Table of contents

Graphene transport at high carrier densities using a polymer electrolyte gate Bose-Einstein condensation of bound magnon pairs Cyclic competition of four species: Mean-field theory and stochastic evolution Wafer-scale graphene/ferroelectric hybrid devices for low-voltage electronics

Work can be extracted from a single heat bath if additional information is available. For the paradigmatic case of a Brownian particle in a harmonic potential, whose position has been measured with finite precision, we determine the optimal protocol for manipulating the center and stiffness of the potential in order to maximize this work in a finite-time process. The bound on this work imposed by a generalized-second-law inequality involving information can be reached only if both position and stiffness of the potential are controlled and the process is quasistatic. Estimates on the power delivered by such an "information machine" operating cyclically follow from our analytical results.

Through a redefinition of patterns in a Hopfield-like model, we introduce and develop an approach to model discrete systems made up of many, interacting components with inner degrees of freedom. Our approach highlights the intrinsic connection between the kind of interactions among components and the emergent topology describing the system itself; also, it allows to effectively address the statistical mechanics on the resulting networks. Indeed, a wide class of analytically treatable, weighted random graphs with a tunable level of correlation can be recovered and controlled. We especially focus on the case of imitative couplings among components endowed with similar patterns (i.e. attributes), which naturally gives rise to small-world effects. We also solve the thermodynamics (at a replica symmetric level) by extending the double stochastic stability technique: free energy, self-consistency relations and fluctuation analysis for a picture of criticality are obtained. Finally, applications are considered, with particular attention to the agreement among the non-trivial features predicted by the theory and the experimental findings.

Kinetically Constrained Models (KCMs) have been widely studied in the context of glassy dynamics, focusing on the influence of dynamical constraints on the slowing-down of the dynamics of a macroscopic system. In these models, it has been shown using the thermodynamic formalism for histories, that there is a coexistence between an active and an inactive phase. This coexistence can be described by a first-order transition, and a related discontinuity in the derivative of the large-deviation function for the activity. We show that adding a driving field to a KCM model does not destroy this first-order transition for the activity. Moreover, a singularity is also found in the large-deviation function of the current at large fields. We relate for the first time this property to microscopic structures, in particular the heterogeneous, intermittent dynamics of the particles, transient shear-banding and blocking walls. We describe both the shear-thinning and the shear-thickening regimes, and find that the behaviour of the current is well reproduced by a simple model.

We propose a new scheme for observing Josephson oscillations and macroscopic quantum self-trapping in a toroidally confined Bose-Einstein condensate: a dipolar self-induced Josephson junction. Polarizing the atoms perpendicularly to the trap symmetry axis, an effective ring-shaped, double-well potential is achieved which is induced by the dipolar interaction. By numerically solving the three-dimensional time-dependent Gross-Pitaevskii equation we show that coherent tunneling phenomena such as Josephson oscillations and quantum self-trapping can take place. The dynamics in the self-induced junction can be qualitatively described by a two-mode model taking into account both s-wave and dipolar interactions.

The magnetohydrodynamics (MHD) harmonic modes as well as the underlying physics have been investigated in detail by applications of the Hilbert-Huang transform (HHT), higher-order spectrum (HOS) analysis and Fourier transform (FT), based on the novel tangential X-ray (TX) diagnostic (Li E. et al., Rev. Sci. Instrum., 81 (2010) 106102). Those signal process methods were applied to a rotating m/n=2/1 magnetic island, and it was found that its second-order harmonic m/n=4/2 appearing in FT spectrum (m, n are poloidal and toroidal mode numbers, respectively) was not an intrinsic mode, but a measure of distortion of the saturated magnetic island m/n=2/1.

Dirac's method of classical analogy is employed to include quantum degrees of freedom into a geometric framework of nonequilibrium thermodynamics. The proposed formulation of dissipative quantum mechanics builds entirely upon the geometric structures implied by commutators and canonical correlations. A lucid formulation of a nonlinear quantum master equation follows from the thermodynamic structure. The approach is applicable even at very low temperatures and complex classical environments with internal structure can be handled readily.

We generalize the usual gauge transformations connected with the 1-form gauge potential to the Becchi-Rouet-Stora-Tyutin (BRST) and anti-BRST symmetry transformations for the four (3+1)-dimensional (4D) topologically massive non-Abelian gauge theory that incorporates the famous (B ∧ F) term where there is an explicit topological coupling between 1-form and 2-form gauge fields. A novel feature of our present investigation is the observation that the (anti-)BRST symmetry transformations for the auxiliary 1-form field (K_μ) and 2-form gauge potential (B_0i) are not generated by the (anti-)BRST charges that are derived by exploiting all the relevant (anti-)BRST symmetry transformations corresponding to all the fields of the present theory. This observation is a new result because it is drastically different from the application of the BRST formalism to (non-)Abelian 1-form and Abelian 2-form as well as 3-form gauge theories.

