Superconducting order parameter of Sr2_2RuO4_4: a microscopic perspective

The character of the superconducting phase of Sr$_2$RuO$_4$, is topic of a longstanding discussion. The classification of the symmetry allowed order parameters has relied on the tetragonal symmetry of the lattice and on cylindrical Fermi surfaces, usually taken to be featureless, not including the non-trivial symmetry aspects related to their orbital content. Here we show how the careful account of the orbital degree of freedom in Sr$_2$RuO$_4$, leads to a much richer classification of order parameters. We analyse the stability and degeneracy of these new order parameters from the perspective of the concept of superconducting fitness and propose a new best order parameter candidate.Comment: 13 page

The penetration depth in Sr2RuO4: Evidence for orbital dependent superconductivity

The apparent $T^2$-temperature dependence of the London penetration depth in Sr$_2$RuO$_4$ is discussed on the basis of a multi-gap model with horizontal line nodes. The influence of the nodes in combination with nonlocal electromagnetic response leads to low-temperature behaviors as $-T^2\ln T$ in the London limit and as $T^2$ in the Pippard limit. These behaviors appear only at very low temperature. On the other hand, the interplay of the superconductivity of different bands is responsible for the observed $T^2$-like behavior over the wide temperature range. The experimental data can be fitted well with a set of material parameters as was used in the specific heat fitting.Comment: 7 pages, 3 figures in EPL styl