Transport and relaxation properties in anisotropic superconductors
Bahlouli, Hocine
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https://hdl.handle.net/2142/23924
Description
Title
Transport and relaxation properties in anisotropic superconductors
Author(s)
Bahlouli, Hocine
Issue Date
1988
Doctoral Committee Chair(s)
Leggett, Anthony J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
transport properties
relaxation properties
anisotropic superconductors
heavy fermion metals
nuclear spin relaxation time
Language
en
Abstract
The nature of the superconducting state formed in some of the heavy fermion (HF)
metals remains a subject of debate. In this thesis we give a theoretical analysis of some
experiments which help to decide the issue. We give a detailed calculation of the nuclear
spin relaxation time (T1 ) in anisotropic superconductors. It is shown that besides the
power-low like behavior at intermediate temperatures, a Korringa-like behavior shows up
at very low temperatures if resonant non-magnetic impurity scattering effect is included
self-consistently in the calculations. The magnetic field effect on T1 is also studied, and we
found that for high enough fields a new process, the pair creation process, will dominate
the relaxation which results in a Korringa-like behavior. More importantly we found that
due to the competition between the usual spin-flip contribution and the anomalous paircreation
contribution at very low temperatures, the nuclear-spin relaxation time develops
a minimum which scales with the applied magnetic field. Besides, we have studied the
possible orientation dependence of T1 if the dipolar interaction gives the dominant contribution.
We evaluate our results explicitly using some of the allowed group theoretical
states in HF superconductors.
Heavy fermion metals are peculiar in many respects, two of which are of interest
to us
1. The normal state thermopower coefficient is large, signaling the presence of a. substancial
particle-hole asymmetry in the normal density of states.
2. transport properties seem to be dominated by non-magnetic impurity scattering close
to the resonant limit.
In the superconducting state, the second aspect results in a particle-hole asymmetry in the
scattering amplitude which gives rise to an anomalously large thermoelectric coefficient
if the normal state scattering phase shift is different from 1r /2. The asymmetry which is
already present in the normal state, means that the contribution of the gap relaxation
to the sound attenuation is substantially enhanced in these systems. Finally, we tried to
suggest some further possible experimental means of probing the anisotropy of the gap
by applying a magnetic field or a supercurrent flow to our superconductor and varying its
direction.
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