High current densities above 100 K in the high-temperature superconductor HgBa₂CaCu₂O_6+δ;

Abstract

THE recent discovery1, 2 of a family of mercury-based copper oxide superconductors having transition temperatures1–3 above 130 K is of considerable technological interest. But the viability of high-temperature superconductors for many applications will ultimately depend on the size of the current density, Jc, that they are able to support, not only at high temperatures, but also in high magnetic fields. For the cuprate superconductors, and in particular for Hg-based materials, the combination of high transition temperature1–3 and large mass anisotropy implies that the transport properties will be intrinsically limited by large thermal fluctuations and short superconducting coherence lengths4. Here we report that high-quality c-axis-oriented epitaxial films of the compound HgBa2CaCu6O6+δ (Hg-1212; ref. 5) can support large in-plane current densities at temperatures higher than has been achieved for other superconductors. In low magnetic fields oriented normal to the film surface, we find Jc≥107 A cm−2 at 5 K and Jc105 A cm−2 at 110 K, at least an order of magnitude larger than for Bi- or Tl-based films6–11. For in-plane magnetic fields, the critical current (108 A cm−2) is close to the theoretical limit even at high fields, indicative of strong intrinsic pinning in this compound. © 2015 Nature Publisher Group.