We report a surface instability observed during the extrusion of extremely soft elastic solids in confined geometries. Because of their unique rheological properties, these soft solids can migrate through narrow gaps by continuously everting the bulk material. The extrusion front spontaneously buckles in the direction transverse to the flow, resulting in a furrowlike morphology that deepens over time. We characterize the distinct features of this instability using experiments and theory and contrast the results with known elastic surface instabilities. Our Letter may provide insights into various processes involving the extrusionlike deformations of soft solids, including biomaterials.

We study Polchinski’s “fermion-rotor system” as an accurate description of charged Weyl fermions scattering on a magnetic monopole core in the limit of zero gauge coupling. Traditionally it was thought such scattering could lead to fractional particle numbers (“semitons”). By direct calculations we show those semitonic processes are in fact free propagation, facilitated by composite fermion-rotor operators interpolating the “forbidden” states, effectively “recovering” both ingoing and outgoing states in every lowest partial wave. Nonsemitonic Callan-Rubakov processes are unchanged.

We present results over an 11-year Solar cycle of cosmic antiprotons based on $1.1\times {10}^6$ events in the rigidity range from 1.00 to 41.9 GV. The $\overline{p}$ fluxes exhibit distinct properties. The magnitude of the $\overline{p}$ flux temporal variation is significantly smaller than those of $p$, $e^{-}$, and $e^{+}$. A hysteresis between the $\overline{p}$ fluxes and the $p$ fluxes is observed, whereas the $\overline{p}$ and $e^{-}$ fluxes show a linear correlation. With a model-independent analysis, we found a universal relation between the shape of the rigidity spectrum and the magnitude of flux temporal variation over an 11-year Solar cycle for both positively and negatively charged particles. The simultaneous results on $\overline{p}$ and $p$, $e^{-}$, and $e^{+}$ provide unique information for understanding particle transport in the Solar System as a function of mass, charge, and spectral shape.

We study Anderson transition for light in three dimensions by performing large-scale simulations of electromagnetic wave transport in disordered ensembles of perfect-electric-conducting spatially overlapping spheres. A mobility edge that separates diffusive transport and Anderson localization is identified, revealing a sharp transition from diffusion to localization for light. Critical behavior in the vicinity of the mobility edge is well described by a single-parameter scaling law. The critical exponent is found to be consistent with the value known for the Anderson transition of the orthogonal universality class. Statistical distribution of total transmission at the mobility edge is described without any fit parameter by the diagrammatic perturbation theory originally developed for scalar wave diffusion, but notable deviation from the theory is found when Anderson localization sets in.

Spontaneous symmetry breaking can persist at all temperatures in certain biconical $\mathrm{O}(N)\times {\mathbb{Z}}_2$ vector models when the underlying field theories are ultraviolet complete. So far, the existence of such theories has been established in fractional dimensions for local but nonunitary models or in $2+1$ dimensions but for nonlocal models. Here, we study local models at zero and finite temperature directly in $2+1$ dimensions employing functional methods. At zero temperature, we establish that our approach describes the quantum critical behavior with good accuracy for all $N\ge 2$. We then exhibit the mechanism of discrete symmetry breaking from $\mathrm{O}(N)\times {\mathbb{Z}}_2\to \mathrm{O}(N)$ for increasing temperature near the biconical critical point when $N$ is finite but large. We calculate the corresponding finite-temperature phase diagram and further show that the Hohenberg-Mermin-Wagner theorem is fully respected within this approach, i.e., symmetry breaking only occurs in the ${\mathbb{Z}}_2$ sector. Finally, we determine the critical $N$ above which this phenomenon can be observed to be $N_c\approx 15$.

We demonstrate fully quantitative Thiele model simulations of magnetic skyrmion dynamics on previously unattainable experimentally relevant large length and time scales by ascertaining the key missing parameters needed to calibrate the experimental and simulation timescales and current-induced forces. Our work allows us to determine complete spatial pinning energy landscapes that enable quantification of experimental studies of diffusion in arbitrary potentials within the Lifson-Jackson framework. Our method enables us to ascertain the timescales, and by isolating the effect of ultralow current density (order ${10}^6\mathrm{A}/{\mathrm{m}}^2$) generated torques we directly infer the total force acting on the skyrmion for a quantitative modeling.

