HYDROSTATIC-PRESSURE DEPENDENCE OF THE SUPERCONDUCTING TRANSITION-TEMPERATURE OF HGBA2CACU2O6+DELTA AND HGBA2CA2CU3O8+DELTA

The dependence of the superconducting transition temperature T(c)(P) on purely hydrostatic pressure to 0.9 GPa has been determined in AC-susceptibility studies in a He-ps pressure system for optimally doped ceramic samples of HgBa2CaCu2O6+delta and HgBa2Ca2Cu3O8+delta with superconducting transitions at T(c)(0) congruent-to 126.6 K and 133.9 K respectively. T(c) increases reversibly under hydrostatic pressure at the rates, dT(c)/dP congruent-to + 1.80 +/- 0.06 K/GPa and + 1.71 +/- 0.05 K/GPa, respectively. Within experimental error, these values are the same as found previously for optimally doped single-layered HgBa2CuO4+delta, where dT(c)/dP congruent-to + 1.72 +/- 0.05 K/GPa. Remarkably, the logarithmic volume derivative of T(c) is nearly identical for all three compounds, dln T(c)/dln V congruent-to -1.20 +/- 0.05, even though the bulk modulus differs by more than 30%. This provides strong evidence that a common mechanism is responsible for the pressure dependence of the superconducting state in all three compounds.