Observation of momentum-confined in-gap impurity state in Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$: evidence for anti-phase $s_{\pm }$ pairing

P. Zhang, P. Richard, T. Qian +12

We report the observation by angle-resolved photoemission spectroscopy of an impurity state located inside the superconducting gap of Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ and vanishing…