We demonstrate an optical clock based on Ramsey-Bordé interferometry in a laser-cooled ${}^{40}\mathrm{Ca}$ beam. The mean velocity is reduced by an order of magnitude relative to a thermal beam and the transverse temperature approaches the Doppler limit, enabling the measurement of sub-kHz linewidth fringes in a compact interferometer. Using tailored phase and intensity modulation of the spectroscopy laser to add uniform frequency sidebands, we interrogate atoms throughout the transverse velocity distribution, increasing the Ramsey-Bordé fringe amplitude by a factor of 14 and improving the Allan deviation to $3.4\times {10}^{-15}$ at one second averaging time.

A mirror twin boundary (MTB) in a transition metal dichalcogenide monolayer can host one-dimensional electron liquid of a topological nature with tunable interactions. Unfortunately, electrical characterization of such boundaries has been challenging due to the paucity of samples with large enough size and high quality. Here, we report the conductance measurements of individual MTBs in epitaxially grown monolayer molybdenum disulfide bicrystals that are tens of micrometers long. These MTBs exhibit power-law behaviors of conductance as a function of temperature and bias voltage up to room temperature, consistent with electrons tunneling into a Luttinger liquid. Transport measurements of two distinct types of MTBs reveal the critical role of the atomic-scale defects. This study demonstrates that MTBs in transition metal dichalcogenide monolayers provide an exciting new platform for studying the interplay between electronic interactions and topology.

We report the valence-to-core resonant inelastic x-ray scattering of EuS measured at the ${\mathrm{L}}_3$ edge of Eu. The obtained data reveal two sets of excitations: one set is composed of a hole in the S 3p bands and an electron excited to extended Eu 5d band states, and the other is made up from a hole in the Eu 4f states and an electron in localized Eu 5d states bound to the 4f hole by its Coulomb potential. The delocalized excitations arise from the dipole-allowed $5\mathrm{d}\to 2\mathrm{p}$ emissions, whereas the localized excitations result from the dipole-forbidden (quadrupole-allowed) $4\mathrm{f}\to 2\mathrm{p}$ emissions. Both these emission channels have a comparable intensity thanks to a small number of occupied 5d states ($\approx 0.6$) combined with a large number of occupied 4f states (seven). We identify the localized electron-hole pairs with the “magnetic excitons” suggested in the past as an interpretation of the sharp features seen in the optical absorption spectra. Our observations provide a direct experimental evidence of these excitons, which has been missing up to now.

Excitonic effects in metals are usually supposed to be weak, because the Coulomb interaction is strongly screened. Here, we investigate the low-density regime of the homogeneous electron gas, where, besides the usual high-energy plasmons, the existence of low-energy excitonic collective modes has recently been suggested. Using the Bethe-Salpeter equation (BSE), we show that indeed low-energy modes appear, thanks to reduced screening at short distances. This requires going beyond common approximations to ab initio BSE calculations, which suffer from a self-polarization error that overscreens the electron-hole interaction. The electron-hole wave function of the low-energy mode shows strong and very anisotropic electron-hole correlation, which speaks for an excitonic character of this mode. The fact that the electron-hole interaction at short distances is at the origin of these phenomena explains why, on the other hand, also the simple adiabatic local density approximation to time-dependent density functional theory can capture these effects. This exotic regime might be found in doped semiconductors and interfaces.

Although real-world complex systems typically interact through sparse and heterogeneous networks, analytic solutions of their dynamics are limited to models with all-to-all interactions. Here, we solve the dynamics of a broad range of nonlinear models of complex systems on sparse directed networks with a random structure. By generalizing dynamical mean-field theory to sparse systems, we derive an exact equation for the path probability describing the effective dynamics of a single degree of freedom. Our general solution applies to key models in the study of neural networks, ecosystems, epidemic spreading, and synchronization. Using the population dynamics algorithm, we solve the path-probability equation to determine the phase diagram of a seminal neural network model in the sparse regime, showing that this model undergoes a transition from a fixed-point phase to chaos as a function of the network topology.

