Vortex rings are ubiquitous topological structures in nature. In solid magnetic systems, their formation leads to intriguing physical phenomena and potential device applications. However, realizing these topological magnetic vortex rings and manipulating their topology on demand have still been challenging. Here, we theoretically show that topological vortex rings can be created by a current pulse in a chiral magnetic nanocylinder with a trench structure. The creation process involves the formation of a vortex ring street, i.e., a chain of magnetic vortex rings with an alternative linking manner. The created vortex rings can be bounded with monopole-antimonopole pairs and possess a rich and controllable linking topology (e.g., Hopf link and Solomon link), which is determined by the duration and amplitude of the current pulse. Our proposal paves the way for the realization and manipulation of diverse three-dimensional (3D) topological spin textures and could catalyze the development of 3D spintronic devices.

Moiré-pattern-based potential engineering has become an important way to explore exotic physics in a variety of two-dimensional condensed matter systems. While these potentials have induced correlated phenomena in almost all commonly studied 2D materials, monolayer graphene has remained an exception. We demonstrate theoretically that a single layer of graphene, when placed between two bulk boron nitride crystal substrates with the appropriate twist angles, can support a robust topological ultraflat band emerging as the second hole band. This is one of the simplest platforms to design and exploit topological flat bands.

A search is reported for near-threshold structures in the $J/\psi J/\psi$ invariant mass spectrum produced in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ from data collected by the CMS experiment, corresponding to an integrated luminosity of $135{\mathrm{fb}}^{-1}$. Three structures are found, and a model with quantum interference among these structures provides a good description of the data. A new structure is observed with a local significance above 5 standard deviations at a mass of ${6638}_{-38}^{+43}{(\mathrm{stat})}_{-31}^{+16}(\mathrm{syst})\mathrm{MeV}$. Another structure with even higher significance is found at a mass of ${6847}_{-28}^{+44}{(\mathrm{stat})}_{-20}^{+48}(\mathrm{syst})\mathrm{MeV}$, which is consistent with the $X(6900)$ resonance reported by the LHCb experiment and confirmed by the ATLAS experiment. Evidence for another new structure, with a local significance of 4.7 standard deviations, is found at a mass of ${7134}_{-25}^{+48}{(\mathrm{stat})}_{-15}^{+41}(\mathrm{syst})\mathrm{MeV}$. Results are also reported for a model without interference, which does not fit the data as well and shows mass shifts up to 150 MeV relative to the model with interference.

We present a novel method to measure the arrival time statistics of continuous electron beams with subpicosecond resolution, based on the combination of an rf deflection cavity and fast single electron imaging. We observe Poissonian statistics within time bins from 100 to 2 ns and increasingly pronounced sub-Poissonian statistics as the time bin decreases from 2 ps to 340 fs. This 2D streak camera, in principle, enables femtosecond-level arrival time measurements, paving the way to observing Pauli blocking effects in electron beams and thus serving as an essential diagnostic tool toward degenerate electron beam sources for free-electron quantum optics.

Many systems, when initially placed far from equilibrium, exhibit surprising behavior in their attempt to equilibrate. Striking examples are the Mpemba effect and the cooling-heating asymmetry. These anomalous behaviors can be exploited to shorten the time needed to cool down (or heat up) a system. Though, a strategy to design these effects in mesoscopic systems is missing. We bring forward a description that allows us to formulate such strategies, and, along the way, makes natural these paradoxical behaviors. In particular, we study the evolution of macroscopic physical observables of systems freely relaxing under the influence of one or two instantaneous thermal quenches. The two crucial ingredients in our approach are timescale separation and a nonmonotonic temperature evolution of an important state function. We argue that both are generic features near a first-order transition. Our theory is exemplified with the one-dimensional Ising model in a magnetic field using analytic results and numerical experiments.

