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

Abstract

THE recent discovery1 of superconductivity below a transition temperature (Tc) of 94 K in HgBa2CuO4+δ has extended the repertoire of high-Tc 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 HgBa2Ca2Cu3O1+x (with three CuO2 layers per unit cell), HgBa2CaCu2O6+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). The discovery in 1986 of the first copper oxide superconductor stimulated an explosion of research activity that continues to the present day. The early years of high-temperature superconductivity were characterized by the rapid discovery of many new materials with increasingly high transition temperatures. The record now stands at ~133 K, attributed to a mercury-containing compound reported by Schilling et al. in 1993, although the dream of achieving room-temperature superconductivity has yet to be fulfilled.