We solve a model of electrons with Hubbard-$U$ Coulomb repulsion and a random Yukawa coupling to a two-dimensional bosonic bath, using an extended dynamical mean field theory scheme. Our model exhibits a quantum critical point, at which the repulsive component of the electron interactions strongly enhances the effects of the quantum critical bosonic fluctuations on the electrons, leading to a breakdown of Fermi liquid physics and the formation of a strange metal with “Planckian” [$\mathcal{O}(k_{B}T/\hslash )$] quasiparticle decay rates at low temperatures $T\to 0$. Furthermore, the eventual Mott transition that occurs as the repulsion is increased seemingly bounds the maximum decay rate in the strange metal. Our results provide insight into low-temperature strange metallicity observed in proximity to a Mott transition, as is observed, for instance, in recent experiments on certain moiré materials.

Structure-dynamics correlation is one of the major ongoing debates in the glass transition, although a number of structural features have been found connected to the dynamic heterogeneity in different glass-forming colloidal systems. Here, using colloidal experiments combined with coarse-grained molecular dynamics simulations, we investigate the glass transition in monolayers of rough colloidal ellipsoids. Compared with smooth colloidal ellipsoids, the surface roughness of ellipsoids is found to significantly change the nature of glass transition. In particular, we find that the surface roughness induced by coating only a few small hemispheres on the ellipsoids can eliminate the existence of orientational glass and the two-step glass transition found in monolayers of smooth ellipsoids. This is due to the surface roughness-induced coupling between the translational and rotational degrees of freedom in colloidal ellipsoids, which also destroys the structure-dynamics correlation found in glass-forming suspensions of colloidal ellipsoids. Our results not only suggest a new way of using surface roughness to manipulate the glass transition in colloidal systems, but also highlight the importance of detailed particle shape on the glass transition and structure-dynamics correlation in suspensions of anisotropic colloids.

We discover unexpected connections between packing configurations and rare fluctuations in dense systems of active particles subject to pulsation of size. Using large deviation theory, we examine biased ensembles which select atypical realizations of the dynamics exhibiting high synchronization in particle size. We show that the order emerging at high bias can manifest as distinct dynamical states featuring high to vanishing pulsation current. Remarkably, transitions between these states arise from changing the system geometry at fixed bias and constant density. We rationalize such transitions as arising from the change in packing configurations which, depending on box geometry, may induce highly ordered or geometrically frustrated structures. Furthermore, we reveal that a master curve in the unbiased dynamics, correlating polydispersity and current, helps predict the dynamical state emerging in the biased dynamics. Finally, we demonstrate that deformation waves can propagate under suitable geometries when biasing with local order.

Pulsar timing arrays (PTAs) detect gravitational waves (GWs) via the correlations they create in the arrival times of pulses from different pulsars. The mean correlation, a function of the angle between the directions to two pulsars, was predicted in 1983 by Hellings and Downs (HD). Observation of this angular pattern is crucial evidence that GWs are present, so PTAs “reconstruct the HD curve” by estimating the correlation using pulsar pairs separated by similar angles. Several studies have examined the amount by which this curve is expected to differ from the HD mean. The variance arises because (a) a finite set of pulsars at specific sky locations is used, (b) the GW sources interfere, and (c) the data are contaminated by noise. Here, for a Gaussian ensemble of sources, we predict that variance by constructing an optimal estimator of the HD correlation, taking into account the pulsar sky locations and the frequency distribution of the GWs and the pulsar noise. The variance is a ratio: the numerator depends upon the pulsar sky locations, and the denominator is the (effective) number of frequency bins for which the GW signal dominates the noise. In effect, after suitable combination, each such frequency bin gives an independent estimate of the HD correlation.

