Table of contents

The instability against emission of fermionic particles by the trapping horizon of an evolving black hole is analyzed and confirmed using the Hamilton-Jacobi tunneling method. This method automatically selects one special expression for the surface gravity of a changing horizon. The results also apply to point masses embedded in an expanding universe. As a bonus of the tunneling method, we gain the insight that the surface gravity still defines a temperature parameter as long as the evolution is sufficiently slow that the black-hole pass through a sequence of quasi-equilibrium states, and that black holes should be semi-classically unstable even in a hypothetical world without bosonic fields.

The high speed of light in vacuo together with the weakness of Earth's gravity rule out any experimental detection of gravitational deflection of light on the laboratory length scale. Recent advances in coherent nonlinear optics that produce ultra-slow light in highly dispersive media with group velocities down to ∼ 10² ms⁻¹, or even less, however, open up this possibility. In this work, we present a theoretical study for a possible laboratory observation of the deflection of such an ultra slow light in the highly dispersive medium under the Earth's gravity. Our general relativistic calculation is based on the Gordon optical metric modified so as to include dispersion. The calculated linear vertical deflection turns out to be ∼0.1 mm for a horizontal traversal of 0.5 m and a group speed v_g∼10² ms⁻¹. Experimental realizability and some conceptual points involved will be briefly discussed.

We present a novel interferometer to directly implement entanglement witness measurement. This is optimal and avoids the complex task to decompose witness into local projectors. The interferometer is based on a hybrid realization of controlled-SWAP gate. We also demonstrate entanglement-witness for simple cases experimentally.

A quantum critical point is approached by applying pressure in a number of ferromagnetic and antiferromagnetic metals. The observed dependence of T_c on pressure necessarily means that the magnetic energy is coupled to the lattice. A first-order phase transition occurs if this coupling exceeds a critical value: this is inevitable if diverges as T_c approaches zero. It is argued that this is the cause of the first-order transition that is observed in many systems. Landau theory is used to obtain the phase diagram and also to predict the regions where metastable phases occur that agree well with experiments done on MnSi and other materials. The theory can be used to obtain very approximate values for the temperature and pressure at the tricritical point in terms of measured quantities. The values of the tricritical temperature for various materials obtained from Landau theory are too low but it is shown that the predicted values will rise if the effects of fluctuations are included.

The general and explicit relation between the phase time and the dwell time for quantum tunneling of a relativistically propagating particle is investigated and quantified. In analogy with previously obtained non-relativistic results, it is shown that the group delay can be described in terms of the dwell time and a self-interference delay. Lessons concerning the phenomenology of the relativistic tunneling are drawn.

The voltage-controlled Berry phases in two vertically coupled InGaAs/GaAs quantum dots are investigated theoretically. It is found that Berry phases can be changed dramatically from 0 to 2π (or 2π to 0) only by simply applying an external voltage. Under realistic conditions, as the tunneling is varied from 0.8 eV to 0.9 eV via a bias voltage, the Berry phases are altered obviously, and this can be detected in an interference experiment. The scheme is expected to be useful in constructing quantum computation based on geometric phases in an asymmetrical double quantum dot controlled by voltage.

In this paper we revisit an idea originally proposed by Mandelbrot about the possibility to observe "negative dimensions" in random multifractals. For that purpose, we define a new way to study scaling where the observation scale ℓ and the total sample length are, respectively, going to zero and to infinity. This "mixed" asymptotic regime is parametrized by an exponent χ that corresponds to Mandelbrot "supersampling exponent". In order to study the scaling exponents in the mixed regime, we use a formalism introduced in the context of the physics of disordered systems relying upon traveling wave solutions of some non-linear iteration equation. Within our approach, we show that for random multiplicative cascade models, the parameter χ can be interpreted as a negative dimension and, as anticipated by Mandelbrot, allows one to uncover the "hidden" negative part of the singularity spectrum, corresponding to "latent" singularities. We illustrate our purpose on synthetic cascade models. When applied to turbulence data, this formalism allows us to distinguish two popular phenomenological models of dissipation intermittency: We show that the mixed scaling exponents agree with a log-normal model and not with log-Poisson statistics.

