Indirect-exchange coupling and high-TC superconductivity: analysis of TC as a function of pressure in Hg1−xAuxBa2Ca2Cu3Oy. Comparison with other Hg-cuprates

Results of recent experiments by Acha et al. [Phys. Rev. B 57 (1998) R5630] on the effect of pressure on critical temperatures of four samples of the mercury cuprate Hg1−xAuxBa2Ca2Cu3Oy, at different Au doping levels x, are analyzed in the framework of indirect-exchange Cooper pair formation via diamagnetic oxygen anions, developed earlier. It is found that all experimental results are quantitatively explained on this basis, and that partial substitution of Hg by Au must imply a hole doping process in the CuO2 layers. In particular, values of dTC/dP at P=0 are all positive, in the range of doping investigated, in spite of the four systems being hole-overdoped. We also show that pressure dependence of a proximity effect as suggested in the Reference quoted for the undoped cuprate cannot be the cause of the large increase in critical temperature observed with this system.