm{MeV}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the ${\mathrm{\Lambda }}_c^{+}$ mass. The ${\mathrm{\Xi }}_c(2923{)}^0$ and ${\mathrm{\Xi }}_c(2939{)}^0$ baryons are new states. The ${\mathrm{\Xi }}_c(2965{)}^0$ state is in the vicinity of the known ${\mathrm{\Xi }}_c(2970{)}^0$ baryon; however, their masses and natural widths differ significantly.