52 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
Low frequency response of a collectively pinned vortex manifold
A low frequency dynamic response of a vortex manifold in type-II
superconductor can be associated with thermally activated tunneling of large
portions of the manifold between pairs of metastable states (two-level
systems). We suggest that statistical properties of these states can be
verified by using the same approach for the analysis of thermal fluctuations
the behaviour of which is well known. We find the form of the response for the
general case of vortex manifold with non-dispersive elastic moduli and for the
case of thin superconducting film for which the compressibility modulus is
always non-local.Comment: 8 pages, no figures, ReVTeX, the final version. Text strongly
modified, all the results unchange
Characteristic length scales and formation of vortices in the Abelian Higgs model in the presence of a uniform background charge
In this brief report we consider a non-local Abelian Higgs model in the
presence of a neutralizing uniform background charge. We show that such a
system possesses vortices which key feature is a strong radial electric field.
We estimate the basic properties of such an object and characteristic length
scales in this model.Comment: Replaced with journal version. Some minor change
Hydrodynamics of liquids of arbitrarily curved flux-lines and vortex loops
We derive a hydrodynamic model for a liquid of arbitrarily curved flux-lines
and vortex loops using the mapping of the vortex liquid onto a liquid of
relativistic charged quantum bosons in 2+1 dimensions recently suggested by
Tesanovic and by Sudbo and collaborators. The loops in the flux-line system
correspond to particle-antiparticle fluctuations in the bosons. We explicitly
incorporate the externally applied magnetic field which in the boson model
corresponds to a chemical potential associated with the conserved charge
density of the bosons. We propose this model as a convenient and physically
appealing starting point for studying the properties of the vortex liquid
Creep motion in a random-field Ising model
We analyze numerically a moving interface in the random-field Ising model
which is driven by a magnetic field. Without thermal fluctuations the system
displays a depinning phase transition, i.e., the interface is pinned below a
certain critical value of the driving field. For finite temperatures the
interface moves even for driving fields below the critical value. In this
so-called creep regime the dependence of the interface velocity on the
temperature is expected to obey an Arrhenius law. We investigate the details of
this Arrhenius behavior in two and three dimensions and compare our results
with predictions obtained from renormalization group approaches.Comment: 6 pages, 11 figures, accepted for publication in Phys. Rev.
Absence of Phase Stiffness in the Quantum Rotor Phase Glass
We analyze here the consequence of local rotational-symmetry breaking in the
quantum spin (or phase) glass state of the quantum random rotor model. By
coupling the spin glass order parameter directly to a vector potential, we are
able to compute whether the system is resilient (that is, possesses a phase
stiffness) to a uniform rotation in the presence of random anisotropy. We show
explicitly that the O(2) vector spin glass has no electromagnetic response
indicative of a superconductor at mean-field and beyond, suggesting the absence
of phase stiffness. This result confirms our earlier finding (PRL, {\bf 89},
27001 (2002)) that the phase glass is metallic, due to the main contribution to
the conductivity arising from fluctuations of the superconducting order
parameter. In addition, our finding that the spin stiffness vanishes in the
quantum rotor glass is consistent with the absence of a transverse stiffness in
the Heisenberg spin glass found by Feigelman and Tsvelik (Sov. Phys. JETP, {\bf
50}, 1222 (1979).Comment: 8 pages, revised version with added references on the vanishing of
the stiffness constant in the Heisenberg spin glas
True Superconductivity in a 2D "Superconducting-Insulating" System
We present results on disordered amorphous films which are expected to
undergo a field-tuned Superconductor-Insulator Transition. Based on low-field
data and I-V characteristics, we find evidence of a low temperature
Metal-to-Superconductor transition. This transition is characterized by
hysteretic magnetoresistance and discontinuities in the I-V curves. The
metallic phase just above the transition is different from the "Fermi Metal"
before superconductivity sets in.Comment: 3 pages, 4 figure
Vortex dissipation and level dynamics for the layered superconductors with impurities
We study parametric level statistics of the discretized excitation spectra
inside a moving vortex core in layered superconductors with impurities. The
universal conductivity is evaluated numerically for the various values of
rescaled vortex velocities from the clean case to the dirty limit
case. The random matrix theoretical prediction is verified numerically in the
large regime. On the contrary in the low velocity regime, we observe
which is consistent with the theoretical
result for the super-clean case, where the energy dissipation is due to the
Landau-Zener transition which takes place at the points called ``avoided
crossing''.Comment: 10 pages, 4 figures, REVTeX3.
Superconductive proximity effect in interacting disordered conductors
We present a general theory of the superconductive proximity effect in
disordered normal--superconducting (N-S) structures, based on the recently
developed Keldysh action approach. In the case of the absence of interaction in
the normal conductor we reproduce known results for the Andreev conductance G_A
at arbitrary relation between the interface resistance R_T and the diffusive
resistance R_D. In two-dimensional N-S systems, electron-electron interaction
in the Cooper channel of normal conductor is shown to strongly affect the value
of G_A as well as its dependence on temperature, voltage and magnetic field. In
particular, an unusual maximum of G_A as a function of temperature and/or
magnetic field is predicted for some range of parameters R_D and R_T. The
Keldysh action approach makes it possible to calculate the full statistics of
charge transfer in such structures. As an application of this method, we
calculate the noise power of an N-S contact as a function of voltage,
temperature, magnetic field and frequency for arbitrary Cooper repulsion in the
normal metal and arbitrary values of the ratio R_D/R_T.Comment: RevTeX, 28 pages, 18 PostScript figures; added and updated reference
Phase diagram and upper critical field of homogenously disordered epitaxial 3-dimensional NbN films
We report the evolution of superconducting properties with disorder, in
3-dimensional homogeneously disordered epitaxial NbN thin films. The effective
disorder in NbN is controlled from moderately clean limit down to Anderson
metal-insulator transition by changing the deposition conditions. We propose a
phase diagram for NbN in temperature-disorder plane. With increasing disorder
we observe that as kFl-->1 the superconducting transition temperature (Tc) and
minimum conductivity (sigma_0) go to zero. The phase diagram shows that in
homogeneously disordered 3-D NbN films, the metal-insulator transition and the
superconductor-insulator transition occur at a single quantum critical point at
kFl~1.Comment: To appear in Journal of Superconductivity and Novel Magnetism
(ICSM2010 proceedings
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