Conduction electron spin resonance due to exchange and spin‐orbit scatterings by silute impurities in superconductors

Abstract

AbstractA simple theory is developed to calculate the transverse relaxation time, T2, of the spin of the conduction electrons in a slightly dirty superconductor. Two scattering mechanisms are considered: exchange interaction between the conduction electron spin and the impurity spin (for magnetic impurities only), and spin‐orbit interaction of the conduction electron around the impurity (for all kinds of impurities). As in Maki's Green‐function theory, a sudden increase (decrease) of T with respect to its value in the normal state, for the exchange (spin‐orbit) mechanism is obtained immediately below the critical temperature T0 which separates the normal and superconducting states. For vanishing temperature, T vanishes in both the cases. The asymptotic behaviours for T → T0 and T→0 are calculated. In the spin‐orbit case, T goes to zero, for T→0, surprisingly slowly. In order to exhibit the great sensitivity of T2 on the density of electronic states, it is re‐calculated, for both mechanisms, using an heuristic density of states which is physically reasonable but different from the BCS one. The height and width of the density of states modify not only the proportionality coefficients of T vs. T, but even the exponents in the limit T→0.