We have imaged a freestanding graphene sheet of 210 nm in diameter with 2 Å resolution by combining coherent diffraction and holography with low-energy electrons. The entire sheet is reconstructed from a single diffraction pattern displaying the arrangement of 660.000 individual graphene unit cells at once. Given the fact that electrons with kinetic energies of the order of 100 eV do not damage biological molecules, it will now be a matter of developing methods for depositing individual proteins onto such graphene sheets.

Recent experimental measurements of Ag impurity diffusion in the $\Sigma 5(310)$ grain boundary (GB) in Cu revealed an unusual non-Arrhenius behavior suggestive of a possible structural transformation Divinski et al., [Phys. Rev. B 85, 144104 (2012)]. On the other hand, atomistic computer simulations have recently discovered phase transformations in high-angle GBs in metals Frolov et al., [Nat. Commun. 4, 1899 (2013)]. In this Letter we report on atomistic simulations of Ag diffusion and segregation in two different structural phases of the Cu $\Sigma 5(310)$ GB which transform to each other with temperature. The obtained excellent agreement with the experimental data validates the hypothesis that the unusual diffusion behavior seen in the experiment was caused by a phase transformation. The simulations also predict that the low-temperature GB phase exhibits a monolayer segregation pattern while the high-temperature phase features a bilayer segregation. Together, the simulations and experiment provide the first convincing evidence for the existence of structural phase transformations in high-angle metallic GBs and demonstrate the possibility of their detection by GB diffusion measurements and atomistic simulations.

We report on structural distortions in extreme-electron density ($\sim 6\times {10}^{14}{\mathrm{cm}}^{-2}$) confined quantum wells of ${\mathrm{SrTiO}}_3$ embedded in ${\mathrm{GdTiO}}_3$. Sr-column displacements are measured using high-angle annular dark-field imaging in scanning transmission electron microscopy. Using thick ${\mathrm{SrTiO}}_3$ layers as a reference, orthorhombic-like Sr-site displacements are observed when ${\mathrm{SrTiO}}_3$ quantum wells are thinner than 4 SrO layers, in precise agreement with an experimentally observed metal-to-insulator transition. It is shown that the structural displacements are absent in thicker quantum wells, even in the immediate proximity to the orthorhombic ${\mathrm{GdTiO}}_3$. The results are discussed in the context of strong electron correlations in this system.

${\mathrm{YbRh}}_2{\mathrm{Si}}_2$ is a prototypical system for studying unconventional antiferromagnetic quantum criticality. However, ferromagnetic correlations are present which can be enhanced via isoelectronic cobalt substitution for rhodium in $\mathrm{Yb}({\mathrm{Rh}}_{1-x}{\mathrm{Co}}_x{)}_2{\mathrm{Si}}_2$. So far, the magnetic order with increasing $x$ was believed to remain antiferromagnetic. Here, we present the discovery of ferromagnetism for $x=0.27$ below $T_C=1.30\mathrm{K}$ in single crystalline samples. Unexpectedly, ordering occurs along the $c$ axis, the hard crystalline electric field direction, where the $g$ factor is an order of magnitude smaller than in the basal plane. Although the spontaneous magnetization is only $0.1{\mu }_B/\mathrm{Yb}$ it corresponds to the full expected saturation moment along $c$ taking into account partial Kondo screening.

We study the structural and magnetic orders in electron-doped ${\mathrm{BaFe}}_{2-x}{\mathrm{Ni}}_x{\mathrm{As}}_2$ by high-resolution synchrotron x-ray and neutron scatterings. Upon Ni doping $x$, the nearly simultaneous tetragonal-to-orthorhombic structural ($T_s$) and antiferromagnetic ($T_N$) phase transitions in ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ are gradually suppressed and separated, resulting in $T_s>T_N$ with increasing $x$, as was previously observed. However, the temperature separation between $T_s$ and $T_N$ decreases with increasing $x$ for $x\ge 0.065$, tending toward a quantum bicritical point near optimal superconductivity at $x\approx 0.1$. The zero-temperature transition is preempted by the formation of a secondary incommensurate magnetic phase in the region $0.088\lesssim x\lesssim 0.104$, resulting in a finite value of $T_N\approx T_c+10\mathrm{K}$ above the superconducting dome around $x\approx 0.1$. Our results imply an avoided quantum critical point, which is expected to strongly influence the properties of both the normal and superconducting states.

It has been argued that if multiple spin wave modes are competing for the same centrally located energy source, as in a nanocontact spin torque oscillator, that only one mode should survive in the steady state. Here, the experimental conditions necessary for mode coexistence are explored. Mode coexistence is facilitated by the local field asymmetries induced by the spatially inhomogeneous Oersted field, which leads to a physical separation of the modes, and is further promoted by spin wave localization at reduced applied field angles. Finally, both simulation and experiment reveal a low frequency signal consistent with the intermodulation of two coexistent modes.

