A key aspect of unconventional pairing by the antiferromagnetic spin-fluctuation mechanism is that the superconducting energy gap must have the opposite sign on different parts of the Fermi surface. Recent observations of non-nodal gap structure in the heavy-fermion superconductor ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ were then very surprising, given that this material has long been considered a prototypical example of a superconductor where the Cooper pairing is magnetically mediated. Here we present a study of the effect of controlled point defects, introduced by electron irradiation, on the temperature-dependent magnetic penetration depth $\lambda (T)$ in ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$. We find that the fully gapped state is robust against disorder, demonstrating that low-energy bound states, expected for sign-changing gap structures, are not induced by nonmagnetic impurities. This provides bulk evidence for $s_{++}$-wave superconductivity without sign reversal.

The spin and parity of the $Z_c(3900{)}^{\pm }$ state are determined to be $J^P=1^{+}$ with a statistical significance larger than $7\sigma$ over other quantum numbers in a partial wave analysis of the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$. We use a data sample of $1.92{\mathrm{fb}}^{-1}$ accumulated at $\sqrt{s}=4.23$ and 4.26 GeV with the BESIII experiment. When parametrizing the $Z_c(3900{)}^{\pm }$ with a Flatté-like formula, we determine its pole mass $M_{\text{pole}}=(3881.2\pm 4.2_{\text{stat}}\pm 52.7_{\text{syst}})\mathrm{MeV}/c^2$ and pole width ${\mathrm{\Gamma }}_{\text{pole}}=(51.8\pm {4.6}_{\text{stat}}\pm {36.0}_{\text{syst}})\mathrm{MeV}$. We also measure cross sections for the process $e^{+}{e}^{-}\to Z_c(3900{)}^{+}{\pi }^{-}+\mathrm{c}.\mathrm{c}.\to J/\psi {\pi }^{+}{\pi }^{-}$ and determine an upper limit at the 90% confidence level for the process $e^{+}{e}^{-}\to Z_c(4020{)}^{+}{\pi }^{-}+\mathrm{c}.\mathrm{c}.\to J/\psi {\pi }^{+}{\pi }^{-}$.

High $P\text{−}T$ Raman spectra of hydrogen in the vibron and lattice mode regions were measured up to 300 GPa and 900 K using externally heated diamond anvil cell techniques. A new melting line determined from the disappearance of lattice mode excitations was measured directly for the first time above 140 GPa. The results differ from theoretical predictions and extrapolations from lower pressure melting relations. In addition, discontinuities in Raman frequencies are observed as a function of pressure and temperature indicative of phase transition at these conditions. The appearance of a new Raman feature near $2700{\mathrm{cm}}^{-1}$ at $\sim 300\mathrm{GPa}$ and 370 K indicates the transformation to a new crystalline phase. Theoretical calculations of the spectrum suggest the new phase is the proposed $Cmca\text{−}4$ metallic phase. The transition pressure is close to that of a recently reported transition observed on dynamic compression.

We demonstrate the generation of alternating spin current (SC) via spin-rotation coupling (SRC) using a surface acoustic wave (SAW) in a Cu film. Ferromagnetic resonance caused by injecting SAWs was observed in a Ni-Fe film attached to a Cu film, with the resonance further found to be suppressed through the insertion of a ${\mathrm{SiO}}_2$ film into the interface. The intensity of the resonance depended on the angle between the wave vector of the SAW and the magnetization of the Ni-Fe film. This angular dependence is explicable in terms of the presence of spin transfer torque from a SC generated via SRC.

We report on combined measurements of heat and charge transport through a single-electron transistor. The device acts as a heat switch actuated by the voltage applied on the gate. The Wiedemann-Franz law for the ratio of heat and charge conductances is found to be systematically violated away from the charge degeneracy points. The observed deviation agrees well with the theoretical expectation. With a large temperature drop between the source and drain, the heat current away from degeneracy deviates from the standard quadratic dependence in the two temperatures.

We apply near-threshold laser photodetachment to characterize the rotational quantum level distribution of ${\mathrm{OH}}^{-}$ ions stored in the cryogenic ion-beam storage ring DESIREE at Stockholm University. We find that the stored ions relax to a rotational temperature of $13.4\pm 0.2\mathrm{K}$ with $94.9\pm 0.3\%$ of the ions in the rotational ground state. This is consistent with the storage ring temperature of $13.5\pm 0.5\mathrm{K}$ as measured with eight silicon diodes but in contrast to all earlier studies in cryogenic traps and rings where the rotational temperatures were always much higher than those of the storage devices at their lowest temperatures. Furthermore, we actively modify the rotational distribution through selective photodetachment to produce an ${\mathrm{OH}}^{-}$ beam where $99.1\pm 0.1\%$ of approximately one million stored ions are in the $J=0$ rotational ground state. We measure the intrinsic lifetime of the $J=1$ rotational level to be $145\pm 28\mathrm{s}$.

