EFFECTS OF IMPURITY VERTEX CORRECTION ON THE NMR COHERENCE PEAK IN S-WAVE SUPERCONDUCTORS

We study the effects of nonmagnetic impurity vertex correction on nucl ear spin-lattice relaxation rate 1/T-1 of conventional s-wave supercon ductors within the Eliashberg formalism. We obtain, with a self-consis tent t-matrix treatment of impurity scatterings, the expressions for i mpurity vertex function and nuclear spin-lattice relaxation rate. The 1/T-1 is evaluated with a simple approximation on angular average, and found to agree in clean limit with the previous result that 1/(T1T) r emains unrenormalized under the impurity vertex correction. As dirtine ss is increased, on the other hand, the coherence peak in 1/(T1T) is f ound to increase due to the impurity vertex correction. This result is discussed in connection with the experimental observations on convent ional superconductors.