NMR study on high-TC cuprate TlBa2(Y1−xCax)Cu2O7 with the wide range of hole concentration from antiferromagnetic to overdoped region Original Research Article

Tl-NMR spectra and the spin–lattice relaxation rate have been measured for Tl-based high-TC cuprate TlBa2(Y1−xCax)Cu2O7 with a wide region of the hole concentration from antiferromagnetic (x=0) to slightly overdoped (x=1). On doping, the superconducting transition temperature TC is raised abruptly from 0 to 100 K at x=0.6. In the entire superconducting region of x=0.6–1.0, the Knight shift is temperature independent of the normal state, showing no traces of the spin-gap. The spin–lattice relaxation rate shows a spin-gap around 150 K, which is much higher than TC. These two facts in striking contrast indicate that the lightly doped region does not exist or is confined within an extremely narrow region of Ca-concentration.