25 research outputs found

### Weak Charge Quantization on Superconducting Islands

We consider the Coulomb blockade on a superconductive quantum dot strongly
coupled to a lead through a tunnelling barrier and/or normal diffusive metal.
Andreev transport of the correlated pairs leads to quantum fluctuations of the
charge on the dot. These fluctuations result in exponential renormalization of
the effective charging energy. We employ two complimentary ways to approach the
problem, leading to the coinciding results: the instanton and the functional RG
treatment of the non-linear sigma model. We also derive the charging energy
renormalization in terms of arbitrary transmission matrix of the multi-channel
interface.Comment: 21 pages, 4 eps figures, RevTe

### Vortex-line liquid phases: Longitudinal superconductivity in the lattice London model

We study the vortex-line lattice and liquid phases of a clean type-II
superconductor by means of Monte Carlo simulations of the lattice London model.
Motivated by a recent controversy regarding the presence, within this model, of
a vortex-liquid regime with longitudinal superconducting coherence over long
length scales, we directly compare two different ways to calculate the
longitudinal coherence. For an isotropic superconductor, we interpret our
results in terms of a temperature regime within the liquid phase in which
longitudinal superconducting coherence extends over length scales larger than
the system thickness studied. We note that this regime disappears in the
moderately anisotropic case due to a proliferation, close to the flux-line
lattice melting temperature, of vortex loops between the layers.Comment: 8 pages, Revtex, with eps figures. To appear in Phys. Rev.

### Two-loop approximation in the Coulomb blockade problem

We study Coulomb blockade (CB) oscillations in the thermodynamics of a
metallic grain which is connected to a lead by a tunneling contact with a large
conductance $g_0$ in a wide temperature range, $E_Cg_0^4 e^{-g_0/2}<T<E_C$,
where $E_C$ is the charging energy. Using the instanton analysis and the
renormalization group we obtain the temperature dependence of the amplitude of
CB oscillations which differs from the previously obtained results. Assuming
that at $T < E_Cg_0^4 e^{-g_0/2}$ the oscillation amplitude weakly depends on
temperature we estimate the magnitude of CB oscillations in the ground state
energy as $E_Cg_0^4 e^{-g_0/2}$.Comment: 10 pages, 3 figure

### Strong 3D correlations in vortex system of Bi2212:Pb

The experimental study of magnetic flux penetration under crossed magnetic
fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO)
reveals remarkable field penetration pattern alteration (flux configuration
change) and superconducting current anisotropy enhancement by the in-plane
field. The anisotropy increases with the temperature rise up to $T_m = 54 \pm 2
K$. At $T = T_m$ an abrupt change in the flux behavior is found; the
correlation between the in-plane magnetic field and the out-of-plane magnetic
flux penetration disappears. No correlation is observed for $T > T_m$. The
transition temperature $T_m$ does not depend on the magnetic field strength.
The observed flux penetration anisotropy is considered as an evidence of a
strong 3D - correlation between pancake vortices in different CuO planes at $T
< T_m$. This enables understanding of a remarkable pinning observed in
Bi2212:Pb at low temperatures.Comment: 8 pages, 9 figure

### Flux Creep and Flux Jumping

We consider the flux jump instability of the Bean's critical state arising in
the flux creep regime in type-II superconductors. We find the flux jump field,
$B_j$, that determines the superconducting state stability criterion. We
calculate the dependence of $B_j$ on the external magnetic field ramp rate,
$\dot B_e$. We demonstrate that under the conditions typical for most of the
magnetization experiments the slope of the current-voltage curve in the flux
creep regime determines the stability of the Bean's critical state, {\it i.e.},
the value of $B_j$. We show that a flux jump can be preceded by the
magneto-thermal oscillations and find the frequency of these oscillations as a
function of $\dot B_e$.Comment: 7 pages, ReVTeX, 2 figures attached as postscript file

