Anomalous Temperature Dependence of Cu Nuclear Spin-Lattice Relaxation in YBa2Cu3O6.91

Abstract
An anomalous temperature dependence of Cu nuclear spin-lattice relaxation time T 1 has been observed for both the Cu1 chain and Cu2 plane sites of YBa 2 Cu 3 O 6.91 ( T c =90 K) and discussed in connection with spin fluctuations and an anisotropic energy gap which nucleates in the vicinity of Cu2 nuclei.