Small $T_1^{-1}$ coherence peak near $T_c$ in unconventional superconductors

TL;DR

This paper shows that unconventional superconductors can exhibit a small coherence peak in the nuclear spin relaxation rate near T_c, challenging the belief that such peaks are exclusive to conventional s-wave superconductors.

Contribution

It demonstrates that all unconventional superconductors within BCS weak-coupling theory should display a small coherence peak near T_c, explaining its rarity due to impurity effects.

Findings

Unconventional superconductors show a small T_1^{-1} peak near T_c.

Peak height is typically 3-15% above normal state T_1^{-1}.

Impurities largely suppress the observation of this peak.

Abstract

It is usually believed that a coherence peak just below T$_{c}$ in the nuclear spin lattice relaxation rate T$_{1}^{-1}$ in superconducting materials is a signature of conventional s-wave pairing. In this paper we demonstrate that any unconventional superconductor obeying BCS pure-case weak-coupling theory should show a small T$_{1}^{-1}$ coherence peak near T$_{c}$, generally with a height between 3 and 15 percent greater than the normal state T$_{1}^{-1}$ at T$_{c}$. It is largely due to impurity effects that this peak has not commonly been observed.