By means of extensive lattice-element simulations, we investigate stress transmission and its relation with failure properties in increasingly disordered porous systems. We observe a non-Gaussian broadening of stress probability density functions under tensile loading with increasing porosity and disorder, revealing a gradual transition from a state governed by single-pore stress concentration to a state controlled by multipore interactions and metric disorder. This effect is captured by the excess kurtosis of stress distributions and shown to be nicely correlated with the second moment of local porosity fluctuations, which appears thus as a (dis)order parameter for the system. By generating statistical ensembles of porous textures with varying porosity and disorder, we derive a general expression for the fracture stress as a decreasing function of porosity and disorder. Focusing on critical sites where the local stress is above the global fracture threshold, we also analyze the transition to failure in terms of a coarse-graining length. These findings provide a general framework which can also be more generally applied to multiphase and structural heterogeneous materials.

The nuclear matrix element determining the $pp\to d{e}^{+}\nu$ fusion cross section and the Gamow-Teller matrix element contributing to tritium $\beta$ decay are calculated with lattice quantum chromodynamics for the first time. Using a new implementation of the background field method, these quantities are calculated at the SU(3) flavor–symmetric value of the quark masses, corresponding to a pion mass of $m_{\pi }\sim 806\mathrm{MeV}$. The Gamow-Teller matrix element in tritium is found to be 0.979(03)(10) at these quark masses, which is within $2\sigma$ of the experimental value. Assuming that the short-distance correlated two-nucleon contributions to the matrix element (meson-exchange currents) depend only mildly on the quark masses, as seen for the analogous magnetic interactions, the calculated $pp\to d{e}^{+}\nu$ transition matrix element leads to a fusion cross section at the physical quark masses that is consistent with its currently accepted value. Moreover, the leading two-nucleon axial counterterm of pionless effective field theory is determined to be $L_{1,A}=3.9(0.2)(1.0)(0.4)(0.9){\mathrm{fm}}^3$ at a renormalization scale set by the physical pion mass, also agreeing within the accepted phenomenological range. This work concretely demonstrates that weak transition amplitudes in few-nucleon systems can be studied directly from the fundamental quark and gluon degrees of freedom and opens the way for subsequent investigations of many important quantities in nuclear physics.

We report the first dijet transverse momentum asymmetry measurements from $\mathrm{Au}+\mathrm{Au}$ and $pp$ collisions at RHIC. The two highest-energy back-to-back jets reconstructed from fragments with transverse momenta above $2\mathrm{GeV}/c$ display a significantly higher momentum imbalance in heavy-ion collisions than in the $pp$ reference. When reexamined with correlated soft particles included, we observe that these dijets then exhibit a unique new feature—momentum balance is restored to that observed in $pp$ for a jet resolution parameter of $R=0.4$, while rebalancing is not attained with a smaller value of $R=0.2$.

Graded metasurfaces exploit the local momentum imparted by an impedance gradient to mold the impinging wave front. This approach suffers from fundamental limits on the overall conversion efficiency, and it is challenged by fabrication limitations on the spatial resolution. Here, we introduce the concept of metagratings, formed by periodic arrays of carefully tailored bianisotropic inclusions and show that they enable wave front engineering with unitary efficiency and significantly lower fabrication demands. We employ this concept to design reflective metasurfaces for wave front steering without limitations on efficiency. A similar approach can be extended to transmitted beams and arbitrary wave front transformation, opening opportunities for highly efficient metasurfaces for extreme wave manipulation.

We show that a high-energy electron bunch can be used to capture the instantaneous longitudinal and transverse field structures of the highly transient, microscopic, laser-excited relativistic wake with femtosecond resolution. The spatiotemporal evolution of wakefields in a plasma density up ramp is measured and the reversal of the plasma wake, where the wake wavelength at a particular point in space increases until the wake disappears completely only to reappear at a later time but propagating in the opposite direction, is observed for the first time by using this new technique.

We report an x-ray photon correlation spectroscopy method that exploits the recent development of the two-pulse mode at the Linac Coherent Light Source. By using coherent resonant x-ray magnetic scattering, we studied spontaneous fluctuations on nanosecond time scales in thin films of multilayered Fe/Gd that exhibit ordered stripe and Skyrmion lattice phases. The correlation time of the fluctuations was found to differ between the Skyrmion phase and near the stripe-Skyrmion boundary. This technique will enable a significant new area of research on the study of equilibrium fluctuations in condensed matter.

We propose that the dark matter abundance is set by the decoupling of inelastic scattering instead of annihilations. This coscattering mechanism is generically realized if dark matter scatters against states of comparable mass from the thermal bath. Coscattering points to dark matter that is exponentially lighter than the weak scale and has a suppressed annihilation rate, avoiding stringent constraints from indirect detection. Dark matter upscatters into states whose late decays can lead to observable distortions to the blackbody spectrum of the cosmic microwave background.