We consider quantum quenches in integrable models. We argue that the behavior of local observables at late times after the quench is given by their expectation values with respect to a single representative Hamiltonian eigenstate. This can be viewed as a generalization of the eigenstate thermalization hypothesis to quantum integrable models. We present a method for constructing this representative state by means of a generalized thermodynamic Bethe ansatz (GTBA). Going further, we introduce a framework for calculating the time dependence of local observables as they evolve towards their stationary values. As an explicit example we consider quantum quenches in the transverse-field Ising chain and show that previously derived results are recovered efficiently within our framework.

Optical spectra of finite-momentum excitons in carbon nanotubes with gold nanostructures are theoretically studied. A Green function method is developed for self-consistently solving Maxwell equations including the quantum-mechanical nonlocal response of the nanotubes and the local response of the nanostructures. Excitons with finite momenta in the axis direction in the nanotubes are effectively excited by localized electric fields due to surface plasmons in the gold nanostructures and counteract the surface plasmons through depolarization fields, showing the crucial self-consistency of these effects.

The competition between two ecologically similar species that use the same resources and differ from each other only in the type of spatial motion they undergo is studied. The latter is assumed to be described either by Brownian motion or Lévy flights. Competition is taken into account by assuming that individuals reproduce in a density-dependent fashion. It is observed that no influence of the type of motion occurs when the two species are in a well-mixed unstructured state. However, as soon as the species develop spatial clustering, the one forming more concentrated clusters gets a competitive advantage and eliminates the other. A similar competitive advantage would occur between walkers of the same type but with different diffusivities if this leads also to different clustering. The coexistence of both species is also possible under certain conditions.

We investigate the ground state (GS) of a collisionless Bose-Einstein condensate (BEC) trapped in a soft one-dimensional optical lattice (OL), which is formed by two counterpropagating optical beams perturbed by the BEC density profile through the local-field effect (LFE). We show that LFE gives rise to an envelope-deformation potential, a nonlocal potential resulting from the phase deformation, and an effective self-interaction of the condensate. As a result, stable photon-atomic (polaritonic) lattice solitons, including an optical component, in the form of the deformation of the soft OL, in a combination with a localized matter-wave component, are generated in the blue-detuned setting, without any direct interaction between atoms. These self-trapped modes, which realize the system’s GS, are essentially different from the gap solitons supported by the interplay of the OL potential and collisional interactions between atoms. A transition to tightly bound modes from loosely bound ones occurs with the increase of the number of atoms in the BEC.

We demonstrate the unambiguous entangling operation of a photonic quantum-logic gate driven by an ultrabright solid-state single-photon source. Indistinguishable single photons emitted by a single semiconductor quantum dot in a micropillar optical cavity are used as target and control qubits. For a source brightness of 0.56 photons per pulse, the measured truth table has an overlap with the ideal case of $68.4\pm 0.5\%$, increasing to $73.0\pm 1.6\%$ for a source brightness of 0.17 photons per pulse. The gate is entangling: At a source brightness of 0.48, the Bell-state fidelity is above the entangling threshold of 50% and reaches $71.0\pm 3.6\%$ for a source brightness of 0.15.

We report measurements of oscillation parameters from ${\nu }_{\mu }$ and ${\overline{\nu }}_{\mu }$ disappearance using beam and atmospheric data from MINOS. The data comprise exposures of $10.71\times {10}^{20}$ protons on target in the ${\nu }_{\mu }$-dominated beam, $3.36\times {10}^{20}$ protons on target in the ${\overline{\nu }}_{\mu }$-enhanced beam, and 37.88 kton yr of atmospheric neutrinos. Assuming identical $\nu$ and $\overline{\nu }$ oscillation parameters, we measure $|\Delta m^2|=({2.41}_{-0.10}^{+0.09})\times {10}^{-3}{\mathrm{eV}}^2$ and ${sin}^2(2\theta )={0.950}_{-0.036}^{+0.035}$. Allowing independent $\nu$ and $\overline{\nu }$ oscillations, we measure antineutrino parameters of $|\Delta {\overline{m}}^2|=({2.50}_{-0.25}^{+0.23})\times {10}^{-3}{\mathrm{eV}}^2$ and ${sin}^2(2\overline{\theta })={0.97}_{-0.08}^{+0.03}$, with minimal change to the neutrino parameters.

