Appearance of a Maximum ofTcand a Large Negative dTc/dPin the Superconducting Tl-Ba-Ca-Cu-O Compounds under Pressure

Abstract
The pressure dependence of T c for the superconducting Tl-Ba-Ca-Cu-O compounds has been measured. It is found that the pressure coefficients of T c in Tl 2 Ba 2 CaCu 2 O 8 change the sign from positive to negative with a maximum T c and that the highly hole-doped Tl 2 Ba 2 CuO 6 compounds show a large negative value of d T c /d P . These results revealed a new feature of the pressure dependence of T c in the hole-doped superconductors and can be interpreted speculatively in terms of the hole concentration in the CuO 2 planes assuming that the carrier concentration is redistributed with pressure.