205Tl Knight and chemical shift in the high- Tc superconductors Tl 2Ba 2CuO 6, Tl 2CaBa 2Cu 2O 8 and Tl 2Ca 2Ba 2Cu 3O 10

Abstract

We report on the 205Tl NMR (nuclear magnetic resonance) spectra of the title compounds below and above the superconducting transition temperature T c. The TlO layer NMR spectra are dominated by chemical shifts corresponding to Tl 3+ with a smaller additional positive Knight shift, whereas a “defect line” of Tl replacing Ca in the two and three layer compounds exhibits a large negative Knight shift, which is attributed to O-holes in the CuO 2 layers.