205Tl nuclear spin lattice relaxation in the one layer (Tl 2Ba 2CuO 6), two layer (Tl 2CaBa 2Cu 2O 8) and three layer (Tl 2Ca 2Ba 2CuO 10 ) high-T c superconductors

Abstract

We report on the comparison of the 205Tl nuclear spin lattice relaxation rate 1/ T 1 versus temperature below and above T c in the three title compounds. Although T c varies significantly for the three compounds, their relaxation rates 1/ T 1 behave almost identical above and below T c. In the regime T > T c non-Korringa behaviour is observed, resembling the 63Cu relaxation in the CuO 2 layer (Cu(2)) of YBa 2Cu 3O 7, whereas for T< T c the relaxation rate decreases rapidly with decreasing temperature due to a gap opening in the magnetic excitation. However, Korringa behaviour is observed for a Tl defect located between the CuO 2 layers in Tl 2CaBa 2Cu 2O 8.