The Unconventional Superconductivity of Sr₂RuO₄

We review the evidence for unconventional superconductivity in Sr2RuO4; the pairing in this material is certainly non-s-wave, and most of the current observations can be accounted for by a particular p-wave state, which is doubly degenerate and breaks time-reversal symmetry. Our observations of the flux lattice by small-angle neutron scattering contribute to this picture. The square flux: lattice and the intensity of the diffracted signal indicate that superconductivity resides primarily on the gamma sheet of the Fermi surface, which is derived from the Ru - d(xy) orbitals. This is in agreement with the "orbital-dependent" p-wave scenario. Furthermore, the shape of the flux lines derived from these measurements is strongly indicative of a two-component order parameter.