Vortex imaging in unconventional superconductors

The real space imaging of vortices in unconventional superconductors not only provides important information about the effectiveness of flux pinning that can inform high current applications, but also yields crucial insights into the form of the superconducting order parameter. For example, the structure of the vortex lattice reflects effective mass and order parameter anisotropies within the material, and profiles of isolated vortices provide a local measure of the magnetic penetration depth that can be used to infer the superfluid density. We describe here the analysis of recent studies whereby state-of-the-art scanning Hall probe microscopy (SHPM) has been used to perform vortex-resolved magnetic imaging on two distinct families of unconventional superconductors. Two sets of results will be analysed in detail; (i) vortex lattice structural transitions in the p-wave superconductor Sr 2RuO 4 that reflect underlying anisotropies in the system and (ii) a quantitative analysis of vortex profiles in Co-doped 122 pnictide superconductors (SrFe 2- x Co x As 2 & BaFe 2- x Co x As 2) that allows one to infer the temperature-dependent superfluid density. The latter has then been compared with predictions for different order parameter models for a multiband superconductor.