Half quantum vortices and Majorana fermions in triplet superconductors
Half quantum vortices (HQVs) in superfluid 3 He A have been speculated since 1976. Two years ago, Yamashita et al(1) reported a very unusual NMR satellite in the rotating superfluid 3 He A in a parallel plate geometry. Recently this satellite has been interpreted in terms of HQVs(2). Also, the strong flux pinnings in the triplet superconductors UP t3, Sr2RuO4 and U1−xT hxBe13 have been discovered by Mota and her colleagues(3)(4) which are interpreted in terms of HQVs(5)(6)(7). We shall first review the bound state spectra around a single vortex in unconventional superconductors, which provides the necessary background. In particular, we find the zero modes of the Majorana fermions in some of triplet superconductors UP t3, Sr2RuO4 and CeP t3Sn. Armed with these results we analyze the microscopic aspects of HQVs in UP t3 and Sr2RuO4. We compute the quasiparticle density of states and the local magnetic field around HQVs, which should be accessible to scanning tunneling microscopy (STM), micromagnetometry and neutron scattering below 300 mK.