Superconductivity up to 164 K in HgBa₂Ca_m-1Cu_mO_2m+2+δ (m=1, 2, and 3) under quasihydrostatic pressures

The superconducting transition temperatures (T_c’s) of optimally doped HgBa₂Ca_m-1Cu_mO_2m+2+δ (Hg 1:2:m-1:m) with m=1, 2, and 3 and Hg_1-xPb_xBa₂Ca₂Cu₃O_8+δ [Hg(xPb) 1:2:2:3] have been investigated resistively under quasihydrostatic pressures up to 45 GPa. There seems to be a universal upward shift of T_c under pressure, regardless of m, for all Hg 1:2:m-1:m, implying a common origin for all compounds. Record high T_c’s of 164, 154, and 118 K were reached for the optimally doped Hg 1:2:m-1:m with m=3, 2, and 1, respectively. However, the T_c enhancement is suppressed by Pb substitution, suggesting the possibility that Hg plays an important role in these compounds.