Table of contents

We study the out-of-equilibrium steady-state properties of the Bose-Fermi-Kondo model, describing a local magnetic moment coupled to two ferromagnetic leads that support bosonic (magnons) and fermionic (Stoner continuum electrons) low-energy excitations. This model describes the destruction of the Kondo effect as the coupling to the bosons is increased. Its phase diagram comprises three non-trivial fixed points. Using a dynamical large-N approach on the Keldysh contour, we study two different non-equilibrium setups: a) a finite bias voltage and b) a finite temperature gradient, imposed across the leads. The scaling behavior of the charge and energy currents is identified and characterized for all fixed points. We report the existence of a fixed-point–dependent effective temperature, defined though the fluctuation-dissipation relations of the local spin-susceptibility in the scaling regime, which permits to recover the equilibrium behavior of both dynamical and static spin-susceptibilities.

Being able to control the neuronal spiking activity in specific brain regions is central to a treatment scheme in several brain disorders such as epileptic seizures, mental depression, and Parkinson's diseases. Here, we present an approach for controlling self-sustained oscillations by adding or removing one directed network link in coupled neuronal oscillators, in contrast to previous approaches of adding stimuli or noise. We find that such networks can exhibit a variety of activity patterns such as on-off switch, sustained spikes, and short-term spikes. We derive the condition for a specific link to be the controller of the on-off effect. A qualitative analysis is provided to facilitate the understanding of the mechanism for spiking activity by adding one link. Our findings represent the first report on generating spike activity with the addition of only one directed link to a network and provide a deeper understanding of the microscopic roots of self-sustained spiking.

A fundamental task in quantum information science is to transfer an unknown state from particle A to particle B (often in remote space locations) by using a bipartite quantum operation $\mathcal{E}^{\textit{AB}}$. We suggest the power of $\mathcal{E}^{\textit{AB}}$ for quantum state transfer (QST) to be the maximal average probability of QST over the initial states of particle B and the identifications of the state vectors between A and B. We find the QST power of a bipartite quantum operations satisfies four desired properties between two d-dimensional Hilbert spaces. When A and B are qubits, the analytical expressions of the QST power is given. The numerical result on a QST scheme via a quantum wire shows the necessity to optimize the average fidelity. In particular, we obtain the exact results of the QST power for a general two-qubit unitary transformation, and we find a necessary and sufficient condition for the two-qubit unitary gates with perfect QST.

The influence of dissipation on the fluctuation statistics of the total energy is investigated through both a phenomenological and a stochastic model for dissipative energy transfer through a cascade of states. In equilibrium the states obey equipartition and the total energy obeys the central limit theorem, giving Gaussian fluctuation. In the presence of dissipation the fluctuations can be driven non-Gaussian if there is macroscopic energy transfer from large to small scales. We are thus able to equate the non-Gaussian order parameter fluctuations in model equilibrium systems at criticality with energy fluctuations in these dissipative systems. Energy fluctuations in the phenomenological model map directly onto the $1/f^{\alpha}$-noise problem and numerical simulations of the stochastic model yield results in qualitative agreement with these predictions.

We derive a new fluctuation-dissipation relation for non-equilibrium systems with long-term memory. We show how this relation allows one to access new experimental information regarding active forces in living cells that cannot otherwise be accessed. For a silica bead attached to the wall of a living cell, we identify a crossover time between thermally controlled fluctuations and those produced by the active forces. We show that the probe position is eventually slaved to the underlying random drive produced by the so-called active forces.

Inspired by the fact that opportunities in reality are heterogeneous for individuals due to social selection, we propose an evolutionary public goods game model considering the social selection of game organizers occurring on a square lattice. We introduce a simple rule that, depending on the value of a single parameter μ, influences the selection of players that are considered as potential game organizers. For positive μ players with a high payoff will be considered more likely. Setting μ equal to zero returns the random selection of game organizers. We find that increasing the probability of selecting the wealthier individuals as game organizers can effectively promote cooperation. We show that the promotion of cooperation attributes to the dominance of the clusters of cooperative organizers in the population by investigating the evolution of spatial patterns.

