Spin dynamics at oxygen sites in YBa2Cu3O7

Abstract

We report NMR measurements of the nuclear relaxation rate at all copper and oxygen sites in magnetically aligned powder samples of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. Comparison of the oxygen and copper relaxation reveals a characteristic temperature greater than $T_c$. The copper relaxation rate is enhanced by antiferromagnetic copper spin fluctuations which are undiminished in the superconducting state. The absence of a coherence peak indicates that the superconductive pairing is not of the conventional BCS type.