The energy in hot electrons produced by the two plasmon decay instability, in planar targets, is measured to be the same when driven by one or two laser beams and significantly reduced with four for a constant overlapped intensity on the OMEGA EP. This is caused by multiple beams sharing the same common electron-plasma wave. A model, consistent with the experimental results, predicts that multiple laser beams can only drive a resonant common two plasmon decay electron-plasma wave in the region of wave numbers bisecting the beams. In this region, the gain is proportional to the overlapped laser beam intensity.

We investigate the formation of bound states made of two interacting atoms moving in a one dimensional (1D) quasiperiodic optical lattice. We derive the quantum phase diagram for Anderson localization of both attractively and repulsively bound pairs. We calculate the pair binding energy and show analytically that its behavior as a function of the interaction strength depends crucially on the nature—extended, multifractal, localized—of the single-particle atomic states. Experimental implications of our results are discussed.

The hysteresis or internal friction in the deformation of crystalline solids stressed cyclically is studied from the viewpoint of collective dislocation dynamics. Stress-controlled simulations of a dislocation dynamics model at various loading frequencies and amplitudes are performed to study the stress–strain rate hysteresis. The hysteresis loop areas exhibit a maximum at a characteristic frequency and a power law frequency dependence in the low frequency limit, with the power law exponent exhibiting two regimes, corresponding to the jammed and the yielding or moving phases of the system, respectively. The first of these phases of the system exhibits nontrivial critical-like viscoelastic dynamics, crossing over to intermittent viscoplastic deformation for higher stress amplitudes.

The dynamics of tracers in disordered matrices is of interest in a number of diverse areas of physics such as the biophysics of crowding in cells and cell membranes, and the diffusion of fluids in porous media. To a good approximation the matrices can be modeled as a collection of spatially frozen particles. In this Letter, we consider the effect of polydispersity (in size) of the matrix particles on the dynamics of tracers. We study a two dimensional system of hard disks diffusing in a sea of hard disk obstacles, for different values of the polydispersity of the matrix. We find that for a given average size and area fraction, the diffusion of tracers is very sensitive to the polydispersity. We calculate the pore percolation threshold using Apollonius diagrams. The diffusion constant, $D$, follows a scaling relation $D\sim ({\varphi }_c-{\varphi }_m{)}^{\mu -\beta }$ for all values of the polydispersity, where ${\varphi }_m$ is the area fraction and ${\varphi }_c$ is the value of ${\varphi }_m$ at the percolation threshold.

Surfaces with high reactivity usually have a low area percentage, which greatly limits the efficiency of surface reactivity. In this Letter we demonstrate a generic way of increasing the percentage of the highly reactive surface by using external strain. Bulk and surface elastic properties of ${\mathrm{TiO}}_2$ are studied via density functional theory calculations. The equilibrium shape of anatase ${\mathrm{TiO}}_2$ under applied strain is discussed based on the elastic properties. We find that when 5% compressive strain is applied biaxially along [100] and [010]; directions, the area percentage of the anatase (001) surface can be increased by $\sim 5$ times in comparison with the case when no strain is applied. Since the moderate strain does not introduce extrinsic defects into the material, we propose that it is an ideal way to increase the reactivity of titanium dioxide crystallites by applying biaxial compressive external strain along the $a$ axis.

Controlled dual mode scanning tunneling microscopy (STM) experiments and first-principles simulations show that the tunneling conditions can significantly alter the positive-bias topographic contrast of geometrically corrugated titania surfaces such as rutile ${\mathrm{TiO}}_2(011)\mathrm{\text{−}}(2\times 1)$. Depending on the tip-surface distance, two different contrasts can be reversibly imaged. STM simulations which either include or neglect the tip-electronic structure, carried out at three density functional theory levels of increasing accuracy, allow assignment of both contrasts on the basis of the ${\mathrm{TiO}}_2(011)\mathrm{\text{−}}(2\times 1)$ structure proposed by Torrelles et al. [Phys. Rev. Lett. 101, 185501 (2008)]. Finally, the mechanisms of contrast formation are elucidated in terms of the subtle balance between the surface geometry and the different vacuum decay lengths of the topmost $\mathrm{Ti}(3d)$ and $\mathrm{O}(2p)$ states probed by the STM-tip apex.

