Investigations of the core structure of magnetic vortices in type-II superconductors using muon spin rotation

Muon spin rotation (?SR) has emerged as the leading experimental probe of the effective size of magnetic vortices in type-II superconductors. ?SR data on several different classes of type-II superconductors show that the inner structure of a vortex can depend quite strongly on temperature and the strength of the external magnetic field. In this paper it is shown that these behaviours are related to the quasiparticle excitation spectrum both inside and outside of the vortex cores. Here we establish that the vortex core size determined by means of ?SR is particularly sensitive to the nature of the superconducting energy gap(s) and the symmetry of the Fermi surface. A survey of results for different superconductors arrives at the conclusion that the large vortex core size observed in YBa2Cu3O7?? is due to CuO chain superconductivity.