732 research outputs found
Coulomb Blockade with Dispersive Interfaces
What quantity controls the Coulomb blockade oscillations if the dot--lead
conductance is essentially frequency--dependent ? We argue that it is the ac
dissipative conductance at the frequency given by the effective charging
energy. The latter may be very different from the bare charging energy due to
the interface--induced capacitance (or inductance). These observations are
supported by a number of examples, considered from the weak and strong coupling
(perturbation theory vs. instanton calculus) perspectives.Comment: 4 page
Phase slip phenomena in superconductors: from ordered to chaotic dynamics
We consider flux penetration to a 2D superconducting cylinder. We show that
in the low field limit the kinetics is deterministic. In the strong field limit
the dynamics becomes stochastic. Surprisingly the inhomogeneity in the cylinder
reduces the level of stochasticity because of the predominance of
Kelvin-Helmholtz vortices.Comment: 4 pages, 3 figures (main text) and 1 page, 1 figure (supplementary
material
Fractional-flux vortices and spin superfluidity in triplet superconductors
We discuss a novel type of fractional flux vortices along with integer flux
vortices in Kosterlitz-Thouless transitions in a triplet superconductor. We
show that under certain conditions a spin-triplet superconductor should exhibit
a novel state of {\it spin superfluidity} without superconductivity.Comment: Physical Review Lettes, in print. v2: references added, v3:
discussion of several points extended according to referee request. Latest
updates and links to related papers are available at my homepage
http://people.ccmr.cornell.edu/~egor
Chiral Correction to the Spin Fluctuation Feedback in two-dimensional p-wave Superconductors
We consider the stability of the superconducting phase for spin-triplet
p-wave pairing in a quasi-two-dimensional system. We show that in the absence
of spin-orbit coupling there is a chiral contribution to spin fluctuation
feedback which is related to spin quantum Hall effect in a chiral
superconducting phase. We show that this mechanism supports the stability of a
chiral p-wave state.Comment: 8 pages. The final version is accepted for publication in Europhys
Let
Charge relaxation resistance in the Coulomb blockade problem
We study the dissipation in a system consisting of a small metallic island
coupled to a gate electrode and to a massive reservoir via single tunneling
junction. The dissipation of energy is caused by a slowly oscillating gate
voltage. We compute it in the regimes of weak and strong Coulomb blockade. We
focus on the regime of not very low temperatures when electron coherence can be
neglected but quantum fluctuations of charge are strong due to Coulomb
interaction. The answers assume a particularly transparent form while expressed
in terms of specially chosen physical observables. We discovered that the
dissipation rate is given by a universal expression in both limiting cases.Comment: 21 pages, 12 figure
Asymptotic tunneling conductance in Luttinger liquids
Conductance through weak constrictions in Luttinger liquids is shown to
vanish with frequency as , where
is a dimensionless parameter characterizing the Luttinger liquid phase, and
and are nonuniversal constants. The first term arises from the ^^
Coulomb blockade' effect and dominates for , whereas the second
results from eliminating high-energy modes and dominates for .Comment: Latex file + one appended postcript figur
Resistance in Superconductors
In this pedagogical review, we discuss how electrical resistance can arise in
superconductors. Starting with the idea of the superconducting order parameter
as a condensate wave function, we introduce vortices as topological excitations
with quantized phase winding, and we show how phase slips occur when vortices
cross the sample. Superconductors exhibit non-zero electrical resistance under
circumstances where phase slips occur at a finite rate. For one-dimensional
superconductors or Josephson junctions, phase slips can occur at isolated
points in space-time. Phase slip rates may be controlled by thermal activation
over a free-energy barrier, or in some circumstances, at low temperatures, by
quantum tunneling through a barrier. We present an overview of several
phenomena involving vortices that have direct implications for the electrical
resistance of superconductors, including the Berezinskii-Kosterlitz-Thouless
transition for vortex-proliferation in thin films, and the effects of vortex
pinning in bulk type II superconductors on the non-linear resistivity of these
materials in an applied magnetic field. We discuss how quantum fluctuations can
cause phase slips and review the non-trivial role of dissipation on such
fluctuations. We present a basic picture of the superconductor-to-insulator
quantum phase transitions in films, wires, and Josephson junctions. We point
out related problems in superfluid helium films and systems of ultra-cold
trapped atoms. While our emphasis is on theoretical concepts, we also briefly
describe experimental results, and we underline some of the open questions.Comment: Chapter to appear in "Bardeen, Cooper and Schrieffer: 50 Years,"
edited by Leon N. Cooper and Dmitri Feldman, to be published by World
Scientific Pres
Relaxation and Coarsening Dynamics in Superconducting Arrays
We investigate the nonequilibrium coarsening dynamics in two-dimensional
overdamped superconducting arrays under zero external current, where ohmic
dissipation occurs on junctions between superconducting islands through uniform
resistance. The nonequilibrium relaxation of the unfrustrated array and also of
the fully frustrated array, quenched to low temperature ordered states or
quasi-ordered ones, is dominated by characteristic features of coarsening
processes via decay of point and line defects, respectively. In the case of
unfrustrated arrays, it is argued that due to finiteness of the friction
constant for a vortex (in the limit of large spatial extent of the vortex), the
typical length scale grows as accompanied by the number
of point vortices decaying as . This is in contrast with the
case that dominant dissipation occurs between each island and the substrate,
where the friction constant diverges logarithmically and the length scale
exhibits diffusive growth with a logarithmic correction term. We perform
extensive numerical simulations, to obtain results in reasonable agreement. In
the case of fully frustrated arrays, the domain growth of Ising-like chiral
order exhibits the low-temperature behavior , with the
growth exponent apparently showing a strong temperature dependence in
the low-temperature limit.Comment: 9 pages, 5 figures, to be published in Phys. Rev.
Fluctuation induced vortex pattern and its disordering in the fully frustrated XY model on a dice lattice
A highly degenerate family of states [proposed in PRB 63, 134503 (2001)] is
proven to really minimize the Hamiltonian of the fully frustrated XY model on a
dice lattice. The harmonic fluctuations are shown to be no consequence for the
removal of the accidental degeneracy of these states, so a particular vortex
pattern can be stabilized only by the anharmonic fluctuations. The structure of
this pattern is found and the temperature of its disordering due to the
proliferation of domain walls is estimated. The extreme smallness of the
fluctuations induced free energy of domain walls leads to the anomalous
prominence of the finite-size effects, which prevent the observation of
vortex-pattern ordering in numerical simulations. In such a situation the loss
of phase coherence may be related to the dissociation of fractional vortices
with topological charges 1/8. In a physical situation the magnetic interaction
of currents in a Josephson junction array will be a more important source for
the stabilization of a particular vortex pattern than the anharmonic
fluctuations.Comment: 20 pages, 7 figure
Structure of the superconducting state in a fully frustrated wire network with dice lattice geometry
The superconducting state in a fully frustrated wire network with the dice
lattice geometry is investigated in the vicinity of the transition temperature.
Using Abrikosov's variational procedure, we write the Ginzburg-Landau free
energy functional projected on its unstable supspace as an effective model on
the triangular lattice of sixfold coordinated sites. For this latter model, we
obtain a large class of degenerate equilibrium configurations in one to one
correspondence with those previously constructed for the pure XY model on the
maximally frustrated dice lattice. The entropy of these states is proportional
to the linear size of the system. Finally we show that magnetic interactions
between currents provide a degeneracy lifting mechanism.Comment: The final version (as published in Phys. Rev. B). Substantial
corrections have been made to Sec.
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