Transport properties of TlBa2Ca2Cu3Oy in an over-doped state

It has recently been found that the Tc of TlBa2Ca2Cu3Oy (Tl-1223) is equivalent to that of Hg-1223, known as the highest Tc superconductor at present. Measurements of resistivity, Hall effect, and thermoelectric power were carried out on Tl-1223 having various doping levels from high over-doping to slight over-doping. As-synthesized materials were prepared under high pressure and deoxidized by post-annealing under various conditions. The results were compared with the data for under-doped Hg-1223 reported by Fukuoka et al. The carrier concentration estimated from the thermoelectric power in both over-doped Tl-1223 and under-doped Hg-1223 showed a simple bell-shaped Tc behavior. It was also observed that the Hall effect behavior of over-doped Tl-1223 resembles that of over-doped Hg-1223. These results strongly suggest that the highest Tc values for the Tl and Hg systems are nearly identical at the same carrier concentration per CuO2 plane.