HYDROSTATIC-PRESSURE ON HGBA2CACU2O6+DELTA AND HGBA2CA2CU3O8+DELTA

The superconducting transition temperature Tc and its pressure dependence dTc/dP of HgBa2CaCu2O 6+δ (Hg-1212) and HgBa2Ca2Cu 3O8+δ (Hg-1223) were measured up to 17 kbar. T c increases with pressure approximately linearly for both compounds before oxidation. However, the nonlinearity in the Tc-P correlation shows up after oxidation in both compounds. For Hg-1212, the average dT c/dP decreases as oxygen doping increases, while it increases in Hg-1223. These observations are in conflict with the modified pressure-induced charge-transfer model, but might be attributed to the possible existence of fine electronic structure. These observations suggest that a Tc much higher than 140 K might be achievable in Hg-1223 by means of higher physical or chemical pressure.