We experimentally study the dynamics of centimetric robots and their interactions with rotary gears through inelastic collisions. Under the impacts of self-propelled robots, a gear with symmetric teeth diffuses with no preferred direction of motion. An asymmetric gear, however, rectifies random motion of nearby robots which, in return, exert a torque on the gear and drive it into unidirectional motion. Rectification efficiency increases with the degree of gear asymmetry. Our work demonstrates that asymmetric environments can be used to rectify and extract energy from random motion of macroscopic self-propelled particles.

We demonstrate that the energy or quasienergy level spacing distribution in dynamically localized chaotic eigenstates is excellently described by the Brody distribution, displaying the fractional power law level repulsion. This we show in two paradigmatic systems, namely for the fully chaotic eigenstates of the kicked rotator at K = 7, and for the chaotic eigenstates in the mixed-type billiard system (Robnik 1983), after separating the regular and chaotic eigenstates by means of the Poincaré Husimi function, at very high energies with great statistical significance (587654 eigenstates, starting at about 1000000 above the ground state). This separation confirms the Berry-Robnik picture, and is performed for the first time at such high energies.

We analyse a large class of superconducting beamsplitters for which the Bell parameter (CHSH violation) is a simple function of the spin detector efficiency. For these superconducting beamsplitters all necessary information to compute the Bell parameter can be obtained in Y-junction setups for the beamsplitter. Using the Bell parameter as an entanglement witness, we propose an experiment which allows to verify the presence of entanglement in Cooper pair splitters.

Effective field theories provide a simple framework for probing possible dark-matter (DM) models by re-parametrising full interactions into a reduced number of operators with smaller dimensionality in parameter space. In many cases these models have four particle vertices, e.g., $q \bar{q} \chi \bar{\chi}$, leading to the pair production of dark-matter particles, χ, at a hadron collider from initial state quarks, q. In this analysis we show that for many fundamental DM models with s-channel DM couplings to $q \bar{q}$ pairs, these effective vertices must also produce quark contact interactions (CI) of the form $q \bar{q} q \bar{q}$. The respective effective couplings are related by the common underlying theory which allows one to translate the upper limits from one coupling to the other. We show that at the LHC, the experimental limits on quark contact interactions give stronger translated limits on the DM coupling than the experimental searches for dark-matter pair production.

We study the kinetics of chiral transitions in quark matter using a phenomenological framework (Ginzburg-Landau model). We focus on the effect of inertial terms on the coarsening dynamics subsequent to a quench from the massless quark phase to the massive quark phase. The domain growth process shows a crossover from a fast inertial regime (with $L(t) \sim t (\ln t)^{1/2}$) to a diffusive Cahn-Allen regime (with $L(t)\sim t^{1/2}$).

Precipitation on rough walls under a channel flow of a supersaturated fluid can lead to dendrite pattern formation. A passive advection of a solute has a great influence on the dendrite morphology similar to the convection effect on the solidification dendrites emerging from an undercooled liquid. We show how the asymmetric dendrite growth depends on the solute advection and turbulent mixing. Implications of our study on the generic mineral scale formation phenomena are also discussed.

We address the dynamics of the solid/liquid interface of a solidifying material when the liquid phase is flowing with respect to the solid phase. To visualize the interface and independently control both the flow and the solidification conditions, we use a thin sample filled with a transparent melt. Whereas this set-up involves no flow by itself, we link it to a thermosiphon which provides an external flow source for the liquid phase. We then evidence a new instability of solid/liquid interfaces which emerges from the coupling between solidification and flow. It is oscillatory and generates two kinds of traveling waves on the interfaces. Both waves periodically modify the growth conditions of the solid phase yielding bands of composition in the solidified material. This instability is expected to widely occur in freezing media due to the usual natural occurrence of thermal or thermosolutal convective flows in their liquid phase.

