We report a new way to strongly couple graphene to a superconductor. The graphene monolayer has been grown directly on top of a superconducting Re(0001) thin film and characterized by scanning tunneling microscopy and spectroscopy. We observed a moiré pattern due to the mismatch between Re and graphene lattice parameters that we have simulated with ab initio calculations. The density of states around the Fermi energy appears to be position dependent on this moiré pattern. Tunneling spectroscopy performed at 50 mK shows that the superconducting behavior of graphene on Re is well described by the Bardeen-Cooper-Schrieffer theory and stands for a very good interface between the graphene and its metallic substrate.

It is widely believed that the mechanism for spin pumping in ferromagnet-nonmagnet bilayers is the exchange interaction between the ferromagnet and nonmagnetic material. We observe 1000-fold exponential decay of spin pumping from thin ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ films to Pt across insulating barriers, from which exponential decay lengths of 0.16, 0.19, and 0.23 nm are extracted for oxide barriers having band gaps of 4.91, 3.40, and 2.36 eV, respectively. This archetypal signature of quantum tunneling through a barrier underscores the importance of exchange coupling for spin pumping and reveals its dependence on the characteristics of the barrier material.

We report a strong effect of interface-induced magnetization on the transport properties of magnetic tunnel junctions consisting of ferromagnetic manganite ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ and insulating cuprate ${\mathrm{PrBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$. Contrary to the typically observed steady increase of the tunnel magnetoresistance with decreasing temperature, this system exhibits a sudden anomalous decrease at low temperatures. Interestingly, this anomalous behavior can be attributed to the competition between the positive spin polarization of the manganite contacts and the negative spin-filter effect from the interface-induced Cu magnetization.

We show that it is possible to realize significant nonlinear optical interactions at the few photon level in graphene nanostructures. Our approach takes advantage of the electric field enhancement associated with the strong confinement of graphene plasmons and the large intrinsic nonlinearity of graphene. Such a system could provide a powerful platform for quantum nonlinear optical control of light. As an example, we consider an integrated optical device that exploits this large nonlinearity to realize a single photon switch.

Resonant piezoelectric spectroscopy shows polar resonances in paraelectric ${\mathrm{SrTiO}}_3$ at temperatures below 80 K. These resonances become strong at $T<40\mathrm{K}$. The resonances are induced by weak electric fields and lead to standing mechanical waves in the sample. This piezoelectric response does not exist in paraelastic ${\mathrm{SrTiO}}_3$ nor at temperatures just below the ferroelastic phase transition. The interpretation of the resonances is related to ferroelastic twin walls which become polar at low temperatures in close analogy with the known behavior of ${\mathrm{CaTiO}}_3$. ${\mathrm{SrTiO}}_3$ is different from ${\mathrm{CaTiO}}_3$, however, because the wall polarity is thermally induced; i.e., there exists a small temperature range well below the ferroelastic transition point at 105 K where polarity appears on cooling. As the walls are atomistically thin, this transition has the hallmarks of a two-dimensional phase transition restrained to the twin boundaries rather than a classic bulk phase transition.

The gliding motility of Flavobacterium johnsoniae is driven by moving surface adhesive proteins. Recently, these motility components were observed to travel along a closed loop on the cell surface. The mechanism by which such moving surface adhesins give rise to cell motion remains unknown. On the basis of the unique motility properties of F. johnsoniae, we present a generic model for bidirectional motion of rigidly coupled adhesins, which are propelled in opposite directions. Using analytical and numerical methods, we demonstrate that, for a sufficiently large adhesin speed, bidirectional motion arises from spontaneous symmetry breaking. The model also predicts that, close to the bifurcation point, a weak asymmetry in the binding dynamics is sufficient to facilitate directed motility, indicating that the direction of motion could be sensitively regulated internally in response to inhomogeneity of the environment.

We describe theoretically and observe experimentally the formation of a surface state in a semi-infinite waveguide array with a side-coupled waveguide, designed to simultaneously achieve Fano and Fabry-Perot resonances. We demonstrate that the surface mode is compact, with all energy concentrated in a few waveguides at the edge and no field penetration beyond the side-coupled waveguide position. Furthermore, we show that by broadening the spectral band in the rest of the waveguide array it is possible to suppress exponentially localized modes, while the Fano state having the eigenvalue embedded in the continuum is preserved.

Long-lived and high-fidelity memory for a photonic polarization qubit (PPQ) is crucial for constructing quantum networks. We present a millisecond storage system based on electromagnetically induced transparency, in which a moderate magnetic field is applied on a cold-atom cloud to lift Zeeman degeneracy and, thus, the PPQ states are stored as two magnetic-field-insensitive spin waves. Especially, the influence of magnetic-field-sensitive spin waves on the storage performances is almost totally avoided. The measured average fidelities of the polarization states are 98.6% at $200\mu \mathrm{s}$ and 78.4% at 4.5 ms, respectively.

