8 research outputs found
Variable-range hopping in 2D quasi-1D electronic systems
A semi-phenomenological theory of variable-range hopping (VRH) is developed
for two-dimensional (2D) quasi-one-dimensional (quasi-1D) systems such as
arrays of quantum wires in the Wigner crystal regime. The theory follows the
phenomenology of Efros, Mott and Shklovskii allied with microscopic arguments.
We first derive the Coulomb gap in the single-particle density of states,
, where is the energy of the charge excitation. We then
derive the main exponential dependence of the electron conductivity in the
linear (L), {\it i.e.} , and current
in the non-linear (NL), {\it i.e.} , response regimes ( is the
applied electric field). Due to the strong anisotropy of the system and its
peculiar dielectric properties we show that unusual, with respect to known
results, Coulomb gaps open followed by unusual VRH laws, {\it i.e.} with
respect to the disorder-dependence of and and the
values of and .Comment: (v2) Entirely re-written (some notations changed, new presentation
and new structure). Part on the Wigner crystal taken off for short. Minor
changes in results. 16 RevTex4 pages, 5 figures. (v3) Published versio
Josephson current through a precessing classical spin
International audienceA study of the dc Josephson current between two superconducting leads in the presence of a precessing classical spin is presented. The precession gives rise to a time-dependent tunnel potential which not only implies different tunneling probabilities for spin-up and spin-down quasiparticles, but introduces also a time-dependent spin-flip term. We provide an exact general analytic solution for the out-of-equilibrium steady-state permanent current between two spin-singlet superconductors as a function of the superconducting phase difference, the precession frequency and for arbitrary junction transparency. As an application we focus on the effects of the spin-flip term alone and show that the magnitude and nature of the Josephson current are indeed strongly affected by the precession of the classical spin
Bosonization approach to charge and spin dynamics of one-dimensional spin- 1 2 fermions with band curvature in a clean quantum wire
International audienc
Critical Properties of Three-Dimensional Many-Flavor QEDs
We review several variants of three-dimensional quantum electrodynamics (QED3) with Nf fermion (or boson) flavors, including fermionic (or spinorial) QED3, bosonic (or scalar) QED3, N=1 supersymmetric QED and also models of reduced QED (supersymmetric or not). We begin with an introduction to these models and their flow to a stable infra-red fixed point in the large-Nf limit. We then present detailed state-of-the-art computations of the critical exponents of these models within the dimensional regularization (and reduction) scheme(s), at the next-to-leading order in the 1/Nf expansion and in an arbitrary covariant gauge. We finally discuss dynamical (matter) mass generation and the current status of our understanding of the phase structure of these models
Critical behaviour of (2+1)-dimensional QED: 1/-corrections
International audienceWe present recently obtained results for dynamical chiral symmetry breaking studied within (2 + 1)-dimensional QED with N four-component fermions. The leading and next-to-leading orders of the 1/N expansion are computed exactly in an arbitrary non-local gauge
Statistics of charged solitons and formation of stripes
16 pages, 7 figuresThe 2-fold degeneracy of the ground state of a quasi-one-dimensional system allows it to support topological excitations such as solitons. We study the combined effects of Coulomb interactions and confinement due to interchain coupling on the statistics of such defects. We concentrate on a 2D case which may correspond to monolayers of polyacetylene or other charge density waves. The theory is developped by a mapping to the 2D Ising model with long-range 4-spin interactions. The phase diagram exhibits deconfined phases for liquids and Wigner crystals of kinks and confined ones for bikinks. Also we find aggregated phases with either infinite domain walls of kinks or finite rods of bikinks. Roughening effects due to both temperature and Coulomb repulsion are observed. Applications may concern the melting of stripes in doped correlated materials
Josephson current through a precessing spin
A study of the dc Josephson current between two superconducting leads in the presence of a precessing classical spin is presented. The precession gives rise to a time-dependent tunnel potential which not only creates different tunneling probabilities for spin-up and spin- down quasiparticles, but also introduces a time-dependent spin-flip term. In particular, we study the effects of the spin-flip term alone on the Josephson current between two spin-singlet superconductors as a function of precession frequency and junction transparency. The system displays a steady-state solution although the magnitude and nature of the current is indeed affected by the precession frequency of the classical spin