We investigated the characteristics of the discharge generated by an atmospheric pressure plasma reactor that used two L-shaped electrodes and was driven by bipolar pulses having opposite polarity. Due to the difference in the surface charge distributions on the electrodes, the discharge behaviours vary greatly between the rising and falling stages of the voltage pulse. In all cases, the plasma formed inside the reactor plays an important role in suppressing a filamentary mode outside the reactor, and hence, homogeneous discharge in He can be achieved under an open-air configuration.

The effect of an external magnetic field on the anodic arc root movement inside a dc plasma torch has been investigated. In this letter, a virtual instrument technology was used to measure the arc voltage of the plasma torch at atmospheric pressure, and the rotating frequency of the anodic arc root was estimated by high-speed photography. The arc voltage fluctuation which represents the degree of the arc instability was reduced. And a new peak, whose frequency is consistent with the rotating frequency of the anodic arc root, was found in the Fast Fourier Transform spectra of the arc voltage signal. From the results, the helical instability generated directly by anodic arc rotation is put forward, and only the appropriate external magnetic field could inhibit and reduce the instability of the plasma torch and prolong the life of the anodic electrode. Furthermore, the measured voltage waveforms indicated that the arc root attachment mode would be controllable by an external magnetic field.

A plasma brush excited by DC voltage is developed with argon as working gas in the ambient air. The time evolution of the discharge current, the light emission, and the sustaining voltage are analyzed under different conditions. The self-pulsing phenomenon of the discharge is observed with oscillated voltage and intermittent current. The self-pulsing frequency ranges from several tens hertz to several hundred hertz depending on the output power and the gas flow rate. It increases with the increasing of the gas flow rate, while it decreases as the output power increases. The phenomenon is explained qualitatively based on a spatially resolved measurement about the discharge.

A new one-dimensional analytical model describing the diffusion of low-pressure electronegative plasma in homogeneous magnetic field is developed. The conditions are found when the electron diffusion becomes independent of ion diffusion, while the diffusion of the ion component depends on the electron diffusion. The model demonstrates the influence of various parameters such as power, magnetic field and gas pressure on the diffusion. The results predicted by the model are compared with the results of one-dimensional numerical modeling.

The shaping of Au particles induced by the curvature of the supporting single-walled carbon nanotube (SWCNT) was studied using molecular-dynamics simulations. Statistic results showed that two possible structures can be formed on the inner wall of a SWCNT even at the same conditions. One is the layered structure with each layer in the form of a curved {111} plane of a fcc crystal, and the other is the faceted structure. Although there is no energetic advantage between the two structures, the former is generated with higher probability, especially for small curvature radius of the SWCNT. Moreover, the layered structure leads to lower interface energy and high strain among Au-Au bonds, where the strain increases with the curvature of the SWCNT. This indicates that the minimum of the interface energy, not the global energy, primarily influences the structural formation. To release the strain energy stored in the Au particles, the faceted structure can form but with a low probability. A large strain in Au-Au bonds is not induced when the Au particle is on the flat graphene or outside the SWCNT wall because the confinement of SWCNT does not work efficiently.

We show that a triangular lattice consisting of dipolar molecules pointing orthogonally to the plane undergoes a first-order defect melting transition.

SrTiO₃ is commonly used as a substrate for growth of various oxide films. Different reconstructions at the SrTiO₃ surface have been claimed. A question is whether these survive subsequent depositions of thin films and influence film properties. Medium energy ion scattering (MEIS) was used to probe structure and composition of the surface layer of a TiO₂-terminated (001)SrTiO₃ single-crystal substrate and 1–4 unit cell (u.c.) thick LaMnO₃ epilayers. Aligned spectra indicate enrichment of Ti at the surface and a TiO₂ double-layer (DL) configuration. The DL arrangement survives pulsed-laser deposition of LaMnO₃ in a background of high oxygen pressure (5 × 10⁻² mbar) while it is destroyed at lower oxygen pressure (10⁻⁴ mbar). Simulations of random MEIS spectra indicate substantial interdiffusion and La doping of the substrate surface but all interfaces are nevertheless insulating.

