Hydrostatic pressure on HgBa2CaCu2O6+δ and HgBa2Ca2Cu3O8+δ

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Abstract
The superconducting transition temperature Tc and its pressure dependence dTc/dP of HgBa2CaCu2O6+δ (Hg‐1212) and HgBa2Ca2Cu3O8+δ (Hg‐1223) were measured up to 17 kbar. Tc 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 dTc/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.