Superconductivity above 130 K in the Hg-Ba-Ca-Cu-O system

THE recent discovery¹ of superconductivity below a transition temperature (T_c) of 94 K in HgBa₂CuO_4+δ has extended the repertoire of high-T_c superconductors containing copper oxide planes embedded in suitably structured (layered) materials. Previous experience with similar compounds containing bismuth and thallium instead of mercury suggested that even higher transition temperatures might be achieved in mercury-based compounds with more than one CuO₂ layer per unit cell. Here we provide support for this conjecture, with the discovery of superconductivity above 130 K in a material containing HgBa₂Ca₂Cu₃O_1+x (with three CuO₂ layers per unit cell), HgBa₂CaCu₂O_6+x (with two CuO₂ layers) and an ordered superstructure comprising a defined sequence of the unit cells of these phases. Both magnetic and resistivity measurements confirm a maximum transition temperature of ~ 133 K, distinctly higher than the previous established record value of 125-127 K observed in Tl₂Ba₂Ca₂Cu₃O₁₀ (refs 2,3).