Temperature Dependence of the Magnetic Field at a Vortex Center in Type-II Superconducting Vanadium By NMR

The field at a vortex center, $h_v$, was measured in a vanadium foil sample and extrapolated to zero temperature and zero flux density. For an isolated vortex at $T=0\mathrm{}$, $h=1780\mathrm{}\pm 240$ G. At all flux densities it appears that $\frac{\partial h_v}{\partial T}$ is nonzero, even as $T\to 0$.