Anisotropy and two-gap contributions to flux lattice in MgB2 superconductor and Mg1-xAlxB2 alloys

We present transverse field mu SR measurements of the flux lattice field distribution in dense pellets of MgB2 and of the alloy Mg1-xAlxB2. In the present work we focus on the analysis of the data, comparing the second moment of the calculated and experimental field distributions. Starting from the standard model, we modified the calculation to include the presence of two length scales, the diffusion lengths of the sigma and pi pairs. We further introduce a partially anisotropic single gap model, adapted to the electronic structure of MgB2, and a partially anisotropic two-band model. We confirm that the two distinct gaps can better describe the field dependence of the data. (c) 2005 Published by Elsevier B.V.