Superconductivity

The Superconductivity Group is centred around Doug Bonn, Walter Hardy and Ruixing Liang and their long-standing interest in high temperature superconductors and other strongly correlated electron systems. At the heart of this research is the synthesis of high purity single crystals, primarily using flux-growth techniques. These include very high purity crystals of YBa₂Cu₃O_6+x with carefully tailored oxygen doping, the overdoped cuprate Tl₂Ba₂CuO_6+x and a number of the new pnictide-based superconductors such as LiFeAs. This materials effort fuels multiple research projects, providing tight feedback between the optimization of materials preparation and the experiments being performed on them.

In addition to an array of standard characterization tools, we also extensively employ microwave measurement techniques which are used to probe the behavior of both the superfluid in these materials and the quasiparticle excitations out of the groundstate. High-Q superconducting microwave cavities are used to measure the complex microwave surface impedance at fixed frequencies and we have also developed a broadband microwave spectrometer covering the 0-25 GHz range that is unique in the world.

Recent interest has also turned towards Scanning Tunneling Microscopy and Spectroscopy, in collaboration with Sarah Burke and Yan Pennec. These techniques are used to perform spectroscopic measurements of the superconducting gap, quasiparticle interference as a probe of the gap and bandstructure, and the effects of impurities. Future work is aimed at in situ deposition to manipulate the surfaces being probed, for instance tuning the doping on a polar surfaces of YBa₂Cu₃O_6+x and growth of novel heterostructures.