Interference induced metallic-like behavior of a two-dimensional hole gas in asymmetric GaAs/Inx_{x}Ga1−x_{1-x}As/GaAs quantum well

The temperature and magnetic field dependences of the conductivity of the heterostructures with asymmetric In$_x$Ga$_{1-x}$As quantum well are studied. It is shown that the metallic-like temperature dependence of the conductivity observed in the structures investigated is quantitatively understandable within the whole temperature range, $T=0.4-20$ K. It is caused by the interference quantum correction at fast spin relaxation for 0.4 K$< T < 1.5$ K. At higher temperatures, 1.5 K$<T<4$ K, it is due to the interaction quantum correction. Finally, at $T>4-6$ K, the metallic-like behavior is determined by the phonon scattering.Comment: 4 pages, 4 figure

On electromagnetic interactions for massive mixed symmetry field

In this paper we investigate electromagnetic interactions for simplest massive mixed symmetry field. Using frame-like gauge invariant formulation we extend Fradkin-Vasiliev procedure, initially proposed for investigation of gravitational interactions for massless particles in AdS space, to the case of electromagnetic interactions for massive particles leaving in (A)dS space with arbitrary value of cosmological constant including flat Minkowski space. At first, as an illustration of general procedure, we re-derive our previous results on massive spin 2 electromagnetic interactions and then we apply this procedure to massive mixed symmetry field. These two cases are just the simplest representatives of two general class of fields, namely completely symmetric and mixed symmetry ones, and it is clear that the results obtained admit straightforward generalization to higher spins as well.Comment: 17 pages. Some clarifications added. Version to appear in JHE

Level statistics inside the core of a superconductive vortex

Microscopic theory of the type of Efetov's supermatrix sigma-model is constructed for the low-lying electron states in a mixed superconductive-normal system with disorder. The developed technique is used for the study of the localized states in the core of a vortex in a moderately clean superconductor (1/\Delta << \tau << 1/\omega_0 = E_F/\Delta^2). At sufficiently low energies E << \omega_{Th}, the energy level statistics is described by the "zero-dimensional" limit of this supermatrix theory, with the effective "Thouless energy" \omega_{Th} \sim (\omega_0/\tau)^{1/2}. Within this energy range the result for the density of states is equivalent to that obtained within Altland-Zirnbauer random matrix model of class C. Nonzero modes of the sigma-model increase the mean interlevel distance \omega_0 by the relative amount of the order of [2\ln(1/\omega_0\tau)]^{-1}.Comment: 5 pages, RevTeX. One error is corrected, also two references are added. Submitted to JETP Letter

Local correlations of different eigenfunctions in a disordered wire

We calculate the correlator of the local density of states in quasi-one-dimensional disordered wires in a magnetic field, assuming that |r_1-r_2| is much smaller than the localization length. This amounts to finding the zero mode of the transfer-matrix Hamiltonian for the supersymmetric sigma-model, which is done exactly by the mapping to the three-dimensional Coulomb problem. Both the regimes of level repulsion and level attraction are obtained, depending on |r_1-r_2|. We demonstrate that the correlations of different eigenfunctions in the quasi-one-dimensional and strictly one-dimensional cases are dissimilar.Comment: 5 pages, 2 figures. v2: an error in treating the spatial dependence of correlations is correcte

Energy absorption in time-dependent unitary random matrix ensembles: dynamic vs Anderson localization

We consider energy absorption in an externally driven complex system of noninteracting fermions with the chaotic underlying dynamics described by the unitary random matrices. In the absence of quantum interference the energy absorption rate W(t) can be calculated with the help of the linear-response Kubo formula. We calculate the leading two-loop interference correction to the semiclassical absorption rate for an arbitrary time dependence of the external perturbation. Based on the results for periodic perturbations, we make a conjecture that the dynamics of the periodically-driven random matrices can be mapped onto the one-dimensional Anderson model. We predict that in the regime of strong dynamic localization W(t) ln(t)/t^2 rather than decays exponentially.Comment: 6 pages, 1 figur

On the relation between local and geometric Lagrangians for higher spins

Equations of motion for free higher-spin gauge fields of any symmetry can be formulated in terms of linearised curvatures. On the other hand, gauge invariance alone does not fix the form of the corresponding actions which, in addition, either contain higher derivatives or involve inverse powers of the d'Alembertian operator, thus introducing possible subtleties in degrees of freedom count. We suggest a path to avoid ambiguities, starting from local, unconstrained Lagrangians previously proposed, and integrating out the auxiliary fields from the functional integral, thus generating a unique non-local theory expressed in terms of curvatures.Comment: 14 pages. Contribution to the proceedings of the 1st Mediterranean Conference on Classical and Quantum Gravity, Kolymbary (Crete, Greece) September 14-18 200

Nernst effect as a probe of superconducting fluctuations in disordered thin films

In amorphous superconducting thin films of $Nb_{0.15}Si_{0.85}$ and $InO_x$, a finite Nernst coefficient can be detected in a wide range of temperature and magnetic field. Due to the negligible contribution of normal quasi-particles, superconducting fluctuations easily dominate the Nernst response in the entire range of study. In the vicinity of the critical temperature and in the zero-field limit, the magnitude of the signal is in quantitative agreement with what is theoretically expected for the Gaussian fluctuations of the superconducting order parameter. Even at higher temperatures and finite magnetic field, the Nernst coefficient is set by the size of superconducting fluctuations. The Nernst coefficient emerges as a direct probe of the ghost critical field, the normal-state mirror of the upper critical field. Moreover, upon leaving the normal state with fluctuating Cooper pairs, we show that the temperature evolution of the Nernst coefficient is different whether the system enters a vortex solid, a vortex liquid or a phase-fluctuating superconducting regime.Comment: Submitted to New. J. Phys. for a focus issue on "Superconductors with Exotic Symmetries

Thermally activated Hall creep of flux lines from a columnar defect

We analyse the thermally activated depinning of an elastic string (line tension $\epsilon$) governed by Hall dynamics from a columnar defect modelled as a cylindrical potential well of depth $V_{0}$ for the case of a small external force $F.$ An effective 1D field Hamiltonian is derived in order to describe the 2D string motion. At high temperatures the decay rate is proportional to $F^{{5}/{2}}T^{-{1}/{2}} \exp{\left [{F_{0}}/{F}-{U(F)}/{T}\right ]},$ with $F_{0}$ a constant of order of the critical force and U(F) \sim{\left ({\epsilon V_{0}})}^{{1}/{2}}{V_{0}/{F}} the activation energy. The results are applied to vortices pinned by columnar defects in superclean superconductors.Comment: 12 pages, RevTeX, 2 figures inserte