Temperature dependence of the penetration depth in pnictides measured locally with scanning SQUIDs

Using a Scanning SQUID Microscope, we locally measure changes in the ab-plane penetration depth $\Delta\lambda_{ab}(T)$ of superconducting samples. Local measurements allow us to check for electronic homogeneity, including $T_c$ homogeneity, as well as to minimize the possibility of sample-geometry-dependent errors, including contributions from the c-axis penetration depth. We report results on lead as well as on pnictide superconductors, including $Ba(Fe_{0.95}Co_{0.05})_{2}As_{2}$ and LaFePO. In LaFePO, we find a linear-T dependence with a slope of 143$\pm$15 {\AA}/K, suggesting well-developed line nodes in the superconducting order parameter.