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

Abstract

THE recent discovery^1,2 of a family of mercury-based copper oxide superconductors having transition temperatures^1–3 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, J_c, 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 temperature^1–3 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 ${\text{HgBa}}_{\text{2}}{\text{CaCu}}_{\text{6}}{\text{O}}_{\text{6}+\text{δ}}$ (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 J_c≳10⁷ A cm⁻² at 5 K and J_c∼ 10⁵ A cm⁻² at 110 K, at least an order of magnitude larger than for Bi- or Tl-based films^6–11. 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.