| Sr2RuO4, an unconventional superconducting material with Tc = 1.5 K, was predicted to possess a superconducting state with an order parameter of odd-parity symmetry. Numerous experiments have given support to the prediction, but none of these experiments has been sufficiently definitive to allow certainty about the symmetry of the order parameter. Direct evidence of odd-parity symmetry can be obtained from a phase-sensitive experiment which measures interference in the critical current between two coupled Josephson junctions.; Odd-parity symmetry in Sr2RuO4 is established here by a phase-sensitive measurement using Josephson junctions on single crystals of Sr2RuO4, with the junctions prepared on opposite sides of the crystal. Measurements of the critical current versus external magnetic flux for these samples show quantum interference between the junctions, with the critical current at a minimum when zero external flux is applied. For junctions on opposite sides, this result is possible only for a material with odd-parity symmetry.; The phase-sensitive measurements are difficult because of a suppression of superconductivity at the surface of Sr2RuO4 crystal which is demonstrated by single-particle tunneling measurements. Tunneling spectra for Au-Sr2RuO4 junctions show no features due to super conductivity in Sr2RuO4. However, metal alloys such as Hg-In and Au-In which wet the Sr2RuO4 surface are shown to form Josephson junctions with finite supercurrent despite the normal surface layer, making possible the phase-sensitive experiment.; In addition, previous analysis of experiments on Sr2RuO 4 has assumed weak spin-orbit coupling in the material. A large product of critical current and normal state resistance (IcR n) for Au-In-Sr2RuO4 junctions has been measured and is shown to be an indication of strong spin-orbit coupling near the Sr2RuO4 surface.; The full text is always available for free at http://etda.libraries.psu.edu/. |
