Observation of Momentum-Confined In-Gap Impurity State in Ba0.6K0.4Fe2As2: Evidence for Antiphase s± Pairing

Abstract

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 above the superconducting critical temperature, for which the spectral weight is confined in momentum space near the Fermi wave-vector positions. We demonstrate, supported by theoretical simulations, that this in-gap state originates from weak scattering between bands with opposite sign of the superconducting-gap phase. This weak scattering, likely due to off-plane nonmagnetic (Ba, K) disorder, occurs mostly among neighboring Fermi surfaces, suggesting that the superconducting-gap phase changes sign within holelike (and electronlike) bands. Our results impose severe restrictions on the models promoted to explain high-temperature superconductivity in these materials.

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Zhang, P., Richard, P., Qian, T., et al.. "Observation of Momentum-Confined In-Gap Impurity State in Ba0.6K0.4Fe2As2: Evidence for Antiphase s± Pairing." Physical Review X, 4, no. 3 (2014) American Physical Society: https://doi.org/10.1103/PhysRevX.4.031001.

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