The T dependence of spin-lattice relaxation time ${\mathit{T}}_1$ at the apical O and the Tl sites has been found to scale to that of the Cu site in ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{CuO}}_{\mathit{y}}$ (${\mathit{T}}_{\mathit{c}}$=85 K), indicating the existence of the supertransferred hyperfine coupling between the Cu and the Tl sites via the apical O. This fact is also direct evidence for the transferred spin polarization at the apical O site, and the covalent bonding between the Cu 3${\mathit{d}}_{3\mathit{z}}^2$-${\mathit{r}}^2$ and the apical O 2s states. Based on the scaled ${\mathit{T}}_1$ behavior, we suggest that intrasite charge transfer takes place from Cu 3${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$ to Cu 3${\mathit{d}}_{3\mathit{z}}^2$-${\mathit{r}}^2$ states.

• Received 26 April 1993

DOI:https://doi.org/10.1103/PhysRevB.48.6593