571 research outputs found

### Comment on "Magnetic response of Disordered Metallic Rings: Large Contributions of Far Levels"

Comment on cond-mat/0205390; PRL 90, 026805 (2003

### Critical Current in the High-T_c Glass model

The high-T_c glass model can be combined with the repulsive tt'--Hubbard
model as microscopic description of the striped domains found in the high-T_c
materials. In this picture the finite Hubbard clusters are the origin of the
d-wave pairing. In this paper we show, that the glass model can also explain
the critical currents usually observed in the high-T_c materials. We use two
different approaches to calculate the critical current densities of the
high-T_c glass model. Both lead to a strongly anisotropic critical current.
Finally we give an explanation, why we expect nonetheless a nearly perfect
isotropic critical current in the high-T_c superconductors.Comment: 8 pages with 5 eps-figures, LaTeX using RevTeX, accepted by
Int.J.Mod.Phys.

### Decoherence without dissipation?

In a recent article, Ford, Lewis and O'Connell (PRA 64, 032101 (2001))
discuss a thought experiment in which a Brownian particle is subjected to a
double-slit measurement. Analyzing the decay of the emerging interference
pattern, they derive a decoherence rate that is much faster than previous
results and even persists in the limit of vanishing dissipation. This result is
based on the definition of a certain attenuation factor, which they analyze for
short times. In this note, we point out that this attenuation factor captures
the physics of decoherence only for times larger than a certain time t_mix,
which is the time it takes until the two emerging wave packets begin to
overlap. Therefore, the strategy of Ford et al of extracting the decoherence
time from the regime t < t_mix is in our opinion not meaningful. If one
analyzes the attenuation factor for t > t_mix, one recovers familiar behaviour
for the decoherence time; in particular, no decoherence is seen in the absence
of dissipation. The latter conclusion is confirmed with a simple calculation of
the off-diagonal elements of the reduced density matrix.Comment: 8 pages, 4 figure

### Collective modes and electromagnetic response of a chiral superconductor

Motivated by the recent controversy surrounding the Kerr effect measurements
in strontium ruthenate \cite{xia:167002}, we examine the electromagnetic
response of a clean chiral p-wave superconductor. When the contributions of the
collective modes are accounted for, the Hall response in a clean chiral
superconductor is smaller by several orders of magnitude than previous
theoretical predictions and is too small to explain the experiment. We also
uncover some unusual features of the collective modes of a chiral
superconductor, namely, that they are not purely longitudinal and couple to
external transverse fields.Comment: 8 page

### Quantum Master Equation of Particle in Gas Environment

The evolution of the reduced density operator $\rho$ of Brownian particle is
discussed in single collision approach valid typically in low density gas
environments. This is the first succesful derivation of quantum friction caused
by {\it local} environmental interactions. We derive a Lindblad master equation
for $\rho$, whose generators are calculated from differential cross section of
a single collision between Brownian and gas particles, respectively. The
existence of thermal equilibrium for $\rho$ is proved. Master equations
proposed earlier are shown to be particular cases of our one.Comment: 6 pages PlainTeX, 23-March-199

### Subgap features due to quasiparticle tunneling in quantum dots coupled to superconducting leads

We present a microscopic theory of transport through quantum dot set-ups
coupled to superconducting leads. We derive a master equation for the reduced
density matrix to lowest order in the tunneling Hamiltonian and focus on
quasiparticle tunneling. For high enough temperatures transport occurs in the
subgap region due to thermally excited quasiparticles, which can be used to
observe excited states of the system for low bias voltages. On the example of a
double quantum dot we show how subgap transport spectroscopy can be done.
Moreover, we use the single level quantum dot coupled to a normal and a
superconducting lead to give a possible explanation for the subgap features
observed in the experiments published in Appl. Phys. Lett. 95, 192103 (2009).Comment: 18 pages, 20 figures, revised according to published versio

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