Discriminating the effects of different kinds of scattering in strongly interacting metals is crucial in their understanding. While momentum or current relaxation can be readily probed via dc resistivity or linear terahertz (THz) spectroscopy, discriminating other kinds of scattering can be more challenging. In this Letter, we argue that the nonlinear optical technique of THz 2D coherent spectroscopy measures the energy relaxation rate in strongly interacting metals. We apply the technique to the Fermi liquid ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ and observe two energy relaxation channels: a fast process ($\sim 0.1\mathrm{THz}$) that we interpret as energy loss to the phonon system and a much slower relaxation ($\lesssim 1\mathrm{GHz}$) that we interpret as the relaxation of nonequilibrium phonons. Both rates are at least an order of magnitude slower than the momentum relaxation rate. We show how energy relaxation provides a unique diagnostic into certain kinds of scattering and among other aspects allows a measure of the dimensionless electron-phonon coupling constant. Our observations reveal the versatility of nonlinear THz spectroscopy to measure the energy relaxation dynamics in correlated metals and also highlights the need for improved theoretical understanding of such processes in interacting metals.

We present a first experimental study of dark current in a quanta image sensor (QIS) based on complementary metal-oxide-semiconductor (CMOS) technology. With the extremely low noise levels of this sensor it is possible to observe spatial and temporal dark current quantization. Analysis of dark carrier emission timing confirms that carrier generation behaves as a Poisson process. The mean of this Poisson distribution is the only parameter needed to characterize a sensor, thus greatly reducing the required measurement and computational resources typically employed in device noise analysis. The impact of this new characterization method will be useful to a range of industrial and scientific applications requiring high accuracy in photoelectron counting, such as in particle detection or quantum sensing. The ability to observe single carrier emission in a QIS leads to a deeper understanding of the mechanism of dark current generation in state-of-the-art semiconductors, thereby promoting improvements in the development of device design and process technology.

It has been proposed recently that the breaking of magnetohydrodynamics (MHD) waves in the inner magnetosphere of strongly magnetized neutron stars can power different types of high-energy transients. Motivated by these considerations, we study the steepening and dissipation of a strongly magnetized fast magnetosonic wave propagating in a declining background magnetic field, by means of particle-in-cell simulations that encompass MHD scales. Our analysis confirms the formation of a monster shock as $B^2-E^2\to 0$, that dissipates about half of the fast magnetosonic wave energy. It also reveals, for the first time, the generation of a high-frequency precursor wave by the monster shock, carrying a fraction of $\sim {10}^{-3}$ of the total energy dissipated at the shock. The spectrum of the precursor wave exhibits several sharp harmonic peaks, with frequencies in the gigahertz band under conditions anticipated in magnetars. Such signals may appear as fast radio bursts.

We demonstrate a switchable electron shell structure in a bilayer graphene quantum dot by manipulating the trigonal warping effect upon electrical gating. Under a small perpendicular electric field, the lowest $s$ shell is sequentially filled with two spin-up and two spin-down electrons of opposite valleys. When increasing the electric field, an additional threefold minivalley degeneracy is generated so that the $s$ shell can be filled with 12 electrons with the first (last) six electrons having the same spin polarization. The switched spin filling sequence demonstrates the possibility of using the trigonal warping effect to electrically access and manipulate the spin degree of freedom in bilayer graphene.

Memory effects are ubiquitous in small-scale systems. They emerge from interactions between accessible and inaccessible degrees of freedom and give rise to evolution equations that are nonlocal in time. If the characteristic timescales of accessible and inaccessible degrees of freedom are sharply separated, locality can be restored through the standard Markov approximation. Here, we show that this approach can be rigorously extended to a well-defined weak-memory regime, where the relevant timescales can be of comparable order of magnitude. We derive explicit bounds on the error of the local approximation and a convergent perturbation scheme for its construction. Being applicable to any nonlocal time evolution equation that is autonomous and linear in the variables of interest, our theory provides a unifying framework for the systematic description of memory effects.