2 research outputs found
Coulomb suppression of NMR coherence peak in fullerene superconductors
The suppressed NMR coherence peak in the fullerene superconductors is
explained in terms of the dampings in the superconducting state induced by the
Coulomb interaction between conduction electrons. The Coulomb interaction,
modelled in terms of the onsite Hubbard repulsion, is incorporated into the
Eliashberg theory of superconductivity with its frequency dependence considered
self-consistently at all temperatures. The vertex correction is also included
via the method of Nambu. The frequency dependent Coulomb interaction induces
the substantial dampings in the superconducting state and, consequently,
suppresses the anticipated NMR coherence peak of fullerene superconductors as
found experimentally.Comment: 4 pages, Revtex, and 2 figures. Revised and final version to appear
in Phys. Rev. Lett. (1998
Finite-Band-width Effects on the Transition Temperature and NMR Relaxation Rate of Impure Superconductors
We study the thermodynamic properties of impure superconductors by explicitly
taking into consideration the finiteness of electronic bandwidths within the
phonon-mediated Eliashberg formalism. For a finite electronic bandwidth, the
superconducting transition temperature, , is suppressed by nonmagnetic
impurity scatterings. This is a consequence of a reduction in the effective
electron-phonon coupling, . The reduced is
reflected in the observation that the coherence peak in , where
is the nuclear spin-lattice relaxation time and is the temperature,
is enhanced by impurity scatterings for a finite bandwidth. Calculations are
presented for and as bandwidths and impurity scattering rates
are varied. Implications for doped C superconductors are discussed in
connection with and measurements.Comment: 10 pages. REVTeX. 5 postscript figures. Scheduled to be published in
Physical Review B, March 1. The previous submission is revised and two
figures are adde