PRESSURE-DEPENDENCE OF THE SUPERCONDUCTING CRITICAL-TEMPERATURE T-C OF HGBA2CA2CU3O8+X UP TO 26-GPA

The pressure dependence of the newly discovered mercury-compound HgBa2Ca2Cu3O8+x (Hg-1223) has been studied in detail up to 26 GPa in a cryogenic diamond anvil cell on a sample with a single superconducting phase. Although initially T-c increases from 135 K at a rate of 1.0 K/GPa, at intermediate pressures partial derivative T-c/partial derivative p decreases rapidly. When pressure is increased further, however, T-c rises again significantly up to 145 K at 26 GPa (where partial derivative T-c/partial derivative p similar or equal to 0.4 K/GPa). These results can be understood qualitatively on the basis of a charge-transfer model which allows a non-homogeneous distribution of holes among the inequivalent CuO2 layers.