We report a highly unusual angular variation of the upper critical field ($H_{c2}$) in epitaxial superlattices ${\mathrm{CeCoIn}}_5(n)/{\mathrm{YbCoIn}}_5(5)$, formed by alternating layers of $n$ and a 5 unit-cell thick heavy-fermion superconductor ${\mathrm{CeCoIn}}_5$ with a strong Pauli effect and normal metal ${\mathrm{YbCoIn}}_5$, respectively. For the $n=3$ superlattice, $H_{c2}(\theta )$ changes smoothly as a function of the field angle $\theta$. However, close to the superconducting transition temperature, $H_{c2}(\theta )$ exhibits a cusp near the parallel field ($\theta =0°$). This cusp behavior disappears for $n=4$ and 5 superlattices. This sudden disappearance suggests the relative dominance of the orbital depairing effect in the $n=3$ superlattice, which may be due to the suppression of the Pauli effect in a system with local inversion symmetry breaking. Taking into account the temperature dependence of $H_{c2}(\theta )$ as well, our results suggest that some exotic superconducting states, including a helical superconducting state, might be realized at high magnetic fields.

We analyze magnetic order in Fe chalcogenide ${\mathrm{Fe}}_{1+y}\mathrm{Te}$, the parent compound of the high-temperature superconductor ${\mathrm{Fe}}_{1+y}{\mathrm{Te}}_{1-x}{\mathrm{Se}}_x$. Experiments show that magnetic order in this material contains components with momentum $Q_1=(\pi /2,\pi /2)$ and $Q_2=(\pi /2,-\pi /2)$ in the Fe only Brillouin zone. The actual spin order depends on the interplay between these two components. Previous works assumed that the ordered state has a single $\mathrm{Q}$ (either $Q_1$ or $Q_2$). In such a state, spins form double stripes along one of the diagonals breaking the rotational $C_4$ symmetry. We show that quantum fluctuations actually select another order—a double $Q$ plaquette state with equal weight of $Q_1$ and $Q_2$ components, which preserves $C_4$ symmetry. We argue that the order in ${\mathrm{Fe}}_{1+y}\mathrm{Te}$ is determined by the competition between quantum fluctuations and magnetoelastic coupling.

We present a study of the thickness dependence of magnetism and electrical conductivity in ultrathin ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_3$ films grown on ${\mathrm{SrTiO}}_3$ (110) substrates. We found a critical thickness of 10 unit cells below which the conductivity of the films disappeared and simultaneously the Curie temperature increased, indicating a magnetic insulating phase at room temperature. These samples have a Curie temperature of about 560 K with a significant saturation magnetization of $1.2\pm 0.2{\mu }_B/\mathrm{Mn}$. The canted antiferromagnetic insulating phase in ultra thin films of $n<10$ coincides with the occurrence of a higher symmetry structural phase with a different oxygen octahedra rotation pattern. Such a strain engineered phase is an interesting candidate for an insulating tunneling barrier in room temperature spin polarized tunneling devices.

We report on magnetic field-induced oscillations of the photon echo signal from negatively charged excitons in a $\mathrm{CdTe}/(\mathrm{Cd},\mathrm{Mg})\mathrm{Te}$ semiconductor quantum well. The oscillatory signal is due to Larmor precession of the electron spin about a transverse magnetic field and depends sensitively on the polarization configuration of the exciting and refocusing pulses. The echo amplitude can be fully tuned from the maximum down to zero depending on the time delay between the two pulses and the magnetic-field strength. The results are explained in terms of the optical Bloch equations accounting for the spin level structure of electrons and trions.

Our examination of the optical properties of small gold chains containing up to 24 atoms doped with a transition metal (TM) atom (Ni, Rh, Fe), using the time-dependent density functional theory, show the splitting of the collective plasmon peak. We associate the additional peak with a local plasmonic mode which corresponds to charge oscillations around the potential created by the $d$ orbitals of the impurity atoms. The effect is almost independent of the position of the TM atom in the chain, as long as it is not at the chain edge. This behavior is opposite to that of larger noble-metal-TM clusters (radius $>1\mathrm{nm}$), in which doping with TM atoms does not lead to generation of new modes, and often produces a suppression of the main plasmon peak.

The core-collapse supernova phenomenon, one of the most explosive events in the Universe, presents a challenge to theoretical astrophysics. Of the large variety of forms of matter present in core-collapse supernova, we focus on the transitional region between homogeneous (uniform) and inhomogeneous (pasta) phases. A three-dimensional, finite temperature Skyrme-Hartree-Fock $(3\mathrm{D}\mathrm{\text{−}}\mathrm{SHF})+\mathrm{BCS}$ calculation yields, for the first time fully self-consistently, the critical density and temperature of both the onset of the pasta in inhomogeneous matter, consisting of neutron-rich heavy nuclei and a free neutron and electron gas, and its dissolution to a homogeneous neutron, proton, and electron liquid. We also identify density regions for different pasta formations between the two limits. We employ four different forms of the Skyrme interaction, SkM*, SLy4, NRAPR, and SQMC700 and find subtle variations in the low density and high density transitions into and out of the pasta phase. One new stable pasta shape has been identified, in addition to the classic ones, on the grid of densities and temperatures used in this work. Our results are critically compared to recent calculations of pasta formation in the quantum molecular dynamics approach and Thomas-Fermi and coexisting phase approximations to relativistic mean-field models.

