22 research outputs found
Disappearance of Ensemble-Averaged Josephson Current in Dirty SNS Junctions of d-wave Superconductors
We discuss the Josephson current in superconductor / dirty normal conductor /
superconductor junctions, where the superconductors have pairing
symmetry. The low-temperature behavior of the Josephson current depends on the
orientation angle between the crystalline axis and the normal of the junction
interface. We show that the ensemble-averaged Josephson current vanishes when
the orientation angle is and the normal conductor is in the diffusive
transport regime. The -wave pairing symmetry is responsible for
this fact.Comment: 8 pages, 5 figure
Influence of thermal fluctuations on quantum phase transitions in one-dimensional disordered systems: Charge density waves and Luttinger liquids
The low temperature phase diagram of 1D weakly disordered quantum systems
like charge or spin density waves and Luttinger liquids is studied by a
\emph{full finite temperature} renormalization group (RG) calculation. For
vanishing quantum fluctuations this approach is amended by an \emph{exact}
solution in the case of strong disorder and by a mapping onto the \emph{Burgers
equation with noise} in the case of weak disorder, respectively. At \emph{zero}
temperature we reproduce the quantum phase transition between a pinned
(localized) and an unpinned (delocalized) phase for weak and strong quantum
fluctuations, respectively, as found previously by Fukuyama or Giamarchi and
Schulz.
At \emph{finite} temperatures the localization transition is suppressed: the
random potential is wiped out by thermal fluctuations on length scales larger
than the thermal de Broglie wave length of the phason excitations. The
existence of a zero temperature transition is reflected in a rich cross-over
phase diagram of the correlation functions. In particular we find four
different scaling regions: a \emph{classical disordered}, a \emph{quantum
disordered}, a \emph{quantum critical} and a \emph{thermal} region. The results
can be transferred directly to the discussion of the influence of disorder in
superfluids. Finally we extend the RG calculation to the treatment of a
commensurate lattice potential. Applications to related systems are discussed
as well.Comment: 19 pages, 7 figure
The reactions near threshold
A preliminary calculation of the total cross sections for
the reactions , , ,
and was carried out for the incident proton
energy range MeV. This calculation was done in the
framework of a model based on a version of the standard
effective chiral Lagrangian, for which only three- and four-pion
diagrams were taken into account together with diagrams containing
two two-pion vertices. The invariant amplitudes were calculated
to the threshold approximation. It was shown that for a reliable
description of the reactions under consideration it is necessary
to take into account the mechanism too. The final state
interaction of the nucleons was also considered. Results of the
calculation are compared with available experimental data
Cross sections of low-energy neutron scattering on even Ru and Pd isotopes and the generalized optical model
Low-energy neutron interaction with even-even nuclei and coupled channel optical model
We revised a description of low-energy neutron cross section
data for even-even spherical nuclei in terms of the coupled channel optical
model (CCOM). It is shown that two-phonon version of this model allows
to obtain a unified description of these data assuming slight changes
of nuclear diffuseness parameter for magic and near-magic nuclei.
Neutron strength functions and scattering lengths for even-even
spherical nuclei are also calculated using the same model. Results
of these calculations are in a good agreement with experimental
data. -systematics of inelastic neutron scattering on even-even
nuclei is proposed. This systematics combined with CCOM calculations
of neutron cross sections presents an additional method for finding
nuclei with semimagic numbers of nucleons