Impurity Effects on the Energy Gap in Fe-doped Bi2212

We performed scanning tunnelling microscopy/spectroscopy (STM/STS) on Fe-doped Bi2212. The Fe substitution for Cu causes a strong spatial inhomogeneity in STS spectra. The energy gap (Δ1 ∼80mV) has a sub-gap (Δ2 ∼70mV) in some distinct locations on the sample surface. We find that the gap edge peaks are largely depressed and only the sub-gap survives across the region where the spatial modulation of the local density of states is stronger. This indicates, that Δ1 anti-correlates with Δ2.