A model based on a microscopic Brueckner-Hartree-Fock approach of hyperonic matter supplemented with additional simple phenomenological density-dependent contact terms is employed to estimate the effect of hyperonic three-body forces on the maximum mass of neutron stars. Our results show that although hyperonic three-body forces can reconcile the maximum mass of hyperonic stars with the current limit of 1.4–1.5M_⊙, they are unable to provide the repulsion needed to make the maximum mass compatible with the observation of massive neutron stars, such as the recent measurements of the unusually high masses of the millisecond pulsars PSR J1614-2230 (1.97±0.04M_⊙) and PSR J1903+0327 (1.667±0.021M_⊙).

We consider system of hyperbolic balance laws governing relativistic two-fluid flow in which entropy is produced only by disequilibrium between the temperatures of the fluids. We compare two such models: one in which thermal equilibrium is attained through a relaxation procedure, and a fully relaxed model. We describe how the relaxation procedure may be made consistent with the second law of thermodynamics. The wave velocities for both models are obtained and compared: the mixture hydrodynamical velocity of the relaxed system is always less than the hydrodynamical velocity of the relaxation system.

High-order harmonic generation (HHG) with relativistically strong laser pulses is considered from multiply charged ions in counterpropagating, linearly polarized attosecond pulse trains. The propagation of the harmonics through the medium and the scaling of HHG into the multi-kilo-electronvolt regime are investigated. We show that the phase-mismatch caused by the free electron background can be compensated by an additional phase of the emitted harmonics specific to the considered setup which depends on the delay time between the pulse trains. This renders feasible the phase-matched emission of harmonics with photon energies of several tens of kilo-electronvolt from an underdense plasma.

The steady states of two vibrated granular gases separated by an adiabatic piston are investigated. The system exhibits a non-equilibrium phase transition with a spontaneous symmetry breaking. Even if the gases at both sides of the piston have the same number of particles and are mechanically identical, their steady volumes and temperatures can be rather different. The transition can be explained by a simple kinetic theory model expressing mechanical equilibrium and the energy balance occurring in the system. The model predictions are in good agreement with molecular dynamics simulation results. The macroscopic description of the steady states is discussed, as well as some physical implications of the symmetry breaking.

Light absorption by a spatially uniform spherical nanoparticle in the vicinity of surface plasmon (polariton) resonances is studied in detail based on the exact Mie solution. It is shown that the maximal absorption is achieved for a particle from weakly dissipating materials and may have very unusual properties. A simple universal formula describing the resonant absorption lineshape as a function of the particle size and its complex dielectric permittivity is obtained. Possible comparison with experiment is discussed.

Analytical study of terahertz (THz) radiation generation due to wakefields produced by propagation of short laser pulses in magnetized, homogeneous plasma, in the mildly relativistic regime has been presented. The uniform magnetic field is applied along a direction perpendicular to the electric vector as well as the propagation direction of the laser field. A perturbative technique is used to obtain electric and magnetic wakefields generated within and behind the laser pulse. It is seen that the coupling of the slow velocities with the transverse magnetic field leads to on-axis THz radiation generation.

The size effect of materials on the phase structure has been proved by many experiments, and here for the first time, we proposed a size-temperature phase diagram of gallium (Ga). We found that liquid Ga as well as its solid-liquid phase transition (PT) is size dependent. This PT phenomenon was successfully explained in terms of nucleation theory. The size-temperature phase diagram offered a universal phenomenological explanation for the size-related phase selection of Ga. This finding would enrich the general knowledge about the new phenomena induced by the finite-size effect.

We discuss the drainage of a wetting film deposited on a vertical solid covered with a regular array of microposts. It is shown that the classical Jeffreys' law, observed on flat solid, is deeply modified by the texture: 1) the film thickness does not follow anymore a scaling law, as a function of time; 2) below a critical thickness on the order of the pillar height, the film thickness drastically decreases; 3) at long time, a residual film remains trapped in the network of posts. All these facts are interpreted by considering the interaction between the "free film" flowing above the posts, and the "trapped film" inside the roughness. Beside a general description of the drainage of film on rough surfaces, our study shows that textures can be used to influence, or even block, the flow of liquid films on inclines.