### Quantum superconductor-metal transition

We consider a system of superconducting grains embedded in a normal metal. At
zero temperature this system exhibits a quantum superconductor-normal metal
phase transition. This transition can take place at arbitrarily large
conductance of the normal metal.Comment: 13 pages, 1 figure include

### Superconductor-Insulator Transition in a Capacitively Coupled Dissipative Environment

We present results on disordered amorphous films which are expected to
undergo a field-tuned Superconductor-Insulator Transition.The addition of a
parallel ground plane in proximity to the film changes the character of the
transition.Although the screening effects expected from "dirty-boson" theories
are not evident,there is evidence that the ground plane couples a certain type
of dissipation into the system,causing a dissipation-induced phase
transition.The dissipation due to the phase transition couples similarly into
quantum phase transition systems such as superconductor-insulator transitions
and Josephson junction arrays.Comment: 4 pages, 4 figure

### Non-linear Response of the trap model in the aging regime : Exact results in the strong disorder limit

We study the dynamics of the one dimensional disordered trap model presenting
a broad distribution of trapping times $p(\tau) \sim 1/\tau^{1+\mu}$, when an
external force is applied from the very beginning at $t=0$, or only after a
waiting time $t_w$, in the linear as well as in the non-linear response regime.
Using a real-space renormalization procedure that becomes exact in the limit of
strong disorder $\mu \to 0$, we obtain explicit results for many observables,
such as the diffusion front, the mean position, the thermal width, the
localization parameters and the two-particle correlation function. In
particular, the scaling functions for these observables give access to the
complete interpolation between the unbiased case and the directed case.
Finally, we discuss in details the various regimes that exist for the averaged
position in terms of the two times and the external field.Comment: 27 pages, 1 eps figur

### Anomalous diffusion, Localization, Aging and Sub-aging effects in trap models at very low temperature

We study in details the dynamics of the one dimensional symmetric trap model,
via a real-space renormalization procedure which becomes exact in the limit of
zero temperature. In this limit, the diffusion front in each sample consists in
two delta peaks, which are completely out of equilibrium with each other. The
statistics of the positions and weights of these delta peaks over the samples
allows to obtain explicit results for all observables in the limit $T \to 0$.
We first compute disorder averages of one-time observables, such as the
diffusion front, the thermal width, the localization parameters, the
two-particle correlation function, and the generating function of thermal
cumulants of the position. We then study aging and sub-aging effects : our
approach reproduces very simply the two different aging exponents and yields
explicit forms for scaling functions of the various two-time correlations. We
also extend the RSRG method to include systematic corrections to the previous
zero temperature procedure via a series expansion in $T$. We then consider the
generalized trap model with parameter $\alpha \in [0,1]$ and obtain that the
large scale effective model at low temperature does not depend on $\alpha$ in
any dimension, so that the only observables sensitive to $\alpha$ are those
that measure the `local persistence', such as the probability to remain exactly
in the same trap during a time interval. Finally, we extend our approach at a
scaling level for the trap model in $d=2$ and obtain the two relevant time
scales for aging properties.Comment: 33 pages, 3 eps figure

### Big, Fast Vortices in the d-RVB theory of High Temperature Superconductivity

The effect of proximity to a Mott insulating phase on the superflow
properties of a d-wave superconductor is studied using the slave boson-U(1)
gauge theory model. The model has two limits corresponding to superconductivity
emerging either out of a 'renormalized fermi liquid' or out of a
non-fermi-liquid regime. Three crucial physical parameters are identified: the
size of the vortex \textit{as determined from the supercurrent it induces;} the
coupling of the superflow to the quasiparticles and the 'nondissipative time
derivative' term. As the Mott phase is approached, the core size as defined
from the supercurrent diverges, the coupling between superflow and
quasiparticles vanishes, and the magnitude of the nondissipative time
derivative dramatically increases. The dissipation due to a moving vortex is
found to vary as the third power of the doping. The upper critical field and
the size of the critical regime in which paraconductivity may be observed are
estimated, and found to be controlled by the supercurrent length scale