1 research outputs found
Hump Structure below Tc in the thermal conductivity of MgB2 superconductor
A reasonable cause of absence of hump structure in thermal conductivity of
MgB2 below the superconducting transition temperature (Tc) lies in the
appearance of multigap structure. The gaps of lower magnitude can be suppressed
by defects so that this system becomes effectively a single gap superconductor.
When such a situation is created, it is hoped that thermal conductivity will
show hump below Tc. Proceeding along these lines, a sample of MgB2 with a
relatively higher residual resistivity (33.3 mili-Ohm-cm)has been found to show
a hump structure below Tc. The actual electronic thermal conductivity kel of
this sample is less than that expected from the Wiedeman- Franz law by more
than a factor of 2.6 in the considered temperature range. Modifying the
Wiedeman- Franz law for the electronic contribution by replacing the Lorenz
number by an effective Lorenz number Leff (L0) we have obtained two sets of
kel, namely those with Leff = 0.1L0 and 0.2L0. Corresponding to these two sets
of kel, two sets of the phonon thermal conductivity kph are obtained. kph has
been analyzed in terms of an extended Bardeen- Rickayzen- Tewordt theory. The
main result of this analysis is that the hump structure corresponds to a gap
ratio of 3.5, and that large electron-point defect scattering is the main
source of drastic reduction of the electronic thermal conductivity from that
given by the usual Wiedeman- Franz law.Comment: 18 pages of Text + Figs: comments welcome
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