Superconducting and magnetic characteristics in the multilayered high-T_c cuprates TlBa₂Ca₂Cu₃O_10-y with T_c>130 K probed by Cu and Tl NMR: High value for T_c

We report ⁶³Cu and ²⁰⁵Tl nuclear magnetic resonance (NMR) measurements on trilayered high-T_c compounds TlBa₂Ca₂Cu₃O_10-y (Tl-1223) that were synthesized at a high pressure and exhibits a high value of superconducting (SC) transition temperature T_c > 130 K. In the SC state, the nuclear spin-lattice relaxation rate 1/T1 reveals a T³ behavior below T_c, followed by a T₁T=const behavior at very low temperatures. The results are accounted for by the d-wave pairing model where the presence of the residual density of the states N_res(E_F) is incorporated at the Fermi level to be consistent with the experiments. The important finding is that the size [in N_res (E_F)] is much smaller for the present compounds of Tl-1223 with T_c > 130 K than for the previous Tl-2223. Correspondingly, it is shown that an NMR intensity at a satellite peak in the Tl-NMR spectrum, which originates from a possible substitution of Tl for Ca, is much smaller for the former than for the latter. The synthesis technique at a high pressure is found to be a good way to remove such a crystal imperfection due to Tl/Ca intersubstitution. We have demonstrated from a microscopic point of view that as a result of decreasing the degree of disorder effect, the T_c in Tl-1223 has revealed a value higher than 130 K.