Nuclear Spin-Lattice Relaxation of ^63,65Cu at the Cu(2) Sites of the High T_c Superconductor YBa₂Cu₃O_7−δ

Abstract

Nuclear spin-lattice relaxation times T₁ of ⁶³Cu and ⁶⁵Cu in the Cu(2) sites of the high T_c superconductor YBa₂Cu₃O_7−δ (δ\simeq0.1, T_c=91 K) have been measured for the wide temperature range between 2.2 K and 300 K. The temperature dependence of 1⁄T₁ in the normal state has been found to be the one unexpected for simple metals. The influences of antiferromagnetic spin fluctuations in the d-p bands in the Cu(2)–O layers are discussed. The temperature dependence of 1⁄T₁ below T_c has also been found to be the one which is not expected for isotropic BCS superconductors. The power-law like temperature dependence of 1⁄T₁ without any enhancement just below T_c has been observed between 40 K and 91 K.