Ultra-thin silicon nitride films grown by exposure of Si(111) substrates to a flux of atomic nitrogen at temperatures between 700 ^°C and 1050 ^°C have been investigated by means of X-ray spectromicroscopy, atomic force microscopy, X-ray reflectivity, and X-ray photoemission spectroscopy. The films show a Si₃N₄ stoichiometry. For reactive nitride growth at temperatures below 800 ^°C, a smooth surface and interface morphology is found. Higher temperatures lead to the formation of rough films with holes and grooves of increasing size, approaching a lateral size of several hundred nanometers for growth temperatures above 900 ^°C. Nonetheless, X-ray spectromicroscopy shows that the bottom of the holes consists of Si₃N₄.

Using magnetic, thermal and neutron measurements we show that Rb₄Mn(MoO₄)₃ is a quasi-2D triangular Heisenberg antiferromagnet with easy-axis anisotropy and successive transitions bracketing an intermediate collinear phase. An accurate quantitative account of the phase diagram is achieved through Monte Carlo simulation of a spin Hamiltonian with easy-axis anisotropy D=0.22J.

Transport measurements along the least conducting direction of the organic superconductors (TMTSF)₂PF₆ and (TMTSF)₂ClO₄ reveal a pronounced sublinear temperature dependence visible up to about four times the superconducting T_c either when pressure is close to the critical pressure for superconductivity in (TMTSF)₂PF₆ or under ambient pressure in (TMTSF)₂ClO₄ and ClO₄-ReO₄ solid solutions. Given the linear temperature dependence of the single-particle scattering in the metallic state derived from a previous investigation, the excess conduction insensitive to magnetic field but suppressed by lattice defects in the solid solution has been ascribed to sliding of fluctuating spin density waves in the vicinity of the antiferromagnetic order. This is the first observation of fluctuating spin density waves contributing to conduction.

We study the partial swapping of the Fano resonance in a correlated double-quantum-dot (DQD) system connected to normal leads by employing the Keldysh non-equilibrium Green function technique in a Coulomb blockade regime. Two types of asymmetries have been considered which occurs when the DQD system undergoes transition from symmetric parallel to i) series and ii) T-shape geometries. It is found that both types of asymmetries exhibit swapping on varying the interdot Coulomb interaction (U₁₂), however, mostly in the first one or first two pairs (out of four pairs) of Fano and Breit-Wigner peaks. Further, for particular values of U₁₂ and dot-lead couplings, one, two or three Fano peaks collapse forming bound states in the continuum (BIC). This partial (non-magnetic) swapping and the formation of BIC is found to result from an interplay of correlation effects and asymmetries in dot-lead couplings.

We present a robust scheme to derive effective models non-perturbatively for quantum lattice models when at least one degree of freedom is gapped. A combination of graph theory and the method of continuous unitary transformations (gCUTs) is shown to efficiently capture all zero-temperature fluctuations in a controlled spatial range. The gCUT can be used either for effective quasi-particle descriptions or for effective low-energy descriptions in case of infinitely degenerate subspaces. We illustrate the method for 1d and 2d lattice models yielding convincing results in the thermodynamic limit. We find that the recently discovered spin liquid in the Hubbard model on the honeycomb lattice lies outside the perturbative strong-coupling regime. Various extensions and perspectives of the gCUT are discussed.

Most laser-induced femtosecond magnetism investigations are done in magnetic thin films. Nanostructured magnetic dots, with their reduced dimensionality, present new opportunities for spin manipulation. Here we predict that if a magnetic dot has a dipole-forbidden transition between the lowest occupied molecular orbital (LUMO) and the highest unoccupied molecular orbital (HOMO), but a dipole-allowed transition between LUMO+1 and HOMO, electromagnetically induced transparency can be used to prevent ultrafast laser-induced spin momentum reduction, or spin protection. This is realized through a strong dump pulse to funnel the population into LUMO+1. If the time delay between the pump and dump pulses is longer than 60 fs, a population inversion starts and spin switching is achieved. These predictions are detectable experimentally.

Excitons in quantum wells, generated by a laser pulse, typically diffuse only a few micrometers from the spot where they are created. Solving the Gross-Pitaevskii equation we describe a free superflow of a two-dimensional slowly decaying Bose liquid. In contrast to previous theoretical models describing the luminescence ring formation in quantum wells via the conventional diffusion of electrons and holes, we explain this phenomenon as a sequence of superfluidity of excitons in a dark state. We propose a few key experiments which can further verify the exciton superfluid.

