The current-voltage characteristics of two long capacitively coupled one-dimensional arrays of small Josephson junctions were measured, where the coupling capacitance was comparable with the capacitance of the junction. The current in both arrays was simultaneously measured at various applied magnetic fields with the voltage applied to only one of the arrays. The current was induced in the unbiased array beyond the threshold voltage for the Coulomb blockade of the biased array. The direction of the induced current is the same as that of the current in the other array when the applied magnetic field is small and Cooper-pair tunneling is dominant, while it changes to the opposite direction when the applied magnetic field is large and single-electron tunneling is dominant. This suggests that the current induction mechanism between arrays of small Josephson junctions is substantially different from that in arrays of small normal tunnel junctions.

We investigate the effect of edges on the intrinsic $d$-wave superconducting state in graphene doped close to the van Hove singularity. While the bulk is in a chiral $d_{x^2-y^2}+i{d}_{xy}$ state, the order parameter at any edge is enhanced and has $d_{x^2-y^2}$-symmetry, with a decay length strongly increasing with weakening superconductivity. No graphene edge is pair breaking for the $d_{x^2-y^2}$ state, and there are no localized zero-energy edge states. We find two chiral edge modes which carry a spontaneous, but not quantized, quasiparticle current related to the zero-energy momentum. Moreover, for realistic values of the Rashba spin-orbit coupling, a Majorana fermion appears at the edge when tuning a Zeeman field.

We use ${}^{75}\mathrm{As}$ nuclear magnetic resonance to investigate the local electronic properties of $\mathrm{Ba}({\mathrm{Fe}}_{1-x}{\mathrm{Ru}}_x{)}_2{\mathrm{As}}_2$ ($x=0.23$). We find two phase transitions: to antiferromagnetism at $T_N\approx 60\mathrm{K}$ and to superconductivity at $T_C\approx 15\mathrm{K}$. Below $T_N$, our data show that the system is fully magnetic, with a commensurate antiferromagnetic structure and a moment of $0.4{\mu }_B/\mathrm{Fe}$. The spin-lattice relaxation rate $1/{}^{75}T_1$ is large in the magnetic state, indicating a high density of itinerant electrons induced by Ru doping. On cooling below $T_C$, $1/{}^{75}T_1$ on the magnetic sites falls sharply, providing unambiguous evidence for the microscopic coexistence of antiferromagnetism and superconductivity.

Contrary to previous studies that classify ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ as a realization of the Heisenberg-Kitaev model with a dominant spin-orbit coupling, we show that this system represents a highly unusual case in which the electronic structure is dominated by the formation of quasimolecular orbitals (QMOs), with substantial quenching of the orbital moments. The QMOs consist of six atomic orbitals on an Ir hexagon, but each Ir atom belongs to three different QMOs. The concept of such QMOs in solids invokes very different physics compared to the models considered previously. Employing density functional theory calculations and model considerations we find that both the insulating behavior and the experimentally observed zigzag antiferromagnetism in ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ naturally follow from the QMO model.

We have found ferromagnetism in epitaxially grown superlattices of ${\mathrm{CaRuO}}_3/{\mathrm{CaMnO}}_3$ that arises in one unit cell at the interface. Scanning transmission electron microscopy and electron energy loss spectroscopy indicate that the difference in magnitude of the Mn valence states between the center of the ${\mathrm{CaMnO}}_3$ layer and the interface region is consistent with double exchange interaction among the Mn ions at the interface. Polarized neutron reflectivity and the ${\mathrm{CaMnO}}_3$ thickness dependence of the exchange bias field together indicate that the interfacial ferromagnetism is only limited to one unit cell of ${\mathrm{CaMnO}}_3$ at each interface. The interfacial moment alternates between the $1{\mu }_B/\mathrm{\text{interface}}$ Mn ion for even ${\mathrm{CaMnO}}_3$ layers and the $0.5{\mu }_B/\mathrm{\text{interface}}$ Mn ion for odd ${\mathrm{CaMnO}}_3$ layers. This modulation, combined with the exchange bias, suggests the presence of a modulating interlayer coupling between neighboring ferromagnetic interfaces via the antiferromagnetic ${\mathrm{CaMnO}}_3$ layers.

We present a compelling response of a low-dimensional strongly correlated system to an external perturbation. Using the time-dependent Lanczos method we investigate a nonequilibrium evolution of the half-filled one-dimensional extended Hubbard model, driven by a transient laser pulse. When the system is close to the phase boundary, by tuning the laser frequency and strength, a sustainable charge order enhancement is found that is absent in the Mott insulating phase. We analyze the conditions and investigate possible mechanisms of emerging charge order enhancement. Feasible experimental realizations are proposed.