In supergravity, effective superpotential relevant to dimension-five operators on proton decay processes also leads to supersymmetry-breaking terms among sfermions, dimension-four operators. These dimension-four operators induce the dimension-five operators through 1-loop diagrams dressed by gauginos. We find that, in a class of models with the anomaly mediation, the 1-loop contributions can be comparable to those at the tree level. Therefore, such operators have a great impact on the proton decay rate. Depending on a universal phase of gaugino masses and soft mass spectrum, the proton decay rate can be enhanced or suppressed.

We have investigated the role of the quantum size effects in the evaluation of the force caused by electromagnetic vacuum fluctuations between ultra-thin films, using the dielectric tensor derived from the particle in a box model. Comparison with the results obtained by adopting a continuum dielectric model shows that, for film thicknesses of 1–10 nm, the electron confinement causes changes in the force intensity with respect to the isotropic plasma model which range from 40% to few percent depending upon the film electron density and the film separation. The calculated force shows quantum size oscillations, which can be significant for film separation distances of several nanometers. The role of electron confinement in reducing the large distance Casimir force is discussed.

Using numerical simulation, injection conditions for the electron in vacuum laser acceleration are studied. The results show that different distribution of injection momentum in the longitudinal and transversal direction will drastically influence the interaction process, and there exists a gap in the frontier area qualified for acceleration. The results for different beam widths show that the gap always exists. This gap corresponds to the valley appearing in the profile of the ejection-energy/injection-angle curve (J. Phys. B, 39 (2006) 1353). Associated with the initial conditions of the interaction system, the characteristic of the ejection-energy/injection-angle curve is also analyzed.

We report an experimental investigation of the cutting of a thin brittle polymer sheet with a blunt tool. It was recently shown that the fracture path becomes oscillatory when the tool is much wider than the sheet thickness. Here we uncover two novel transitions from straight to oscillatory fracture by varying either the tilt angle of the tool or the speed of cutting, respectively. We denote these by angle and speed unzip instabilities and analyze them by quantifying both the dynamics of the crack tip and the final shapes of the fracture paths. Moreover, for the speed unzip instability, the straight crack lip obtained at low speeds exhibits out-of-plane buckling undulations (as opposed to being flat above the instability threshold) suggesting a transition from ductile to brittle fracture.

We study the generation and evolution of continuous-variable entanglement in a single-molecular-magnets (SMM) system, where the quantum coherence effect is induced by two classical electromagnetic fields (pump and control fields). Our numerical results show that the entanglement of cavity fields can be controlled efficiently by tuning the intensity and frequency detuning of control field, and the macroscopic entangled light with long entanglement time can be realized in this SMM system, over a wide range of initial states of the cavity field. This investigation can be used for achieving the macroscopic entangled light in a solid-state medium, which is much more practical than that in an atomic or molecular medium because of its flexible design.

String theoretical arguments led to the hypothesis that the ratio of viscosity to entropy of any physical system has a lower bound. Strongly coupled systems usually have a small viscosity compared to weakly coupled plasmas in which the viscosity is proportional to the mean free path. In the case of a one-component plasma the viscosity as a function of the coupling strength shows a minimum. Here we show that the ratio of viscosity to entropy of a strongly coupled one-component plasma is always above the lower bound predicted by string theory.

