Transport and relaxation properties in anisotropic superconductors

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Bahlouli, Hocine

Contributors dc:contributor

• Leggett, Anthony J.

• transport properties
• relaxation properties
• anisotropic superconductors
• heavy fermion metals
• nuclear spin relaxation time

Statement dc:rights

• 1988 Hocine Bahlouli

Language dc:language

en

Identifier

1854051

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/23924