Muon spin rotation measurement of the magnetic field penetration depth in Ba(Fe0.926Co0.074)2As2: Evidence for multiple superconducting gaps

We have performed transverse field muon spin rotation measurements of single crystals of Ba(Fe0.926Co0.074)2As2 with the applied magnetic field along the ĉ direction. Fourier transforms of the measured spectra reveal an anisotropic line-shape characteristic of an Abrikosov vortex lattice. We have fit the μSR spectra to a microscopic model in terms of the penetration depth λ and the Ginzburg-Landau parameter κ. We find that as a function of …