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Measurements of the relaxation of quasiparticle branch imbalance in superconductors

Measurements of the relaxation of quasiparticle branch imbalance in superconductors An imbalanceQ in the quasiparticle populations of thek>k F andk<k F branches of a superconductor may be generated by the injection of a current through a tunnel barrier. This imbalance relaxes with a characteristic timeτ Q . The steady-state value ofQ gives rise to a quasiparticle potentialV that differs from the pair chemical potential, and which may be measured by a second tunnel junction. Tinkham's theory of these effects is briefly reviewed. Detailed experimental results are presented for tin. Most of the data are for injection voltages much greater than the energy gapΔ(T). Close to the transition temperatureT c ,Q relaxes by inelastic phonon scattering, andτ Q ph =(1.0±0.2)×10−10 Δ(0)/Δ(T) sec. This time is about one-half that estimated by Tinkham. At temperatures somewhat belowT c, elastic scattering also contributes to theQ relaxation, provided the superconducting energy gap is anisotropic. With a size-effect-limited mean free path of about 2800 Å, we findτ Q el ≈1.4×10−10 sec forT/T c <0.6, a value that is also in good agreement with Tinkham's theory. In a sample with a mean free path of 420 Å, and a greatly reduced anisotropy,τ Q el was increased to about 10−9 sec. Data were also taken for injection voltages close toΔ(T)/e. The degree of imbalance per unit injection current was greatly reduced, as predicted by the theory. Preliminary measurements were made on lead. At 4.2K (T/T c =0.58) the characteristic time was about 3×10−12 sec. The quasiparticle potential apparently increased steadily as the temperature was lowered, probably indicating that the characteristic time also increased. This result is not well understood. However, it is possible that recombination processes play a role in theQ relaxation in lead. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Low Temperature Physics Springer Journals

Measurements of the relaxation of quasiparticle branch imbalance in superconductors

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Publisher
Springer Journals
Copyright
Copyright
Subject
Physics; Condensed Matter Physics; Characterization and Evaluation of Materials; Magnetism, Magnetic Materials
ISSN
0022-2291
eISSN
1573-7357
DOI
10.1007/BF00654623
Publisher site
See Article on Publisher Site

Abstract

An imbalanceQ in the quasiparticle populations of thek>k F andk<k F branches of a superconductor may be generated by the injection of a current through a tunnel barrier. This imbalance relaxes with a characteristic timeτ Q . The steady-state value ofQ gives rise to a quasiparticle potentialV that differs from the pair chemical potential, and which may be measured by a second tunnel junction. Tinkham's theory of these effects is briefly reviewed. Detailed experimental results are presented for tin. Most of the data are for injection voltages much greater than the energy gapΔ(T). Close to the transition temperatureT c ,Q relaxes by inelastic phonon scattering, andτ Q ph =(1.0±0.2)×10−10 Δ(0)/Δ(T) sec. This time is about one-half that estimated by Tinkham. At temperatures somewhat belowT c, elastic scattering also contributes to theQ relaxation, provided the superconducting energy gap is anisotropic. With a size-effect-limited mean free path of about 2800 Å, we findτ Q el ≈1.4×10−10 sec forT/T c <0.6, a value that is also in good agreement with Tinkham's theory. In a sample with a mean free path of 420 Å, and a greatly reduced anisotropy,τ Q el was increased to about 10−9 sec. Data were also taken for injection voltages close toΔ(T)/e. The degree of imbalance per unit injection current was greatly reduced, as predicted by the theory. Preliminary measurements were made on lead. At 4.2K (T/T c =0.58) the characteristic time was about 3×10−12 sec. The quasiparticle potential apparently increased steadily as the temperature was lowered, probably indicating that the characteristic time also increased. This result is not well understood. However, it is possible that recombination processes play a role in theQ relaxation in lead.

Journal

Journal of Low Temperature Physics – Springer Journals

Published: Nov 2, 2004

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