Effect of disorder on the NMR relaxation rate in two-band superconductors

TL;DR

This paper investigates how nonmagnetic impurities affect the NMR relaxation rate in two-band superconductors, revealing that disorder suppresses the Hebel-Slichter peak at low impurity levels but restores single-band behavior at high impurity levels.

Contribution

It provides a detailed analysis of impurity effects on NMR relaxation in two-band superconductors, highlighting the transition from suppressed to restored coherence peaks with increasing disorder.

Findings

Disorder suppresses the Hebel-Slichter peak in MgB2-like superconductors.

Strong impurity scattering leads to nearly equal gap functions in both bands.

Single-band behavior with a coherence peak reappears at high impurity levels.

Abstract

We calculate the effect of nonmagnetic impurity scattering on the spin-lattice relaxation rate in two-band superconductors with the s-wave pairing symmetry. It is found that for the interaction parameters appropriate for MgB2 the Hebel-Slichter peak is suppressed by disorder in the limit of small interband impurity scattering rate. In the limit of strong impurity scattering, when the gap functions in the two bands become nearly equal, the single-band behavior is recovered with a well-defined coherence peak just below the transition temperature.