⁶³Cu NMR study of heavily doped superconductor TlSr₂CaCu₂O_7-y

The ⁶³Cu Knight shifts have been measured for the heavily doped high-T_c superconductors TlSr₂CaCu₂O_7-y, with T_c = 64 and 45 K. The spin part of the shift, K_s, is almost T-independent in the normal state and increases with decreasin g T_c. From the analysis of the anisotropy in K_s in both compounds, the transferred hyperfine field from the nearest-neighbor Cu spins has been deduced to be larger than that in YBa₂Cu₃O₇, similar to the results for Tl₂Ba₂CuO_6+y. A systemat ic correlation has been found in the heavily doped superconductors that the spin susceptibility and the nuclear quadrupole frequency increase with decreasing T_c, while 1/T₁T is suppressed, as reported previously.