  We report muon spin rotation measurements on a single crystal of the marginal
type-II superconductor V. The measured internal magnetic field distributions
are modeled assuming solutions of the Ginzburg-Landau (GL) equations for an
ideal vortex lattice obtained using (i) an iterative procedure developed by
E.H. Brandt, Phys. Rev. Lett. 78, 2208 (1997) and (ii) a variational method.
Both models yield qualitatively similar results. The magnetic penetration depth
(lambda) and the GL coherence length (xi) determined from the data analysis
exhibit strong field dependences, which are attributed to changes in the
electronic structure of the vortex lattice. The zero-field extrapolated values
of lambda and the GL parameter kappa agree well with values obtained by other
experimental techniques that probe the Meissner state.

Superconductivity