We report the observation of the biexciton in semiconducting single-wall carbon nanotubes by means of nonlinear optical spectroscopy. Our measurements reveal the universal asymmetric line shape of the Fano resonance intrinsic to the biexciton transition. For nanotubes of the (9,7) chirality, we find a biexciton binding energy of 106 meV. From the calculation of the ${\chi }^{(3)}$ nonlinear response, we provide a quantitative interpretation of our measurements, leading to an estimation of the characteristic Fano factor $q$ of $7\pm 3$. This value allows us to extract the first experimental information on the biexciton stability and we obtain a biexciton annihilation rate comparable to the exciton-exciton annihilation one.

With the aid of molecular dynamics simulation, we consider why the diffusivity of liquid becomes slower as the liquid is confined to a narrower space. The diffusion coefficient of octamethylcyclotetrasiloxane liquid confined between two mica surfaces was calculated for a range of surface separations from 64 to 23 Å. The resulting separation dependence of the diffusion coefficient can be explained by considering that the molecular diffusion is an activated process. In particular, we find that the increase in the activation energy is closely correlated with the decrease of the potential energy per molecule, from which we propose a molecular-level mechanism of this confined-induced diffusion slowdown.

Nonequilibrium molecular dynamics simulations are used to show that the shear viscosity of a polymer melt can be significantly reduced when filled with small energetically neutral nanoparticles, apparently independent of the polymer’s chain length. Analogous to solvent molecules, small nanoparticles act akin to plasticizers and reduce the viscosity of a polymer melt. This effect, which persists for particles whose sizes are as large as the chain size or the entanglement mesh size, whichever is smaller, can be overcome by making the chain-nanoparticle interactions significantly attractive. Our simulations allow us to systematically organize the viscosity data of filled polymer melts, and thus provide a strong basis from which to predict the flow behavior of these commercially important class of materials.

Dynamic sorting of lipids and proteins in cellular membranes plays a critical role in establishing and maintaining distinct compositions in various organelles. Recent experiments found that the lipid sorting in a membrane tube highly depends on the pulling speed at the tip. However, the mechanism of this velocity dependence has not yet been revealed. In this Letter, we found that when a membrane is deformed rapidly, the lipid flow induced by fast membrane shape change will significantly affect the sorting results. The competition between the curvature-driven lipid sorting and the pulling-induced lipid flow leads to novel behaviors. When a membrane tube is pulled out from a liquid ordered ($L_o$) domain at a constant speed, slow pulling leads to the formation of a liquid disordered ($L_d$) tube, while fast pulling results in a $L_o$ tube. Interestingly, in a membrane tube pulled at an intermediate speed, alternate $L_d$ and $L_o$ domains appear in the tube. The sorting dynamics and the corresponding pulling force were systematically studied. The results of this study could lead to a better understanding of the dynamic sorting and traffic of lipids and proteins in living cells.

In this Letter we show that quantum nonlocality can be superactivated. That is, one can obtain violations of Bell inequalities by tensorizing a local state with itself. In the second part of this work we study how large these violations can be. In particular, we show the existence of quantum states with very low Bell violation but such that five copies of them give very large violations. In fact, this gap can be made arbitrarily large by increasing the dimension of the states.

We have measured the beam-normal single-spin asymmetry $A_n$ in the elastic scattering of 1–3 GeV transversely polarized electrons from ${}^1\mathrm{H}$ and for the first time from ${}^4\mathrm{He}$, ${}^{12}\mathrm{C}$, and ${}^{208}\mathrm{Pb}$. For ${}^1\mathrm{H}$, ${}^4\mathrm{He}$, and ${}^{12}\mathrm{C}$, the measurements are in agreement with calculations that relate $A_n$ to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the ${}^{208}\mathrm{Pb}$ result is significantly smaller than the corresponding prediction using the same formalism. These results suggest that a systematic set of new $A_n$ measurements might emerge as a new and sensitive probe of the structure of heavy nuclei.

We report the discovery of the formation of an electron Cooper pair approximately 40 eV above the double-ionization threshold in benzene, naphthalene, anthracene, and coronene after absorption of a single photon. We have measured the ratios of doubly to singly charged parent ions of the above mentioned molecules as well as pyrrole and furan by using monochromatized synchrotron radiation up to 100 eV above the corresponding thresholds. We also recorded photoelectron spectra of benzene and naphthalene at selected energies. The electron-pair formation is based on the specific structure of the molecules and does not exist for pyrrole and furan.