Assuming that the particle with mass $\sim 126\mathrm{GeV}$ discovered at LHC is the standard model Higgs boson, we find that the stability of the electroweak (EW) vacuum strongly depends on new physics interaction at the Planck scale $M_P$, despite of the fact that they are higher-dimensional interactions, apparently suppressed by inverse powers of $M_P$. In particular, for the present experimental values of the top and Higgs boson masses, if $\tau$ is the lifetime of the EW vacuum, new physics can turn $\tau$ from $\tau \gg T_U$ to $\tau \ll T_U$, where $T_U$ is the age of the Universe, thus, weakening the conclusions of the so called metastability scenario.

We study $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{h}_c$ at center-of-mass energies from 3.90 to 4.42 GeV by using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections are measured at 13 energies and are found to be of the same order of magnitude as those of $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ but with a different line shape. In the ${\pi }^{\pm }{h}_c$ mass spectrum, a distinct structure, referred to as $Z_c(4020)$, is observed at $4.02\mathrm{GeV}/c^2$. The $Z_c(4020)$ carries an electric charge and couples to charmonium. A fit to the ${\pi }^{\pm }{h}_c$ invariant mass spectrum, neglecting possible interferences, results in a mass of $(4022.9\pm 0.8\pm 2.7)\mathrm{MeV}/c^2$ and a width of $(7.9\pm 2.7\pm 2.6)\mathrm{MeV}$ for the $Z_c(4020)$, where the first errors are statistical and the second systematic. The difference between the parameters of this structure and the $Z_c(4025)$ observed in the $D^{*}{\overline{D}}^{*}$ final state is within $1.5\sigma$, but whether they are the same state needs further investigation. No significant $Z_c(3900)$ signal is observed, and upper limits on the $Z_c(3900)$ production cross sections in ${\pi }^{\pm }{h}_c$ at center-of-mass energies of 4.23 and 4.26 GeV are set.

The $E1$ strength distribution in ${}^{68}\mathrm{Ni}$ has been investigated using Coulomb excitation in inverse kinematics at the $\mathrm{R}{}^3\mathrm{B}\mathrm{\text{−}}\mathrm{LAND}$ setup and by measuring the invariant mass in the one- and two-neutron decay channels. The giant dipole resonance and a low-lying peak (pygmy dipole resonance) have been observed at 17.1(2) and 9.55(17) MeV, respectively. The measured dipole polarizability is compared to relativistic random phase approximation calculations yielding a neutron-skin thickness of 0.17(2) fm. A method and analysis applicable to neutron-rich nuclei has been developed, allowing for a precise determination of neutron skins in nuclei as a function of neutron excess.

The transient appearance of bright spots in the beam profile of optical filaments formed in xenon is experimentally investigated. Fluence profiles are recorded with high-speed optical cameras at the kilohertz repetition rate of the laser source. A statistical analysis reveals a thresholdlike appearance of heavy-tailed fluence distributions together with the transition from single to multiple filamentation. The multifilament scenario exhibits near-exponential probability density functions, with extreme events exceeding the significant wave height by more than a factor of 10. The extreme events are isolated in space and in time. The macroscopic origin of these experimentally observed heavy-tail statistics is shown to be local refractive index variations inside the nonlinear medium, induced by multiphoton absorption and subsequent plasma thermalization. Microscopically, mergers between filament strings appear to play a decisive role in the observed rogue wave statistics.

We propose a new and simple strategy for controlled ionization-induced trapping of electrons in a beam-driven plasma accelerator. The presented method directly exploits electric wakefields to ionize electrons from a dopant gas and capture them into a well-defined volume of the accelerating and focusing wake phase, leading to high-quality witness bunches. This injection principle is explained by example of three-dimensional particle-in-cell calculations using the code OSIRIS. In these simulations a high-current-density electron-beam driver excites plasma waves in the blowout regime inside a fully ionized hydrogen plasma of density $5\times {10}^{17}{\mathrm{cm}}^{-3}$. Within an embedded $100\mu \mathrm{m}$ long plasma column contaminated with neutral helium gas, the wakefields trigger ionization, trapping of a defined fraction of the released electrons, and subsequent acceleration. The hereby generated electron beam features a 1.5 kA peak current, $1.5\mu \mathrm{m}$ transverse normalized emittance, an uncorrelated energy spread of 0.3% on a GeV-energy scale, and few femtosecond bunch length.

