Anomalous behavior of nuclear spin-lattice relaxation rates in YBa2Cu3O7 below Tc

Abstract
The authors have measured the change in the anisotropy of the NMR spin-lattice relaxation rates for Cu63(2), O17(2,3), and Y89 between the normal and superconducting states of YBa2 Cu3 O7. These results cannot be explained by a straightforward extension to T<Tc of current theories, such as the theory of Millis, Monien, and Pines of normal-state NMR relaxation.