The precise value of the $g$ factor in graphene is of fundamental interest for all spin-related properties and their application. We investigate monolayer graphene on a $\mathrm{Si}/{\mathrm{SiO}}_2$ substrate by resistively detected electron spin resonance. Surprisingly, the magnetic moment and corresponding $g$ factor of $1.952\pm 0.002$ is insensitive to charge carrier type, concentration, and mobility.

We show that some or all of the inventory of $r$-process nucleosynthesis can be produced in interactions of primordial black holes (PBHs) with neutron stars (NSs) if PBHs with masses ${10}^{-14}{M}_{\odot }<M_{\mathrm{PBH}}<{10}^{-8}{M}_{\odot }$ make up a few percent or more of dark matter. A PBH captured by a NS sinks to the center of the NS and consumes it from the inside. When this occurs in a rotating millisecond-period NS, the resulting spin-up ejects $\sim 0.1M_{\odot }–0.5M_{\odot }$ of relatively cold neutron-rich material. This ejection process and the accompanying decompression and decay of nuclear matter can produce electromagnetic transients, such as a kilonova-type afterglow and fast radio bursts. These transients are not accompanied by significant gravitational radiation or neutrinos, allowing such events to be differentiated from compact object mergers occurring within the distance sensitivity limits of gravitational-wave observatories. The PBH-NS destruction scenario is consistent with pulsar and NS statistics, the dark-matter content, and spatial distributions in the Galaxy and ultrafaint dwarfs, as well as with the $r$-process content and evolution histories in these sites. Ejected matter is heated by beta decay, which leads to emission of positrons in an amount consistent with the observed 511-keV line from the Galactic center.

A freestanding molecular wire is placed vertically on Au(111) using a platform molecule and contacted by a scanning tunneling microscope. Despite the simplicity of the single-molecule junction, its conductance $G$ reproducibly varies in a complex manner with the electrode separation. Transport calculations show that $G$ is controlled by a deformation of the molecule, a symmetry mismatch between the tip and molecule orbitals, and the breaking of a $\mathrm{C}\equiv \mathrm{C}$ triple in favor of a $\mathrm{Au}─\mathrm{C}─\mathrm{C}$ bond. This tip-controlled reversible bond formation or rupture alters the electronic spectrum of the junction and the states accessible for transport, resulting in an order of magnitude variation of the conductance.

A search for the dimuon decay of the Higgs boson was performed using data corresponding to an integrated luminosity of $36.1{\mathrm{fb}}^{-1}$ collected with the ATLAS detector in $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$ at the Large Hadron Collider. No significant excess is observed above the expected background. The observed (expected) upper limit on the cross section times branching ratio is 3.0 (3.1) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125 GeV. When combined with the $pp$ collision data at $\sqrt{s}=7\mathrm{TeV}$ and $\sqrt{s}=8\mathrm{TeV}$, the observed (expected) upper limit is 2.8 (2.9) times the Standard Model prediction.

The direct photodissociation of ${\mathrm{D}}_2$ at excitation energies above 14.76 eV occurs via two channels, $\mathrm{D}(2s)+\mathrm{D}(1s)$ and $\mathrm{D}(2p)+\mathrm{D}(1s)$. The branching ratios between the two have been measured from the dissociation threshold to $3200{\mathrm{cm}}^{-1}$ above it, and it is found that they show cosine oscillations as a function of the fragment wave vector magnitudes. The oscillation is due to an interference effect and can be simulated using the phase difference between the wave functions of the two channels, analogous to Young’s double-slit experiment. By fitting the measured branching ratios, we have determined the depths and widths of the effective spherical potential wells related to the two channels, which are in agreement with the effective depths and widths of the ab initio interaction potentials. The results of this Letter illustrate the importance of the relative phase between the fragments in controlling the branching ratios of the photodissociation channels.

It is commonly thought that biological media cannot exhibit an appreciable nonlinear optical response. We demonstrate, for the first time to our knowledge, a tunable optical nonlinearity in suspensions of cyanobacteria that leads to robust propagation and strong self-action of a light beam. By deliberately altering the host environment of the marine bacteria, we show experimentally that nonlinear interaction can result in either deep penetration or enhanced scattering of light through the bacterial suspension, while the viability of the cells remains intact. A theoretical model is developed to show that a nonlocal nonlinearity mediated by optical forces (including both gradient and forward-scattering forces) acting on the bacteria explains our experimental observations.

We investigate the sliding of objects on an inclined granular surface close to the avalanche threshold. Our experiments show that the stability is driven by the surface deformations. Heavy objects generate footprintlike deformations which stabilize the objects on the slopes. Light objects do not disturb the sandy surfaces and are also stable. For intermediate weights, the deformations of the surface generate a sliding of the objects. The solid friction coefficient does not follow the Amontons-Coulomb laws, but is found minimal for a characteristic pressure. Applications to the locomotion of devices and animals on sandy slopes as a function of their mass are proposed.