Effect of carrier distribution on superconducting characteristics of the multilayered high-Tccuprate(Cu0.6C0.4)Ba2Ca3Cu4O12+y:63Cu−NMRstudy

Abstract

We report Cu-NMR studies of the multilayered high-${T}_{c}$ cuprate $({\mathrm{Cu}}_{0.6}{\mathrm{C}}_{0.4}){\mathrm{Ba}}_{2}{\mathrm{Ca}}_{3}{\mathrm{Cu}}_{4}{\mathrm{O}}_{12+y}$ (Cu1234) with ${T}_{c}=117$ K. In the normal state, the Knight shift (K) and the nuclear spin-lattice relaxation rate ${(1/T}_{1})$ of ${}^{63}\mathrm{Cu}$ give evidence that the inner ${\mathrm{CuO}}_{2}$ planes (IP) are underdoped, whereas the outer ones (OP) are heavily overdoped. In the superconducting (SC) state, both K and ${1/T}_{1}$ decrease markedly below ${T}_{c}=117$ K in the IP, whereas in the OP they decrease moderately below ${T}_{c}=117$ K, but markedly below ${T}_{c2}=60$ K. The unusual NMR results in the OP reveal that the SC gap does not fully develop down to ${T}_{c2}=60$ K. From comparison with a conventional d-wave model, it is shown that the SC gap in the OP increases linearly below ${T}_{c}$ and follows the mean-field type of T dependence below ${T}_{c2}.$ We propose that these dissimilarities are caused by the large difference of doping levels between the IP and the OP. The bulk SC transition at ${T}_{c}=117$ K is considered to be triggered by the underdoped IP in Cu1234.