Probing the enhanced superconductivity and chiral edge current in spin-triplet superconductor strontium ruthenate

This dissertation aims at providing insight into the mechanism of spin-triplet superconductivity in Sr2RuO4, the only Cu-free layered perovskite material found to be superconducting.;The work starts by looking at the Sr2RuO4-Ru eutectic phase featuring Ru islands embedded in a bulk crystal of Sr2RuO 4. The Sr2RuO4-Ru interface was found to be atomically smooth. Surprisingly, even such a clean interface appears not to allow the proximity effect of spin-triplet superconducting gap to enter the Ru islands. The previously observed 3 K-phase superconductivity in this eutectic phase seems to occur away from the interface where dislocations are present.;To pinpoint the enhanced superconductivity to dislocations, micrometer sized flakes of Sr2RuO4 were studied, in which the effect of dislocations on Tc can be studied without the influence of Ru islands. The origin of the 3 K-phase was shown to be the presence of dislocations, near which the crystalline symmetry is lowered. The reduced symmetry leads naturally to an enhanced Tc, as revealed by a phenomenologically theory.;After that, a different experiment is presented. Unconventional Josephson coupling was shown to occur in ramp-type junctions on Sr2RuO 4 flakes. The chiral edge current was measured using Josephson interferometry. An upper limit of the edge current was obtained to be as small as 0.1 percent of the theoretically predicted value. Such an upper limit was found to be similar to the measured transport critical current density of the Sr 2RuO4 flakes.;The results suggest that the interlayer coupling and the multiband nature of the electronic structure are important to the mechanism of superconductivity.