Low order rational numbers of the rotational transform (magnetic resonances, in short) have been considered deleterious for magnetic confinement in toroidal devices. The design and operation of stellarators has been based on the notion that either the resonances should be relegated to small volumes with high magnetic shear, or they had to be simply avoided. Low density, low collisionality discharges of the low magnetic shear TJ-II device show that these resonances can benefit electron heat confinement. Only in conditions of very low shear over an extended radial portion of the plasma, do the resonances have a detrimental effect on confinement. The experiments consist of Electron Cyclotron Heated (ECH) plasmas where a moderated Ohmic current is induced. A distinctive feature of the TJ-II Heliac is its high rotational transform.

The relation between static structure and dynamics as measured through the diffusion coefficients in viscous multicomponent metallic melts is elucidated by the example of the binary alloy Zr₆₄Ni₃₆, by a combination of neutron-scattering experiments and mode-coupling theory of the glass transition. Comparison with a hard-sphere mixture shows that the relation between the different self diffusion coefficients strongly depends on chemical short-range ordering. For the Zr-Ni example, the theory predicts both diffusivities to be practically identical. The kinetics of concentration fluctuations is dramatically slower than that of self-diffusion, but the overall interdiffusion coefficient is equally large or larger due to a purely thermodynamic prefactor. This result is a general feature for non-demixing dense melts, irrespective of chemical short-range order.

We study large-amplitude oscillations of carbon nanotubes with chiralities (m, 0) and (m, m) and predict the existence of spatially localized nonlinear modes in the form of discrete breathers. In nanotubes with the index (m, 0) we find three types of discrete breathers associate with longitudinal, radial, and torsion anharmonic vibrations, however only the twisting breathers are found to be nonradiating nonlinear modes which survive in a curved geometry described by a three-dimensional microscopic model and remain long-lived modes even in the presence of thermal fluctuations.

Microscopic defects in crystalline structure affect phonons transport and, at a macroscopic scale, heat propagation. Among them, disclinations defects change the topology by breaking the rotational symmetry in the material. Considering the Katanaev-Volovich metric for such defect description, the new phonon motion equation is derived near a disclination. Then, using the Boltzmann formalism to model phonon transport, a modified radiative transfer equation involving an effective refraction index that takes into account the disclination is introduced. The variations of the disclination index are discussed. Then, the corrections on heat flux that should be brought in such defected medium are exposed.

We present a method for the determination of the density profile of misfit dislocations in graded SiGe layers based on high-resolution X-ray diffraction and simulation of diffuse X-ray scattering from misfit dislocations. From the density profile of misfit dislocations both the profile of local plastic relaxation and the profile of the Ge content were determined; the latter compares very well with the results of depth-resolved secondary-ion mass analysis.

Self-diffusion of implanted ³¹Si in the ε-phase FeSi (cubic B20-structure) has been determined in the temperature range 660–810 ^°C using the modified radiotracer technique. With an activation enthalpy of 2.30 eV and a pre-exponential factor of 15×10⁻⁸ m² s⁻¹ the silicon diffusivity was found to be slightly slower than Ge impurity diffusion in FeSi. This difference is proposed to originate from attractive elastic interactions prevailing between the slightly oversized Ge atoms and the Si sublattice vacancies. The results confirm the argument that ⁷¹Ge radioisotopes may be used to substitute the short-lived ³¹Si radiotracers when estimating self-diffusion in silicides.

The scaling behavior of self-avoiding walks (SAWs) on the backbone of percolation clusters in two, three and four dimensions is studied by Monte Carlo simulations. We apply the pruned-enriched Rosenbluth chain growth method (PERM). Our numerical results bring about the estimates of critical exponents, governing the scaling laws of disorder averages of the end-to-end distance of SAW configurations. The effects of finite-size scaling are discussed as well.

The magnetoexcitonic optical absorption of a GaAs bulk semiconductor driven by a terahertz (THz) field is investigated numerically. The method of the solution of the initial-value problem, in combination with the perfect matched layer technique, is used to calculate the optical susceptibility, with Coulomb interaction, Landau quantization, and THz fields involved nonperturbatively. It shows that there appear replicas and sidebands of magnetoexciton of different Landau levels, which greatly enrich the magneto-optical spectrum in the presence of a driving THz field.

