EPR study of the high-TCsuperconductor YBa2Cu3O7−δ

Abstract
EPR spectra of superconducting YBa2Cu3O7-δ and insulating Y2BaCuO5 have been examined. The intensity of Cu2+ ions in YBa2Cu3O7-δ is about 1/3000 of that in Y2BaCuO5 at room temperature. Owing to the Meissner effect in the superconducting state, the EPR signal of Cu2+ ions in YBa2Cu3O7-δ disappears; moreover the EPR signal of DPPH deposited on the YBa2Cu3O7-δ specimen is shifted. An additional EPR line is found for YBa2(Cu2.94Cr0.06)O7-δ at temperatures below 113K; this can be related to the phenomenon of superconductivity.