We study the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ at a center-of-mass energy of 4.260 GeV using a $525{\mathrm{pb}}^{-1}$ data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be $(62.9\pm 1.9\pm 3.7)\mathrm{pb}$, consistent with the production of the $Y(4260)$. We observe a structure at around $3.9\mathrm{GeV}/c^2$ in the ${\pi }^{\pm }J/\psi$ mass spectrum, which we refer to as the $Z_c(3900)$. If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the ${\pi }^{\pm }J/\psi$ invariant mass spectrum, neglecting interference, results in a mass of $(3899.0\pm 3.6\pm 4.9)\mathrm{MeV}/c^2$ and a width of $(46\pm 10\pm 20)\mathrm{MeV}$. Its production ratio is measured to be $R=(\sigma \mathbf{(}{e}^{+}{e}^{-}\to {\pi }^{\pm }{Z}_c(3900{)}^{\mp }\to {\pi }^{+}{\pi }^{-}J/\psi \mathbf{)}/\sigma (e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi ))=(21.5\pm 3.3\pm 7.5)\%$. In all measurements the first errors are statistical and the second are systematic.

The cross section for $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ between 3.8 and 5.5 GeV is measured with a $967{\mathrm{fb}}^{-1}$ data sample collected by the Belle detector at or near the ${\rm Y}(nS)$ ($n=1,2,\dots ,5$) resonances. The $Y(4260)$ state is observed, and its resonance parameters are determined. In addition, an excess of ${\pi }^{+}{\pi }^{-}J/\psi$ production around 4 GeV is observed. This feature can be described by a Breit-Wigner parametrization with properties that are consistent with the $Y(4008)$ state that was previously reported by Belle. In a study of $Y(4260)\to {\pi }^{+}{\pi }^{-}J/\psi$ decays, a structure is observed in the $M({\pi }^{\pm }J/\psi )$ mass spectrum with $5.2\sigma$ significance, with mass $M=(3894.5\pm 6.6\pm 4.5)\mathrm{MeV}/c^2$ and width $\Gamma =(63\pm 24\pm 26)\mathrm{MeV}/c^2$, where the errors are statistical and systematic, respectively. This structure can be interpreted as a new charged charmoniumlike state.

Low-frequency currents induced by ultrashort laser-driven ionization can emit extremely broadband, single-cycle terahertz pulses. We present a model that predicts a strong wavelength dependence of the THz emission in good agreement with our experimental study. This reveals that the combined effects of plasma currents rising proportionally to the square of the pump wavelength and wavelength-dependent focusing conditions lead to 30 times higher THz emission at 1800 nm compared to an 800 nm wavelength. Unrivaled single-cycle electric field strengths of $4.4\mathrm{MV}/\mathrm{cm}$ are achieved with this compact table-top setup.

We investigate the coefficient of normal restitution as a function of the impact velocity, $\epsilon (v)$, for inelastic spheres. We observe oscillating behavior of $\epsilon (v)$ which is superimposed to the known decay of the coefficient of restitution as a function of impact velocity. This remarkable effect was so far unnoticed because under normal circumstances it is screened by statistical scatter. We detected its clear signature by recording large amounts of data using an automated experiment. The new effect may be understood as an interplay between translational and vibrational degrees of freedom of the colliders. Both characteristics of the oscillation, the wavelength and the amplitude, agree quantitatively with a theoretical description of the experiment.

We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence.

We present a theoretical study of an electronic quantum refrigerator based on four quantum dots arranged in a square configuration, in contact with as many thermal reservoirs. We show that the system implements the minimal mechanism for acting as a self-contained quantum refrigerator, by demonstrating heat extraction from the coldest reservoir and the cooling of the nearby quantum dot.

We have studied the magnetic field dependence of far-infrared active magnetic modes in a single ferroelectric domain ${\mathrm{BiFeO}}_3$ crystal at low temperature. The modes soften close to the critical field of 18.8 T along the [001] (pseudocubic) axis, where the cycloidal structure changes to the homogeneous canted antiferromagnetic state and a new strong mode with linear field dependence appears that persists at least up to 31 T. A microscopic model that includes two Dzyaloshinskii-Moriya interactions and easy-axis anisotropy describes closely both the zero-field spectroscopic modes as well as their splitting and evolution in a magnetic field. The good agreement of theory with experiment suggests that the proposed model provides the foundation for future technological applications of this multiferroic material.

We experimentally demonstrate all-optical interaction-free switching using the quantum Zeno effect, achieving a high contrast of $35:1$. The experimental data match a zero-parameter theoretical model for several different regimes of operation, indicating a good understanding of the switch’s characteristics. We also discuss extensions of this work that will allow for significantly improved performance, and the integration of this technology onto chip-scale devices, which can lead to ultra-low-power all-optical switching, a long-standing goal with applications to both classical and quantum information processing.