The Rashba effect in quasi two-dimensional materials, such as noble metal surfaces and semiconductor heterostructures, has been investigated extensively, while interest in real two-dimensional systems has just emerged with the discovery of graphene. We present ab initio electronic structure, phonon, and molecular-dynamics calculations to study the structural stability and spin-orbit–induced spin splitting in the transition metal dichalcogenide monolayers MXY (M = Mo, W and X, Y = S, Se, Te). In contrast to the non-polar systems with X = Y, in the polar systems with X ≠ Y the Rashba splitting at the Γ-point for the uppermost valence band is caused by the broken mirror symmetry. An enhancement of the splitting can be achieved by increasing the spin-orbit coupling and/or the potential gradient.

The spectrum of excitations of the chiral superconducting ring with internal and external radii R_i, R_e (comparable with coherence length ξ) trapping a unit flux Φ₀ is calculated. We find within the Bogoliubov-de Gennes approach that there exists a pair of precisely zero-energy states when 2k_⊥(R_e − R_i)/π is integer (here k_⊥ is the momentum component in the disk plane while k_⊥ξ > 1). They are not protected by topology, but are stable under certain deformations of the system. We discuss the ways to tune the system so that it grows into such a "Majorana disk". This condition has a character of a resonance phenomenon.

We study linear response and nonequilibrium steady-state thermoelectric transport through a single-level quantum dot tunnel coupled to two reservoirs held at different temperatures as well as chemical potentials. A fermion occupying the dot interacts with those in the reservoirs by a short-ranged two-particle interaction. For parameters for which particles flow against a bias voltage from the hot to the cold reservoir this setup acts as an energy conversion device with which electrical energy is gained out of waste heat. We investigate how correlations affect its efficiency and output power. In linear response the changes in the thermoelectric properties can be traced back to the interaction-induced renormalization of the resonance line shape. In particular, small to intermediate repulsive interactions reduce the maximum efficiency. In nonequilibrium the situation is more complex and we identify a parameter regime in which, for a fixed lower bound of the output power, the efficiency increases.

We perform first-principles calculations of the magnetocrystalline anisotropy energy (MAE) of the L1₀-like Fe_xPt_1−x samples studied experimentally by Barmak and co-workers (see J. Appl. Phys., 98 (2005) 033904). The variation of composition and long-range chemical order in the samples was studied in terms of the coherent potential approximation. In accordance with experimental observations, we find that, in the presence of long-range chemical disorder, Fe-rich samples exhibit a larger MAE than stoichiometric FePt. By considering the site-and species-resolved contributions to the MAE, we infer that the MAE is primarily a function of the degree of completeness of the nominal Fe layers in the L1₀ FePt structure.

The effect of temperature on the magnetic phase separation and the parameters of spin-spiral (helical) waves is studied using a two-dimensional single-band t-t' Hubbard model. We obtained the dependence on the temperature of the parameters of helical magnetic phases and magnetic phase-separation (PS) regions. With an increase in temperature, the PS regions (AF + [Q,Q]), ([Q,Q] + [Q,π]) get substantially reduced but new PS [Q₁,π] + [Q₂,π], (AF + [Q,π]) arise. The results are used for the interpretation of the magnetic properties of cuprates.

