Muon spin rotation measurements of the vortex state in vanadium: A comparative analysis using iterative and analytical solutions of the Ginzburg-Landau equations

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 (i) solutions of the Ginzburg-Landau (GL) equations for an ideal vortex lattice obtained using an iterative procedure developed by Brandt [Phys. Rev. Lett. 78, 2208 (1997)], (ii) a variational GL method, and (iii) a modified London model. Remarkably the models yield qualitatively similar results. The magnetic penetration depth lambda and the 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. We find that the zero-field extrapolated value of lambda is essentially independent of the assumed model and agrees well with the value obtained by experimental techniques that probe the Meissner state. On the other hand, only fits to either of the GL models yield reliable values of xi.