674 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
Optical conductivity near finite-wavelength quantum criticality
We study the optical conductivity sigma(Omega) of an electron system near a
quantum-critical point with finite-wavelength ordering. sigma(Omega) vanishes
in clean Galilean-invariant systems, unless electrons are coupled to dynamical
collective modes, which dissipate the current. This coupling introduces a
nonuniversal energy scale. Depending on the parameters of each specific system,
a variety of responses arise near criticality: scaling peaks at a temperature-
and doping-dependent frequency, peaks at a fixed frequency, or no peaks to be
associated with criticality. Therefore the lack of scaling in the far-infrared
conductivity in cuprates does not necessarily call for new concepts of quantum
criticality.Comment: 4 pages, 4 figures; version as publishe
Domain Walls in Superfluid 3He-B
We consider domain walls between regions of superfluid 3He-B in which one
component of the order parameter has the opposite sign in the two regions far
from one another. We report calculations of the order parameter profile and the
free energy for two types of domain wall, and discuss how these structures are
relevant to superfluid 3He confined between two surfaces.Comment: 6 pages with 3 figures. Conference proceedings of QSF 2004, Trento,
Ital
Comment on "c-axis Josephson tunneling in -wave superconductors''
This comment points out that the recent paper by Maki and Haas [Phys. Rev. B
{\bf 67}, 020510 (2003)] is completely wrong.Comment: 1 page, submittted to Phys. Rev.
Theory of Coherent -Axis Josephson Tunneling between Layered Superconductors
We calculate exactly the Josephson current for -axis coherent tunneling
between two layered superconductors, each with internal coherent tight-binding
intra- and interlayer quasiparticle dispersions. Our results also apply when
one or both of the superconductors is a bulk material, and include the usually
neglected effects of surface states. For weak tunneling, our results reduce to
our previous results derived using the tunneling Hamiltonian. Our results are
also correct for strong tunneling. However, the -axis tunneling results of
Tanaka and Kashiwaya are shown to be incorrect in any limit. In addition, we
consider the -axis coherent critical current between two identical layered
superconductors twisted an angle about the -axis with respect to
each other. Regardless of the order parameter symmetry, our coherent tunneling
results using a tight-binding intralayer quasiparticle dispersion are
inconsistent with the recent -axis twist bicrystal
BiSrCaCuO twist junction experiments of Li {\it et
al.}Comment: 11 pages, 13 figures, submitted to Physical Review
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