  We report muon spin rotation measurements on the conventional type-II
superconductor V3Si that provide clear evidence for changes to the inner
structure of a vortex due to the delocalization of bound quasiparticle core
states. The experimental findings described here confirm a key prediction of
recent microscopic theories describing interacting vortices. The effects of
vortex-vortex interactions on the magnetic and electronic structure of the
vortex state are of crucial importance to the interpretation of experiments on
both conventional and exotic superconductors in an applied magnetic field.
