Pairing symmetry of the bulk and eutectic phases of Sr₂RuO₄ probed by single-particle and Josephson tunneling measurements

In addition to the ultrapure bulk phase, the growth of single crystals of Sr₂RuO₄ by the floating zone technique will result in a eutectic phase featuring islands of single crystal Ru embedded in the bulk Sr₂RuO₄. The size of the Ru island varies - ranging from a submicron to tens of microns – and the interface between Ru and Sr₂RuO₄ is atomically sharp. The interface region on the Sr₂RuO₄ side features an enhanced superconducting transition temperature (T_c) of roughly 3 K, which is larger than those of Ru and Sr₂RuO₄. Single-particle and Josephson tunneling measurements on the bulk and 3-K phases were carried out using junctions prepared by pressing thin indium wire onto the cleaved ab surface of single Sr₂RuO₄ crystals containing sparsely distributed Ru islands. Analysis of features in the tunneling spectrum and evidence of a possible mixed pairing state within the Ru island stabilized by the Joesphson effect will be presented.