Hydrostatic pressure dependence of the superconducting transition temperature of HgBa(sub 2)CaCu(sub 2)O(sub 6+(delta)) and HgBa(sub 2)Ca(sub 2)Cu(sub 3)O(sub 8+(delta))

摘要

The dependence of the superconducting transition temperature (Tc)(P) on purely hydrostatic pressure to 0.9 GPa has been determined in ac susceptibility studies in a He-gas pressure system for optimally doped ceramic samples of HgBa(sub 2)CaCu(sub 2)O(sub 6+(delta)) and HgBa(sub 2)Ca(sub 2)Cu(sub 3)O(sub 8+(delta)) with superconducting transitions at (Tc)(0) (approx equal) 126.6 K and 133.9 K, respectively. (Tc) increases reversibly under hydrostatic pressure at the rates, d(Tc)/dP (approx equal) +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 HgBa(sub 2)CuO(sub 4+(delta)), where d(Tc)/dP (approx equal) +1.72 (+-) 0.05 K/GPa. Remarkably, the logarithmic volume derivative of (Tc) is nearly identical for all three compounds, dln(Tc)/dlnV (approx equal) (minus)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.