NMR study of local hole distribution, spin fluctuation and superconductivity in Tl 2Ba 2Ca 2Cu 3O 10

Abstract

63Cu, 17O and 205Tl NMR have been performed in the high- T c superconductor Tl 2Ba 2Ca 2Cu 3O 10 whose T c(max) is 127 K. The hole densities at Cu and oxygen sites in the CuO 2 plane have been extracted from the nuclear quadrupole frequency ν Q . The striking feature is that the Cu holes are significantly transferred to oxygen site due to strong hybridization between Cu and oxygen. From an analysis of T 1 and T 2 G , it has been found that the spectral weight of the spin fluctuation is transferred to higher energy compared to YBa 2Cu 3O 7, while the magnetic correlation length ξ does not differ much. Thus, it is suggested that the higher T c is due to higher characteristic energy of spin fluctuations, i.e. the superconductivity is spin fluctuation mediated. The superconducting properties are consistently explained by a d-wave superconductivity model with a finite density of states (DOS) at the Fermi level. We show that the disorder of the Ca/TlO layer caused by the partial inter-substitution of Tl and Ca is responsible for the potential scattering to produce such a DOS. It is found that if such a potential scattering were absent, T c would go up to 132 K which is quite close to the record T c realized in the Hg based compound.