For a spin-carrying particle moving in a spatially varying magnetic field, effective electromagnetic forces can arise due to the geometric phase associated with adiabatic spin rotation of the particle. We report the observation of a geometric Hall effect in a spinor Bose-Einstein condensate with a Skyrmion spin texture. Under translational oscillations of the spin texture, the condensate resonantly develops a circular motion in a harmonic trap, demonstrating the existence of an effective Lorentz force. When the condensate circulates, quantized vortices are nucleated in the boundary region of the condensate and the vortex number increases over 100 without significant heating. We attribute the vortex nucleation to the shearing effect of the effective Lorentz force from the inhomogeneous effective magnetic field.

We present the first use of a waveform-dependent absorbing metasurface for high-power pulsed surface currents. The new type of nonlinear metasurface, composed of circuit elements including diodes, is capable of storing high-power pulse energy to dissipate it between pulses, while allowing propagation of small signals. Interestingly, the absorbing performance varies for high-power pulses but not for high-power continuous waves (CW’s), since the capacitors used are fully charged up. Thus, the waveform dependence enables us to distinguish various signal types (i.e., CW or pulse) even at the same frequency, which potentially creates new kinds of microwave technologies and applications.

Dirac metals (gapless semiconductors) are believed to turn into Weyl metals when perturbations, which break either time reversal symmetry or inversion symmetry, are employed. However, no experimental evidence has been reported for the existence of Weyl fermions in three dimensions. Applying magnetic fields near the topological phase transition from a topological insulator to a band insulator in ${\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x$ we observe not only the weak antilocalization phenomenon in magnetoconductivity near zero magnetic fields ($B<0.4\mathrm{T}$), but also its upturn above 0.4 T only for $E//B$. This “incompatible” coexistence between weak antilocalization and “negative” magnetoresistivity is attributed to the Adler-Bell-Jackiw anomaly (“topological” $E·B$ term) in the presence of weak antilocalization corrections.

The anharmonicity of the potential well confining a magnetic vortex core in a nanodot is measured dynamically with a magnetic resonance force microscope (MRFM). The stray field of the MRFM tip is used to displace the equilibrium core position away from the nanodot center. The anharmonicity is then inferred from the relative frequency shift induced on the eigenfrequency of the vortex core translational mode. An analytical framework is proposed to extract the anharmonic coefficient from this variational approach. Traces of these shifts are recorded while scanning the tip above an isolated nanodot, patterned out of a single crystal FeV film. We observe a $+10\%$ increase of the eigenfrequency when the equilibrium position of the vortex core is displaced to about one-third of its radius. This calibrates the tunability of the gyrotropic mode by external magnetic fields.

Finite-temperature properties of epitaxial films made of $\mathrm{Ba}(\mathrm{Zr},\mathrm{Ti}){\mathrm{O}}_3$ relaxor ferroelectrics are determined as a function of misfit strain, via the use of a first-principles-based effective Hamiltonian. These films are macroscopically paraelectric at any temperature, for any strain ranging between $\simeq -3\%$ and $\simeq +3\%$. However, original temperature-versus-misfit strain phase diagrams are obtained for the Burns temperature ($T_b$) and for the critical temperatures ($T_{m,z}$ and $T_{m,\mathrm{IP}}$) at which the out-of-plane and in-plane dielectric response peak, respectively, which allow the identification of three different regions. These latter differ from their evolution of $T_b$, $T_{m,z}$, and/or $T_{m,\mathrm{IP}}$ with strain, which are the fingerprints of a remarkable strain-induced microscopic change: each of these regions is associated with its own characteristic behavior of polar nanoregions at low temperature, such as strain-induced rotation or strain-driven elongation of their dipoles or even increase in the average size of the polar nanoregions when the strength of the strain grows.

We consider reversible work extraction from identical quantum systems. From an ensemble of individually passive states, work can be produced only via global unitary (and thus entangling) operations. However, we show here that there always exists a method to extract all possible work without creating any entanglement, at the price of generically requiring more operations (i.e., additional time). We then study faster methods to extract work and provide a quantitative relation between the amount of generated multipartite entanglement and extractable work. Our results suggest a general relation between entanglement generation and the power of work extraction.

We present surprising experimental evidence regarding the past of photons passing through an interferometer. The information about the positions through which the photons pass in the interferometer is retrieved from modulations of the detected signal at the vibration frequencies of mirrors the photons bounce off. From the analysis we conclude that the past of the photons is not represented by continuous trajectories, although a “common sense” analysis adopted in various welcher weg measurements, delayed-choice which-path experiments, and counterfactual communication demonstrations yields a single trajectory. The experimental results have a simple explanation in the framework of the two-state vector formalism of quantum theory.