By first-principles calculations, we present a doping-dependent phase diagram of the LaOMAs (M=V–Cu) family. It is characterized as a antiferromagnetic semiconductor around the LaOMnAs side and as a ferromagnetic metal around LaOCoAs. Both LaOFeAs and LaONiAs, where superconductivity were discovered, are located at the borderline of magnetic phases. An extensive Fermi surface analysis suggests that the observed superconductivity is of electron type in its origin. We discuss possible pairing mechanisms in the context of competing ferromagnetic phases found in this work and the ferromagnetic spin fluctuations.

We investigate the temperature dependence of the intrinsic charge and spin transport in two-dimensional semiconductors with Rashba spin-orbit coupling. For (where α is the Rashba spin-orbit coupling parameter), the real part of the optical conductivity (σ^R(ω)) and the imaginary part of the spin Hall conductivity (σ^I_sH(ω)) decrease with temperature monotonically. Outside this frequency range, σ^R(ω) and σ^I_sH(ω) exhibit resonant behavior. At high frequencies, σ^R_sH(ω) changes sign at a characteristic temperature T₁. Our result suggests that the sign and magnitude of σ^R_sH(ω) can be tuned by changing the temperature.

We have investigated the electronic structure of graphite oxide using X-ray absorption spectroscopy at the carbon and oxygen K-edges. The unoccupied π^* and σ^* states associated with sp² hybridization in graphite, are also apparent in the graphite oxide, which indicates that it has a graphitic structure even though it experiences oxidation and annealing. Additional electronic states of the graphite oxide which are not present in its precursor, graphite, are ascribed to the functional groups such as epoxide, carboxyl, and hydroxyl groups.

It is shown that the interplay of long-range disorder and in-plane magnetic field gives rise to an out-of-plane spin polarization and a finite spin Hall conductivity of the two-dimensional electron gas in the presence of Rashba spin-orbit coupling. A key aspect is provided by the electric-field–induced in-plane spin polarization. Our results are obtained first in the clean limit where the spin-orbit splitting is much larger than the disorder broadening of the energy levels via the diagrammatic evaluation of the Kubo formula. Then the results are shown to hold in the full range of the disorder parameter αp_Fτ by means of the quasiclassical Green function technique.

We investigate the influence of impurities and vacancies in the formation of the magnetic moment in CaB₆ using full-potential ab initio band structure calculations. CaB₆ is found to be a band insulator with a band gap of about 0.2 eV. The calculated results indicate that carbon and oxygen substitutions in boron sublattice, usually expected as impurity in low-purity borons, do not play a significant role in the local moment formation. The boron vacancy in the boron sublattice, on the other hand, leads to the formation of an impurity band in the vicinity of the Fermi level, which exhibits finite exchange splitting and magnetic moment. All these results provide a remarkable representation of the experimental results. This finding of the role of vacancies in the sublattice responsible for electronic conduction is an important revelation in the understanding of ferromagnetism in the diluted electron system.

In usual superconductivity (SC), the pairs have zero total momentum irrespective of their symmetry. Staggered SC would involve, instead, pairs with a finite commensurate total momentum, but such exotic states have never been proven to be realized in nature. Here we study for the first time the influence of particle-hole asymmetry on the competition of staggered SC with Charge Density Waves (CDW) in a ferromagnetic medium. We obtain unprecedented situations in which CDW and staggered SC coexist. We also obtain cases of a SC dome near the collapse of a CDW state as well as cascades of transitions that exhibit remarkable similarities with the pressure phase diagram in UGe₂, suggesting that SC in this material may be staggered coexisting and competing with a CDW state.