When studying interacting systems, computing their statistical properties is a fundamental problem in various fields such as physics, applied mathematics, and machine learning. However, this task can be quite challenging due to the exponential growth of the state space as the system size increases. Many standard methods have significant weaknesses. For instance, message-passing algorithms can be inaccurate and even fail to converge due to short loops, while tensor network methods can have exponential computational complexity in large graphs due to long loops. In this Letter, we propose a new method called “tensor network message passing.” This approach allows us to compute local observables like marginal probabilities and correlations by combining the strengths of tensor networks in contracting small subgraphs with many short loops and the strengths of message-passing methods in globally sparse graphs, thus addressing the crucial weaknesses of both approaches. Our algorithm is exact for systems that are globally treelike and locally dense-connected when the dense local graphs have a limited tree width. We have conducted numerical experiments on synthetic and real-world graphs to compute magnetizations of Ising models and spin glasses, and have demonstrated the superiority of our approach over standard belief propagation and the recently proposed loopy message-passing algorithm. In addition, we discuss the potential applications of our method in inference problems in networks, combinatorial optimization problems, and decoding problems in quantum error correction.

Magnetic reconnection drives multispecies particle acceleration broadly in space and astrophysics. We perform the first 3D hybrid simulations (fluid electrons, kinetic ions) that contain sufficient scale separation to produce nonthermal heavy-ion acceleration, with fragmented flux ropes critical for accelerating all species. We demonstrate the acceleration of all ion species (up to Fe) into power-law spectra with similar indices, by a common Fermi acceleration mechanism. The upstream ion velocities influence the first Fermi reflection for injection. The subsequent onsets of Fermi acceleration are delayed for ions with lower charge-mass ratios ($\mathrm{Q}/\mathrm{M}$), until growing flux ropes magnetize them. This leads to a species-dependent maximum energy/nucleon $\propto (Q/M{)}^{\alpha }$. These findings are consistent with in situ observations in reconnection regions, suggesting Fermi acceleration as the dominant multispecies ion acceleration mechanism.

Using Raman spectroscopy to study the correlated $4d$-electron metal ${\mathrm{Sr}}_2{\mathrm{RhO}}_4$, we observe pronounced excitations at 220 meV and 240 meV with $A_{1\mathrm{g}}$ and $B_{1\mathrm{g}}$ symmetries, respectively. We identify them as transitions between the spin-orbit multiplets of the Rh ions, in close analogy to the spin-orbit excitons in the Mott insulators ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ and $\alpha \text{−}{\text{RuCl}}_3$. This observation provides direct evidence for the unquenched spin-orbit coupling in ${\mathrm{Sr}}_2{\mathrm{RhO}}_4$. A quantitative analysis of the data reveals that the tetragonal crystal field $\mathrm{\Delta }$ in ${\mathrm{Sr}}_2{\mathrm{RhO}}_4$ has a sign opposite to that in insulating ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, which enhances the planar $xy$ orbital character of the effective $J=1/2$ wave function. This supports a metallic ground state, and suggests that $c$-axis compression of ${\mathrm{Sr}}_2{\mathrm{RhO}}_4$ may transform it into a quasi-two-dimensional antiferromagnetic insulator.

An explanation for the origin and number of clumps along the equatorial ring of Supernova 1987A has eluded decades of research. Our linear analysis and hydrodynamic simulations of the expanding ring prior to the supernova reveal that it is subject to the Crow instability between vortex cores. The dominant wave number is remarkably consistent with the number of clumps, suggesting that the Crow instability stimulates clump formation. Although the present analysis focuses on linear fluid flow, future nonlinear analysis and the incorporation of additional stellar physics may further elucidate the remnant structure and the evolution of the progenitor and other stars.