The non-equilibrium Green's function technique is used to study the transport characteristics of double-barrier magnetic tunnel junctions. The exchange coupling strength of the electrodes is found to be crucial in deciding the magnetoresistance characteristics of these devices. At sufficiently large values of the magnetic coupling strength, the device is found to exhibit resonant tunnel magnetoresistance and its magnitude is found to be large. The existence of pure spin currents in these devices when there is antiferromagnetic coupling between the end electrodes is found to be the primary cause of resonant tunnel magnetoresistance. The influence of the band occupation of the electrodes and the many-body interaction present in the electrode regions on the spin current and magnetoresistance are also studied.

We have proposed an exactly solvable $\text{spin-}\frac{1}{2}$ model defined on 2D decorated lattices of two types. The ground-state phase diagram of the system includes different topological phases with gapless chiral edge states. We show that two types of chiral spin liquid with gapless edge modes are realized on lattices with different symmetry. The phase transition between the topological phase with chiral gapped (Chern number zero) and the topological phase with chiral gapless edge modes (Chern number $\pm 1$) occurs in the model on the square (symmetric) decorated lattice. On the rectangular (asymmetric) decorated lattice the topological phase is defined by a chiral gapless (gapped) edge mode in the x (y) direction and a chiral gapped (gapless) edge mode in another y (x) direction. We show that a $\text{spin-}\frac{1}{2}$ Kitaev model on a decorated asymmetric square lattice exhibits the quantum phase transition between topological phases with equal Chern numbers.

The theory of quasiparticle interference (QPI) for non-centrosymmetric (NCS) superconductors with Rashba spin-orbit coupling is developed using the T-matrix theory in Born approximation. We show that qualitatively new effects in the QPI pattern originate from the Rashba spin-orbit coupling: The resulting spin coherence factors lead to a distinct difference of charge-and spin-QPI and to an induced spin anisotropy in the latter even for isotropic magnetic impurity scattering. In particular a cross-QPI appears describing the spin oscillation pattern due to non-magnetic impurity scattering which is directly related to the Rashba vector. We apply our theory to a 2D model for the NCS heavy fermion unconventional superconductor CePt₃Si and discuss the new QPI features for a gap model with accidental node lines due to its composite singlet-triplet nature.

In a reaction-diffusion system, fluctuations in both diffusion and reaction events have important effects on the steady-state statistics of the system. Here, we argue through extensive lattice simulations, mean-field–type arguments, and the Doi-Peliti formalism that the collision duration statistics —i.e., the time two particles stay together in a lattice site—plays a leading role in determining the steady state of the system. We obtain approximate expressions for the average densities of the chemical species and for the critical diffusion coefficient required to sustain the reaction.

It is shown using dimensional analysis that the maximum current density J_QCL transported on application of a voltage V_g across a gap of size D follows the relation $J_{QCL} \sim \hbar^{3 - 2\alpha} V_g^\alpha/D^{5 - 2\alpha}$. The classical Child-Langmuir result is recovered at α = 3/2 on demanding that the scaling law be independent of ℏ. For a nanogap in the deep quantum regime, additional inputs in the form of appropriate boundary conditions and the behaviour of the exchange-correlation potential show that α = 5/14. This is verified numerically for several nanogaps. It is also argued that in this regime, the limiting mechanism is quantum reflection from a downhill potential due to a sharp change in slope seen by the electron on emerging through the barrier.

Molecular-dynamics simulations are presented for systems of densely grafted semiflexible macromolecules grafted to a planar non-adsorbing substrate, studying the case where the persistence length of the polymers is of the same order as their contour length so that the polymer brush may exhibit nematic order. We focus our attention on the case where the first bond must orient perpendicularly to the substrate (so the structure resembles a "Fakir's bed" for short chains and a "polymer bristle" for longer chains). When such layers are exposed to uniform compression, the pressure vs. distance relationship exhibits two stages: i) for very small compression the chains exhibit "buckling" yet maintain their average orientation perpendicular to the surface. In this stage the pressure rises rapidly, and the components of the last bond vectors in the plane parallel to the compressing piston remain randomly oriented. ii) For larger compression, the pressure decreases after a slight overshot, and then stays constant before the pressure starts to slowly rise again. In this stage, the bond vector components (of the bonds adjacent to the compressing piston) exhibit a symmetry breaking, XY-model–like orientational order develops, which then determines the orientation characterizing the collective bending of the whole chains. Surprisingly, the resilient response of stiff polymer brushes to pressure turns out to be much weaker than that of ordinary brushes made of totally flexible polymer chains.

