Mysteries in the superconductivity of Sr2RuO4

Sr2RuO4 is an unconventional oxide superconductor with Tc = 1.5 K. Although a majority of experimental results are consistent with a $d_{x^2-y^2}$ order parameter, there are a set of results that point to something unusual about the superconductivity, including a possibility that the order parameter breaks time reversal symmetry. The mechanism that drives the superconductivity is not known and might be something new. In this talk, I will give an introduction to the superconductivity of Sr2RuO4, and will then go into depth on two sets of results. One is the use of uniaxial stress to probe whether the superconducting order parameter has two components. The other is muon spin rotation, which has traditionally been used to probe whether superconducting order parameters break time reversal symmetry, but for which data on Sr2RuO4 indicate that a fundamental re-think may be required.