Precision measurements in Rydberg states of H with principal quantum number $n$ in the range between 20 and 30 are reported. In the presence of homogeneous electric fields with strengths below $2\mathrm{V}{\mathrm{cm}}^{-1}$, these Rydberg states are subject to a linear Stark effect with accurately calculable Stark shifts. From the spectral positions of field-independent and field-dependent Rydberg-Stark states, we derive the $n=20$ and 24 Bohr energies, and the ionization energy with respect to the $2{}^2{S}_{1/2}(f=0,1)$ [short $2S(0,1)$] metastable states. Combining these results with the $2S(1)-1S(1)$ transition frequency [C. G. Parthey et al., Phys. Rev. Lett. 107, 203001 (2011); A. Matveev et al., Phys. Rev. Lett. 110, 230801 (2013)] and the $1S$ hyperfine splitting [L. Essen et al., Nature (London) 229, 110 (1971)], we determine the ionization frequency of the $1S(0)$ ground state to be $3288087922407.2(3.7{)}_{\mathrm{stat}}(1.8{)}_{\mathrm{syst}}\mathrm{kHz}$, which is the most precise value ever determined for the binding energy of a two-body quantum system. Using the $2S(0)-2P_{1/2}(1)$ interval [N. Bezginov et al., Science 365, 1007 (2019)], we determine the Rydberg frequency to be $c{R}_{\infty }=3289841960204(15{)}_{\mathrm{stat}}(7{)}_{\mathrm{syst}}(13{)}_{2S-2P}\mathrm{kHz}$ in a procedure that is insensitive to the value of the proton charge radius. These new results are discussed in the context of the proton-size puzzle.

It has been theoretically predicted that perturbation of the Berry curvature by electromagnetic fields gives rise to intrinsic nonlinear anomalous Hall effects that are independent of scattering. Two types of nonlinear anomalous Hall effects are expected. The electric nonlinear Hall effect has recently begun to receive attention, while very few studies are concerned with the magneto-nonlinear Hall effect. Here, we combine experiment and first-principles calculations to show that the kagome ferromagnet ${\mathrm{Fe}}_3{\mathrm{Sn}}_2$ displays such a magneto-nonlinear Hall effect. By systematic field angular and temperature-dependent transport measurements, we unambiguously identify a large anomalous Hall current that is linear in both applied in-plane electric and magnetic fields, utilizing a unique in-plane configuration. We clarify its dominant orbital origin and connect it to the magneto-nonlinear Hall effect. The effect is governed by the intrinsic quantum geometric properties of Bloch electrons. Our results demonstrate the significance of the quantum geometry of electron wave functions from the orbital degree of freedom and open up a new direction in Hall transport effects.

In conventional sliding electrical contacts (SECs), large critical current density (CCD) requires a high ratio between actual and apparent contact area, while low friction and wear require the opposites. Structural superlubricity (SSL) has the characteristics of zero wear, near zero friction, and all-atoms in real contact between the contacting surfaces. Here, we show a measured current density up to $17.5\mathrm{GA}/{\mathrm{m}}^2$ between microscale graphite contact surfaces while sliding under ambient conditions. This value is nearly 146 times higher than the maximum CCD of other SECs reported in literatures ($0.12\mathrm{GA}/{\mathrm{m}}^2$). Meanwhile, the coefficient of friction for the graphite contact is less than 0.01 and the sliding interface is wear-free according to the Raman characterization, indicating the presence of the SSL state. Furthermore, we estimate the intrinsic CCD of single crystalline graphite to be $6.69\mathrm{GA}/{\mathrm{m}}^2$ by measuring the scaling relation of CCD. Theoretical analysis reveals that the CCD is limited by thermal effect due to the Joule heat. Our results show the great potential of the SSL contacts to be used as SECs, such as micro- or nanocontact switches, conductive slip rings, or pantographs.

The stochastic exploration of the configuration space and the exploitation of functional states underlie many biological processes. The evolutionary dynamics stands out as a remarkable example. Here, we introduce a novel formalism that mimics evolution and encodes a general exploration-exploitation dynamics for biological networks. We apply it to the brain wiring problem, focusing on the maturation of that of the nematode Caenorhabditis elegans. We demonstrate that a parsimonious maxent description of the adult brain combined with our framework is able to track down the entire developmental trajectory.

Understanding nanoscale mechanisms responsible for the recently discovered ferroelectric nematics can be helped by direct visualization of self-assembly of strongly polar molecules. Here, we report on scanning tunneling microscopy studies of monomolecular layers of a ferroelectric nematic liquid crystal on a reconstructed Au(111) surface. The monolayers are obtained by deposition from a solution at ambient conditions. The adsorbed ferroelectric nematic molecules self-assemble into regular rows with tilted orientation, resembling a layered structure of a smectic C. Remarkably, each molecular dipole in this architecture is oriented along the same direction giving rise to polar ferroelectric ordering.

