Effect of the vortex core on the magnetic field in hard superconductors

Using approximate analytical and numerical solutions of the conventional Ginzburg-Landau equations we calculate the small-angle neutron-scattering cross section and the variance of the field distribution as measured by muon-spin rotation for superconductors with large Ginzburg-Landau parameter κ. Our results prove that a proper account of the finite size of the vortex core is important, even at relatively low fields. This finding provides a natural explanation for the recently observed field dependence of the ${\mathrm{CeRu}}_2$ form factor and of the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.95}$ penetration depth.