Local measurement of the penetration depth in the pnictide superconductor Ba(Fe0.95Co0.05)2As2

Abstract

We use magnetic force microscopy (MFM) to measure the local penetration depth λ in Ba(Fe0.95Co0.05)2As2 single crystals and use scanning superconducting quantum interference device susceptometry to measure its temperature variation down to 0.4 K. We observe that superfluid density ρs over the full temperature range is well described by a clean two-band fully gapped model. We demonstrate that MFM can measure the important and hard-to-determine absolute value of λ, as well as obtain its temperature dependence and spatial homogeneity. We find ρs to be uniform on the submicron scale despite the highly disordered vortex pinning.