The passage of muons through matter is dominated by the Coulomb interaction with electrons and nuclei. The interaction with the electrons leads to continuous energy loss and stopping of the muons. The interaction with nuclei leads to angle “diffusion.” Two muon-imaging methods that use flux attenuation and multiple Coulomb scattering of cosmic-ray muons are being studied as tools for diagnosing the damaged cores of the Fukushima reactors. Here, we compare these two methods. We conclude that the scattering method can provide detailed information about the core. Attenuation has low contrast and little sensitivity to the core.

Friction is always present when surfaces in contact are set in motion. In this work I describe how a precise, active control of the global friction is possible by adjusting the local molecular conformation of a polyelectrolyte coating via the application of an alternating electric field. The intensity of the applied field determines the degree of interpenetration between polymer brushes in contact, regulating chain stretching while sliding, which is the process at the origin of the global friction. The dynamics of the problem is controlled by the relaxation times of the polyelectrolyte.

Electrochemical cells containing two electrodes dipped in an ionic solution are widely used as charge accumulators, either with polarizable (supercapacitor) or nonpolarizable (battery) electrodes. Recent applications include desalination (“capacitive deionization”) and energy extraction from salinity differences (“capacitive mixing”). In this Letter, we analyze a general relation between the variation of the electric potential as a function of the concentration and the salt adsorption. This relation comes from the evaluation of the electrical and mechanical energy exchange along a reversible cycle, which involves salt adsorption and release by the electrodes. The obtained relation thus describes a connection between capacitive deionization and capacitive mixing. We check this relation with experimental data already reported in the literature, and moreover by some classical physical models for electrodes, including polarizable and nonpolarizable electrodes. The generality of the relation makes it very useful in the study of the properties of the electric double layer.

In a number of recent experiments with microwave high quality superconducting coplanar waveguide resonators an anomalously weak power dependence of the quality factor has been observed. We argue that this observation implies that the monochromatic radiation does not saturate the two level systems (TLS) located at the interface oxide surfaces of the resonator and suggests the importance of their interactions. We estimate the microwave loss due to interacting TLS and show that the interactions between TLS lead to a drift of their energies that result in a much slower, logarithmic dependence of their absorption on the radiation power in agreement with the data.

We propose a scheme allowing us to observe the evolution of a quantum system in the semiclassical regime along the paths generated by the propagator. The scheme relies on performing consecutive weak measurements of the position. We show how “weak trajectories” can be extracted from the pointers of a series of devices having weakly interacted with the system. The properties of these weak trajectories are investigated and illustrated in the case of a time-dependent model system.

We show that the Hamiltonian of a multiband spin-orbit coupled semiconductor nanowire with Zeeman splitting and $s$-wave superconductivity is approximately chiral symmetric. The chiral symmetry becomes exact when only one pair of confinement bands is occupied and the Zeeman splitting is parallel to the nanowire. In this idealized case the Hamiltonian is in the BDI symmetry class of the topological classification of band Hamiltonians, allowing an arbitrary integer number of zero-energy Majorana fermion modes at each end. In the realistic case of multiband wires (Zeeman splitting still parallel to the length) the chiral symmetry is approximate and results in multiple near-zero-energy end states with increasing Zeeman splitting. The existence of such low energy end states implies the vanishing of the minigap with increased Zeeman splitting which can only be restored by breaking the approximate chiral symmetry by a second Zeeman field.

We perform quantum tomography on one-dimensional polariton condensates, spontaneously occurring in linear disorder valleys in a CdTe planar microcavity sample. By the use of optical interferometric techniques, we determine the first-order coherence function and the amplitude and phase of the order parameter of the condensate, providing a full reconstruction of the single particle density matrix for the polariton system. The experimental data are used as input to theoretically test the consistency of the Penrose-Onsager criterion for Bose-Einstein condensation in the framework of nonequilibrium polariton condensates. The results confirm the pertinence and validity of the criterion for a nonequilibrium condensed gas.

According to the quantum Zeno effect (QZ), frequent observations of a system can dramatically slow down its dynamical evolution. We show that the QZ is a physical consequence of the statistical indistinguishability of neighboring quantum states. The time scale of the problem is expressed in terms of the Fisher information and we demonstrate that the Zeno dynamics of particle entangled states might require quite smaller measurement intervals than classically correlated states. We propose an interferometric experiment to test the prediction.