High resolution kinetic simulations of collisionless plasma driven by shear show the development of turbulence characterized by dynamic coherent sheetlike current density structures spanning a range of scales down to electron scales. We present evidence that these structures are sites for heating and dissipation, and that stronger current structures signify higher dissipation rates. Evidently, kinetic scale plasma, like magnetohydrodynamics, becomes intermittent due to current sheet formation, leading to the expectation that heating and dissipation in astrophysical and space plasmas may be highly nonuniform and patchy.

We measure the time oscillations of a freely evolving standing wave of phonons in a Bose-Einstein condensate. We present the technique of short Bragg pulses, which stimulates the standing wave. The subsequent oscillations are observed in situ. The frequency of the oscillations gives the dispersion relation, the amplitude gives the static structure factor, and the decay gives the dephasing time. The new technique gives orders of magnitude more sensitivity than Bragg spectroscopy, allowing for the observation of deviations from the local density approximation. Specifically, it is seen that the phonons undergo a transition from three dimensions to one dimension, when their wavelength becomes longer than the transverse radius of the condensate. The one-dimensional regime contains an inflection point in the dispersion relation, a decrease in the superfluid critical velocity, a minimum in the group velocity, and an increase in the lifetime of the standing wave oscillations.

We report on the direct observation of coherent backscattering (CBS) of ultracold atoms in a quasi-two-dimensional configuration. Launching atoms with a well-defined momentum in a laser speckle disordered potential, we follow the progressive build up of the momentum scattering pattern, consisting of a ring associated with multiple elastic scattering, and the CBS peak in the backward direction. Monitoring the depletion of the initial momentum component and the formation of the angular ring profile allows us to determine microscopic transport quantities. We also study the time evolution of the CBS peak and find it in fair agreement with predictions, at long times as well as at short times. The observation of CBS can be considered a direct signature of coherence in quantum transport of particles in disordered media. It is responsible for the so called weak localization phenomenon, which is the precursor of Anderson localization.

We report the high-resolution and broadband light-scattering spectroscopy of a single crystal of a prototypical relaxor ferroelectric, $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_3$. A self-similar broad central peak, whose intensity is expressed as $I(\omega )\propto {\omega }^{\alpha }$ has been observed, indicating the presence of a fractal in the crystal. A strong correspondence exists between the temperature dependence of the exponent $\alpha$ and that of the reported behaviors of polar nanoregions. The estimated fractal dimension ($d_f\approx 2.6$) at low temperatures clearly indicates a percolation transition of the polar nanoregions at around 240 K.

Oscillatory phenomena of compartmentalized bidisperse granular gases are studied through experiments, molecular dynamics simulations, and a flux model [Mikkelsen et al., Phys. Rev. E 70, 061307 (2004)]. The degenerate oscillatory state ($d$-OSC), which has been predicted in our previous simulations [Liu et al., Phys. Rev. E 79, 052301 (2009)], is experimentally observed and well described by the flux model. From the $d$-OSC state, the system takes a transition to a complete oscillatory state (OSC) through a homoclinic gluing bifurcation. Around the bifurcation point, noise-induced periodic irregularity is observed, and it can be perfectly reproduced by simulations and the flux model with additional random flux terms. The numerical results show a low-frequency divergence characteristic of the irregular oscillation, which is clearly caused by noise-induced hopping between OSC and $d$-OSC states.

We address the experimental estimation of Gaussian quantum discord for a two-mode squeezed thermal state, and demonstrate a measurement scheme based on a pair of homodyne detectors assisted by Bayesian analysis, which provides nearly optimal estimation for small value of discord. In addition, though homodyne detection is not optimal for Gaussian discord, the noise ratio to the ultimate quantum limit, as dictated by the quantum Cramer-Rao bound, is limited to about 10 dB.

An important task for quantum-information processing is optimal discrimination between two nonorthogonal quantum states, which until now has been realized only optically. Here, we present and compare experimental realizations of optimal quantum measurements for distinguishing between two nonorthogonal quantum states encoded in a single ${}^{14}\mathrm{N}$ nuclear spin at a nitrogen-vacancy defect in diamond. Implemented measurement schemes are the minimum-error measurement (known as Helstrom measurement), unambiguous state discrimination using a standard projective measurement, and optimal unambiguous state discrimination [known as Ivanovic-Dieks-Peres (IDP) measurement], which utilizes a three-dimensional Hilbert space. This allows us to benchmark the IDP measurement against the standard projective measurements. Measurement efficiencies are found to be above 80% for all schemes and reach a value of 90% for the IDP measurement.