The low-field susceptibility of the superconducting state of Sr2RuO4

Sr2RuO4 has long been considered as a textbook example of a system where superconductivity develops from a strongly correlated Fermi liquid. It has generated considerable interest as a test of theory for many reasons including: (i) it has a relatively simple layered structure; (ii) very clean samples can be prepared and, (iii) its magnetic excitations are well-characterised. New NMR Knight shift and polarized neutron scattering (PNS) measurements of the susceptibility in the superconducting state have brought into question the accepted pairing wavefunction. Thus, in the last year numerous candidate superconducting states based on magnetically mediated pairing and ab-initio calculations have been proposed. Here we propose to make further PNS measurements to constrain the allowed superconducting states.