We consider a simple model for examining the effects of quenched disorder on drag consisting of particles interacting via a Yukawa potential that are placed in two coupled one-dimensional channels. The particles in one channel are driven and experience a drag from the undriven particles in the second channel. In the absence of pinning, for a finite driving force there is no pinned phase; instead, there are two dynamical regimes of completely coupled or locked flow and partially coupled flow. When pinning is added to one or both channels, we find that a remarkably rich variety of dynamical phases and drag effects arise that can be clearly identified by features in the velocity force curves. The presence of quenched disorder in only the undriven channel can induce a pinned phase in both channels. Above the depinning transition, the drag on the driven particles decreases with increasing pinning strength, and for high enough pinning strength, the particles in the undriven channel reach a reentrant pinned phase which produces a complete decoupling of the channels. We map out the dynamic phase diagrams as a function of pinning strength and the density of pinning in each channel. Our results may be relevant for understanding drag coupling in 1D Wigner crystal phases, and the effects we observe could also be explored using colloids in coupled channels produced with optical arrays, vortices in nanostructured superconductors, or other layered systems where drag effects arise.

Using particle-based simulations, we show that anomalous diffusion in two-dimensional (2D) environments induces a strongly fractal reaction kinetics, i.e. time-dependent rate coefficients. While non-classical kinetics is anticipated already for normal diffusion due to the compactness of Brownian motion in 2D, the effect is even more pronounced when particles move via subdiffusion. As a consequence, strong reactant segregation is observed. Based on these findings, we argue that the experimentally observed subdiffusion of proteins on biomembranes may serve as a means to foster biochemical reactions in well-defined "hot spots" without the need for diffusion barriers.

We derive an analytic expression for the bending elastic energy of short DNA molecules, valid in the entire range from low to high energies. The elastic energy depends on three parameters: the length of the molecule (2L), the bending modulus B, and a critical torque τ_c at which the molecule develops a kink. In the kinked state, the elastic energy is linear in the kink angle, i.e. the torque at the kink is constant (=τ_c). τ_c depends (weakly) on the sequence around the nick, but is about 27 pN×nm. We measure it for a specific sequence, through experiments where the elastic energy of constrained DNA molecules is directly measured.

Incorporating dynamic contact networks and delayed awareness into a contagion model with memory, we study the spreading patterns of infectious diseases in connected populations. It is found that the spread of an infectious disease is not only related to the past exposures of an individual to the infected but also the time scales of risk perception reflected in the social-network adaptation. The epidemic threshold p_c is found to decrease with the rise of the time scale parameter s and the memory length T, which satisfies the equation . Both the lifetime of the epidemic and the topological property of the evolved network are considered. The standard deviation σ_d of the degree distribution increases with the rise of the absorbing time t_c, a power-law relation σ_d=mt_c^γ is found.

In this paper, we study two large data sets containing the information of two different human behaviors: blog-posting and wiki-revising. In both cases, the interevent time distributions decay as power laws at both individual and population level. Unlike previous studies, we put emphasis on time scales and obtain heterogeneous decay exponents in the intra- and inter-day range for the same dataset. Moreover, we observe opposite trend of exponents in relation to individual Activity. Further investigations show that the presence of intra-day activities mask the correlation between consecutive inter-day activities and lead to an underestimate of Memory, which explain the contradicting results in recent empirical studies. Removal of data in intra-day range reveals the high values of Memory and lead us to convergent results between wiki-revising and blog-posting.

In this letter, we introduce an aspiration-induced reconnection mechanism into the spatial public-goods game. A player will reconnect to a randomly chosen player if its payoff acquired from the group centered on the neighbor does not exceed the aspiration level. We find that an intermediate aspiration level can promote cooperation best. This optimal phenomenon can be explained by a negative feedback effect, namely, intermediate aspiration level is able to result in a weak peak of reconnection, which will effectively change the downfall of cooperators and facilitate the fast spreading of cooperation. While insufficient reconnection and excessive reconnection induced by low and high aspiration levels are not conductive to such an effect. Moreover, we find that the intermediate aspiration level can lead to the heterogeneous distribution of degree, which will be beneficial to the evolution of cooperation.

Noisy signals in many real-world systems display long-range autocorrelations and long-range cross-correlations. Due to periodic trends, these correlations are difficult to quantify. We demonstrate that one can accurately quantify power-law cross-correlations between different simultaneously recorded time series in the presence of highly non-stationary sinusoidal and polynomial overlying trends by using the new technique of detrended cross-correlation analysis with varying order ℓ of the polynomial. To demonstrate the utility of this new method —which we call DCCA-ℓ(n), where n denotes the scale— we apply it to meteorological data.