Nuclear Spin-Lattice Relaxation in Impure Superconducting Indium
The measured nuclear spin-lattice relaxation time T 1 in type I superconductors is always found to be greater than that calculated according to the simplest form of the BCS theory (see e. g., Ref. 1). This disagreement has been generally attributed to the singular behavior at the gap edge of the BCS density of excited quasiparticle states. In essence the singularity makes too many states available for thermal excitation, so that the calculated relaxation is too rapid. Any effect in real superconductors which broadens or redistributes excited states over a region in the neighborhood of the gap energy will thus tend to lengthen the nuclear relaxation time, and measurements of T 1 as a function of experimental conditions can be used to elucidate the nature of such broadening mechanisms.
KeywordsResidual Resistivity Ratio Crystal Momentum Nuclear Relaxation Time Calculated Relaxation InPb Alloy
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