We experimentally investigate the statistics of zero-height isolines in gravity wave turbulence as physical candidates for conformal invariant curves. We present direct evidence that they can be described by the family of conformal invariant curves called stochastic Schramm-Löwner evolution (or ${\mathrm{SLE}}_{\kappa }$), with diffusivity $\kappa =2.88(8)$. A higher nonlinearity in the height fields is shown destroy this symmetry, though scale invariance is retained.

Calculating perturbation response properties of materials from first principles provides a vital link between theory and experiment, but is bottlenecked by the high computational cost. Here, a general framework is proposed to perform density functional perturbation theory (DFPT) calculations by neural networks, greatly improving the computational efficiency. Automatic differentiation is applied on neural networks, facilitating accurate computation of derivatives. High efficiency and good accuracy of the approach are demonstrated by studying electron-phonon coupling and related physical quantities. This work brings deep-learning density functional theory and DFPT into a unified framework, creating opportunities for developing ab initio artificial intelligence.

The structure and decay of the most neutron-rich beryllium isotope, ${}^{16}\mathrm{Be}$, has been investigated following proton knockout from a high-energy ${}^{17}\mathrm{B}$ beam. Two relatively narrow resonances were observed for the first time, with energies of 0.84(3) and 2.15(5) MeV above the two-neutron decay threshold and widths of 0.32(8) and 0.95(15) MeV, respectively. These were assigned to be the ground ($J^{\pi }=0^{+}$) and first excited ($2^{+}$) state, with $E_x=1.31(6)\mathrm{MeV}$. The mass excess of ${}^{16}\mathrm{Be}$ was thus deduced to be 56.93(13) MeV, some 0.5 MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wave function during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the $2^{+}$ level presents a far more diffuse neutron-neutron distribution.

We report direct atomic force microscopy measurements of pinning-depinning dynamics of a circular moving contact line (CL) over the rough surface of a micron-sized vertical hanging glass fiber, which intersects a liquid-air interface. The measured capillary force acting on the CL exhibits sawtoothlike fluctuations, with a linear accumulation of force of slope $k$ (stick) followed by a sharp release of force $\delta f$, which is proportional to the CL slip length. From a thorough analysis of a large volume of the stick-slip events, we find that the local maximal force $F_c$ needed for CL depinning follows the extreme value statistics and the measured $\delta f$ follows the avalanche dynamics with a power law distribution in good agreement with the Alessandro-Beatrice-Bertotti-Montorsi (ABBM) model. The experiment provides an accurate statistical description of the CL dynamics at mesoscale, which has important implications to a common class of problems involving stick-slip motion in a random defect or roughness landscape.

A one-dimensional Bose-Hubbard model with unidirectional hopping is shown to be exactly solvable. Applying the algebraic Bethe ansatz method, we prove the integrability of the model and derive the Bethe ansatz equations. The exact eigenvalue spectrum can be obtained by solving these equations. The distribution of Bethe roots reveals the presence of a superfluid-Mott insulator transition at the ground state, and the critical point is determined. By adjusting the boundary parameter, we demonstrate the existence of a non-Hermitian skin effect even in the presence of interaction, but it is completely suppressed for the Mott insulator state in the thermodynamical limit. Our result represents a new class of exactly solvable non-Hermitian many-body systems, which has no Hermitian correspondence and can be used as a benchmark for various numerical techniques developed for non-Hermitian many-body systems.

We study the dynamics of micron-sized particles on a layer of motile cells. This cell carpet acts as an active bath that propels passive tracer particles via direct mechanical contact. The resulting nonequilibrium transport shows a crossover from superdiffusive to normal-diffusive dynamics. The particle displacement distribution is distinctly non-Gaussian even at macroscopic timescales exceeding the measurement time. We obtain the distribution of diffusion coefficients from the experimental data and introduce a model for the displacement distribution that matches the experimentally observed non-Gaussian statistics. We argue why similar transport properties are expected for many composite active matter systems.