I present dynamical mechanisms responsible for transition frequencies, which are hidden in the homoclinic (HC) to supercritical Andronov-Hopf (AH) bifurcation switching in the two-dimensional Hindmarsh-Rose (2DHR) oscillator. For this purpose, I derive frequency gradients with respect to the input current and timescale in the 2DHR oscillator. The frequency gradients are formulated with phase response curves (PRCs) by expanding the firing frequency with small perturbations of the input current and timescale on the one-dimensional phase space of the 2DHR oscillator. I thus find two different types of striking breaks in the frequency plot with respect to the timescale, the sigmoid functional frequency and the discontinuous frequency. I also show effects of the unique PRC change on these transition frequencies.

We study the dynamics of concentrated, long, semi-flexible, unknotted and unlinked ring polymers embedded in a gel by Monte Carlo simulation of a coarse-grained model. This involves the ansatz that the rings compactify into a duplex structure where they can be modelled as linear polymers. The classical polymer glass transition involves a rapid loss of microscopic freedom within the polymer molecule as the temperature is reduced toward T_g. Here we are interested in temperatures well above T_g where the polymers retain high microscopic mobility. We analyse the slowing of stress relaxation originating from inter-ring penetrations (threadings). For long polymers an extended network of quasi-topological penetrations forms. The longest relaxation time appears to depend exponentially on the ring polymer contour length, reminiscent of the usual exponential slowing (e.g., with temperature) in classical glasses. Finally, we discuss how this represents a universality class for glassy dynamics.

The detection of a large local form of non-Gaussianity is considered to be able to rule out all single field inflation models. This statement is based on the single field consistency condition. Despite the awareness of some implicit assumptions in the derivation of this condition and the demonstration of corresponding examples that illustrate these caveats, to date there is still no explicit and self-consistent model which can serve as a counterexample to this statement. We present such a model in this letter.

An important issue for earthquake prediction is the dependence of the earthquake magnitude from past seismicity. Recently, clustering in magnitude has been evidenced: earthquakes occur with higher probability close in time, space, and magnitude to previous events. An open question is if this magnitude correlations can be found in simple models for earthquakes. Here we show that the Olami-Feder-Christensen model generates synthetic catalogs which exhibit correlations between occurrence times and magnitudes of subsequent events similar to those observed in experimental catalogs. These correlations are observed only in the range of parameters where the magnitude distribution of synthetic catalogs agrees with the experimental one. The similarity of the functional form of magnitude correlations with experimental data and their dependence on temporal distances confirm that correlations found in real catalogs cannot be attributed to spurious effects related to magnitude incompleteness.

The complex network framework has been successfully applied to the analysis of climatological data, providing, for example, a better understanding of the mechanisms underlying reduced predictability during El Niño or La Niña years. Despite the large interest that climate networks have attracted, several issues remain to be investigated. Here we focus on the influence of the periodic solar forcing in climate networks constructed via similarities of monthly averaged Surface Air Temperature (SAT) anomalies. We shift the time series in each pair of nodes such as to superpose their seasonal cycles. In this way, when two nodes are located in different hemispheres we are able to quantify the similarity of SAT anomalies during the winters and during the summers. We find that data time-shifting does not significantly modify the network Area Weighted Connectivity (AWC), which is the fraction of the total area of the Earth to which each node is connected. This unexpected network property can be understood in terms of how data time-shifting modifies the strength of the links connecting geographical regions in different hemispheres, and how these modifications are washed out by averaging the AWC.