Mapping the superfluid density in an Iron-based Superconductor

Cooper pairs can tunnel through the vacuum barrier between two superconducting electrodes, known as a Josephson junction. Depending on the properties of the junction and the environment, one can extract the superconducting order parameter from the current-voltage spectra. Here, I will present the Josephson tunneling spectroscopic results of an unconventional Fe-based superconductor acquired with a superconducting STM tip. We demonstrate the Josephson tunneling induced characteristic current-voltage curves close to zero bias on a Pb(111) surface and a Fe-based superconductor. I will discuss the spatial variations of the superfluid density in this correlated superconductor and reveal their correlation with an inhomogeneous quasiparticle density of states.