229 research outputs found
Microwave response of an NS ring coupled to a superconducting resonator
A long phase coherent normal (N) wire between superconductors (S) is
characterized by a dense phase dependent Andreev spectrum . We probe this
spectrum in a high frequency phase biased configuration, by coupling an NS ring
to a multimode superconducting resonator. We detect a dc flux and frequency
dependent response whose dissipative and non dissipative components are related
by a simple Debye relaxation law with a characteristic time of the order of the
diffusion time through the N part of the ring. The flux dependence exhibits
periodic oscillations with a large harmonics content at temperatures
where the Josephson current is purely sinusoidal. This is explained considering
that the populations of the Andreev levels are frozen on the time-scale of the
experiments.Comment: 5 pages,4 figure
Intermittency of Height Fluctuations and Velocity Increment of The Kardar-Parisi-Zhang and Burgers Equations with infinitesimal surface tension and Viscosity in 1+1 Dimensions
The Kardar-Parisi-Zhang (KPZ) equation with infinitesimal surface tension,
dynamically develops sharply connected valley structures within which the
height derivative is not continuous. We discuss the intermittency issue in the
problem of stationary state forced KPZ equation in 1+1--dimensions. It is
proved that the moments of height increments behave as with for length scales . The length scale is the characteristic length of the
forcing term. We have checked the analytical results by direct numerical
simulation.Comment: 13 pages, 9 figure
Random walk in a two-dimensional self-affine random potential : properties of the anomalous diffusion phase at small external force
We consider the random walk of a particle in a two-dimensional self-affine
random potential of Hurst exponent in the presence of an external force
. We present numerical results on the statistics of first-passage times that
satisfy closed backward master equations. We find that there exists a
zero-velocity phase in a finite region of the external force , where
the dynamics follows the anomalous diffusion law $ x(t) \sim \xi(F) \
t^{\mu(F)} 0<\mu(F)<1\xi(F)FF \to 0\mu(F) \propto F^aa \simeq 0.6a=1d=1\xi(F) \propto F^{-\nu}\nu
\simeq 1.29\nu=2d=1\xi(F)1/\mu(F)d=1$,
means that the particle uses the transverse direction to find lower barriers.Comment: 10 pages, 8 figures, v2=final versio
Possible Glassiness in a Periodic Long-Range Josephson Array
We present an analytic study of a periodic Josephson array with long-range
interactions in a transverse magnetic field. We find that this system exhibits
a first-order transition into a phase characterized by an extensive number of
states separated by barriers that scale with the system size; the associated
discontinuity is small in the limit of weak applied field, thus permitting an
explicit analysis in this regime.Comment: 4 pages, 2 Postscript figures in a separate file
On the Mott glass in the one-dimensional half-filled charge density waves
We study the effect of impurity pinning on a one-dimensional half-filled
electron system, which is expressed in terms of a phase Hamiltonian with the
charge degree of freedom. Within the classical treatment, the pinned state is
examined numerically. The Mott glass, which has been pointed out by Orignac et
al. [Phys. Rev. Lett 83 (1999) 2378], appears in the intermediate region where
the impurity potential competes with the commensurate potential. Such a state
is verified by calculating the soliton formation energy, the local restoring
force around the pinned state and the optical conductivity.Comment: 13 pages, 5 figures, to be published in J. Phys. Soc. Jpn. 72 No.11
(2003
Universal temperature dependence of the conductivity of a strongly disordered granular metal
A disordered array of metal grains with large and random intergrain
conductances is studied within the one-loop accuracy renormalization group
approach. While at low level of disorder the dependence of conductivity on log
T is nonuniversal (it depends on details of the array's geometry), for strong
disorder this dependence is described by a universal nonlinear function, which
depends only on the array's dimensionality. In two dimensions this function is
found numerically. The dimensional crossover in granular films is discussed.Comment: 6 pages, 6 figures, submitted to JETP Letter
Creep via dynamical functional renormalization group
We study a D-dimensional interface driven in a disordered medium. We derive
finite temperature and velocity functional renormalization group (FRG)
equations, valid in a 4-D expansion. These equations allow in principle for a
complete study of the the velocity versus applied force characteristics. We
focus here on the creep regime at finite temperature and small velocity. We
show how our FRG approach gives the form of the v-f characteristics in this
regime, and in particular the creep exponent, obtained previously only through
phenomenological scaling arguments.Comment: 4 pages, 3 figures, RevTe
Monte-Carlo calculation of longitudinal and transverse resistivities in a model Type-II superconductor
We study the effect of a transport current on the vortex-line lattice in
isotropic type-II superconductors in the presence of strong thermal
fluctuations by means of 'driven-diffusion' Monte Carlo simulations of a
discretized London theory with finite magnetic penetration depth. We calculate
the current-voltage (I-V) characteristics for various temperatures, for
transverse as well as longitudinal currents I. From these characteristics, we
estimate the linear resistivities R_xx=R_yy and R_zz and compare these with
equilibrium results for the vortex-lattice structure factor and the helicity
moduli. From this comparison a consistent picture arises, in which the melting
of the flux-line lattice occurs in two stages for the system size considered.
In the first stage of the melting, at a temperature T_m, the structure factor
drops to zero and R_xx becomes finite. For a higher temperature T_z, the second
stage takes place, in which the longitudinal superconducting coherence is lost,
and R_zz becomes finite as well. We compare our results with related recent
numerical work and experiments on cuprate superconductors.Comment: 4 pages, with eps figure
Structure of Flux Line Lattices with Weak Disorder at Large Length Scales
Dislocation-free decoration images containing up to 80,000 vortices have been
obtained on high quality BiSrCaCuO superconducting
single crystals. The observed flux line lattices are in the random manifold
regime with a roughening exponent of 0.44 for length scales up to 80-100
lattice constants. At larger length scales, the data exhibit nonequilibrium
features that persist for different cooling rates and field histories.Comment: 4 pages, 3 gif images, to appear in PRB rapid communicatio
Fractional power-law susceptibility and specific heat in low temperature insulating state of o-TaS_{3}
Measurements of the magnetic susceptibility and its anisotropy in the
quasi-one-dimensional system o-TaS_{3} in its low-T charge density wave (CDW)
ground state are reported. Both sets of data reveal below 40 K an extra
paramagnetic contribution obeying a power-law temperature dependence
\chi(T)=AT^{-0.7}. The fact that the extra term measured previously in specific
heat in zero field, ascribed to low-energy CDW excitations, also follows a
power law C_{LEE}(0,T)=CT^{0.3}, strongly revives the case of random exchange
spin chains. Introduced impurities (0.5% Nb) only increase the amplitude C, but
do not change essentially the exponent. Within the two-level system (TLS)
model, we estimate from the amplitudes A and C that there is one TLS with a
spin s=1/2 localized on the chain at the lattice site per cca 900 Ta atoms. We
discuss the possibility that it is the charge frozen within a soliton-network
below the glass transition T_{g}~40 K determined recently in this system.Comment: 7 pages, 3 figures, submitted to Europhysics Letter
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