An optical twist for triplet superconductors

The discovery of superconductivity in UPt3 immediately led to ideas and speculations about how the electrons pair up and condense into a superconducting state. Specifically, questions have surrounded the symmetry of the order parameter in these materials (a measure of the density of the condensed electron pairs, and of their phase). From the outset, it was suspected that these so-called heavy-fermion systems were “odd-parity” or “p-wave” superconductors; that is, instead of the electrons pairing up into spin-singlet states with opposite spins as in conventional superconductors, they would form spin-triplet states where the spins of the paired electrons point in the same direction. To date, consensus concerning the microscopic pairing mechanism applicable to these heavy-fermion systems has been lacking. Schemm et al. reported results of magneto-optical experiments that define the nature of the superconducting pairing in these compounds. The Kerr-rotation experiments provide compelling evidence in favor of the odd-parity mechanism, and show that UPt3 belongs to the same universality class as superfluid 3He and the ruthenates