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

摘要

The recent discovery of superconductivity below a transition temperature (T_c) of 94 K in HgBa_2CuO_(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 CuO_2 layer per unit cell. Here we provide support for this conjecture, with the discovery of superconductivity above 130 K in a material containing HgBa_2Ca_2Cu_3O_(1+x) (with three CuO_2 layers per unit cell), HgBa_2CaCu_2O_(6+x) (with two CuO_2 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 Tl_2Ba_2Ca_2Cu_3O_(10) (refs 2,3).