Models for quadrupole-resonance centers of copper nuclei in YBa2Cu3O7-δ
Eremin M. V. , Graboi I. E., Egorov A. V., Naletov V. V. , Tagirov M. S., Teplov M. A.
The spin-spin relaxation and spin-lattice relaxation of 63Cu nuclei have been studied at a frequency of 31.5 MHz at temperatures of 120 К and 4.2 К in polycrystalline samples of YBa2Cu307_(5 with δ = 0.11-0.43. A sharp change in the relaxation rates is observed at δ — 0.3. Some models for the electronic structure of Cu (1) and Cu (2) centers are proposed on the basis of an analysis of the experimental data and calculations of the electric-field gradients.