4 research outputs found
Anomalous Behavior of the Upper Critical Field in Extreme Type-II Superconductors at Low Temperatures
We present a detailed numerical calculation of the upper critical field
for a bulk extreme type-II superconductor. Particular emphasis is
placed on the high-field, low-temperature regime of the HT-phase diagram. In
this regime it is necessary to go beyond the standard semi-classical theory and
include the effects of Landau quantization of the electronic motion on the
superconducting state. The presence of Landau level quantization induces an
upward curvature in at of for those
superconducting systems in which the slope of at is 0.2 Tesla/Kelvin. We construct a simple analytical model that can account for
this behavior based on the renormalization of the BCS coupling constant by the
off-diagonal pairing of electrons on Landau levels.Comment: 13 pages, Revtex, 3 ps figures, to appear in Physica
Density of states of a type-II superconductor in a high magnetic field: Impurity effects
We have calculated the density of states of a dirty but
homogeneous superconductor in a high magnetic field. We assume a dilute
concentration of scalar impurities and find how behaves as one
crosses from the weak scattering to the strong scattering limit. At low
energies, for small values of the impurity
concentration and scattering strength. When the disorder becomes stronger than
some critical value, a finite density of states is created at the Fermi
surface. These results are a consequence of the gapless nature of the
quasiparticle excitation spectrum in a high magnetic field.Comment: 20 pages in RevTeX, 4 figures, to appear in Phys. Rev. B (July 1,
1997
Superconductivity in High Magnetic Field:Excitation Spectrum and Tunneling Properties
The quasiparticle excitation spectrum of a type-II superconductor placed in
high magnetic field is shown to be gapless. The gap turns to zero at the points
in the MBZ which are in correspondence with the vortex lattice in real space.
When the field decreases below certain critical value, branch crossing occur
and gaps starts opening up at the Fermi surface.The strong dispersion around
gapless points leads to algebraic temperature dependence in the thermodynamic
functions and the algebraic voltage dependence in the tunneling conductance
between the microscope tip and superconductor in an STM experiment.Comment: 16 pages+$figures (on request), REVTE