We show that a new glassy phase can emerge in the presence of strong magnetic frustration and quantum fluctuations. It is a valence bond glass (VBG). We study its properties solving the Hubbard-Heisenberg model on a Bethe lattice within the large-N limit introduced by Affleck and Marston. We work out the phase diagram that contains Fermi liquid, dimer and valence bond glass phases. This new glassy phase has no electronic or spin gap (although a pseudo-gap is observed), it is characterized by long-range critical valence bond correlations and is not related to any magnetic ordering. As a consequence, it is quite different from both valence bond crystals and spin glasses.

This work presents a novel method for estimating the degree distributions of coupled chaotic oscillator networks via time series obtained from controlled measurements of networks stable dynamics. The proposed method does not require explicit analytical knowledge of the dynamic system, and can be applied to networks with various topological structures. This work focuses on networks with around 10% of possible connections between vertices, although the method generally succeeds with lesser accuracy for higher connectivity percentages. No study has evaluated the degree distribution P(k) from measured time series only. Furthermore, the proposed scheme is very robust against noise.

We present the phase diagram of a colloid-polymer mixture in which the radius a of the colloidal spheres is approximately the same as the radius R of a polymer coil (q=R/a≈1). A three-phase coexistence region is experimentally observed, previously only reported for colloid-polymer mixtures with smaller polymer chains (q≲0.6). A recently developed generalized free-volume theory (GFVT) for mixtures of hard spheres and non-adsorbing excluded-volume polymer chains gives a quantitative description of the phase diagram. Monte Carlo simulations also agree well with experiment.

Using transfer entropy, we observed the strength and direction of information flow between stock indices. We uncovered that the biggest source of information flow is America, while most receivers are in the Asia/Pacific region. According to the minimum spanning tree, the Standard and Poor's 500 Index (GSPC) is located at the focal point of the information source for world stock markets.

We have investigated the spectral density of shot noise for the system in Kondo regime irradiated with ac fields on the QD and the two terminals. In the low temperature, strong coupling, and large charging energy regime, the correlation effects influence electron transport significantly. The external ac fields split the Kondo peak to form side peaks, and the locations of the side peaks are dependent on the frequency considerably. The differential shot noise in the Kondo regime is very different from that in the non-interacting QD system. The Kondo effect and photon-assisted tunneling destroy the symmetry of shot noise. Both super-Poissonian and sub-Poissonian shot noise exist in Kondo regime. The asymmetric structure is found more evident in the derivative of shot noise for the photon-electron pumping case.

We introduce a new method for quantifying pattern-based complex short-time correlations of a time series. Our correlation measure is 1 for a perfectly correlated and 0 for a random walk time series. When we apply this method to high-frequency time series data of the German DAX future, we find clear correlations on short time scales. In order to subtract trivial autocorrelation parts from the pattern conformity, we introduce a simple model for reproducing the antipersistent regime and use alternatively level 1 quotes. When we remove the pattern conformity of this stochastic process from the original data, remaining pattern-based correlations can be observed.

Scalar perturbations can grow during a phantomic cosmological phase as the big rip is approached, in spite of the highly accelerated expansion regime, if the equation of state is such that . It is shown that such result is independent of the spatial curvature. The perturbed equations are exactly solved for any value of the curvature parameter k and of the equation of state parameter w. Growing modes are found asymptotically under the condition . Since the Hubble radius decreases in a phantom universe, such result indicates that a phantom scenario may not survive longtime due to gravitational instability.

In this letter we calculate the energy loss of a highly magnetized neutron star due to Quantum Vacuum Friction (QVF). Taking into account one-loop corrections in the effective Heisenberg-Euler Lagrangian of the light-light interaction, we derive an analytic expression for QVF allowing us to take into account a magnetic field at the surface of the star as high as 10¹¹ T. In the case of magnetars, with magnetic fields above the QED critical field, we show that the QVF is the dominating energy loss process. This has important consequences, in particular for the inferred value of the magnetic field. This also indicates the need for independent measurements of magnetic field, energy loss rate, and the braking index in order to fully characterize magnetars.