Superconductivity-induced optical anomaly in an iron arsenide

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Abstract

One of the central tenets of conventional theories of superconductivity, including most models proposed for the recently discovered iron-pnictide superconductors, is the notion that only electronic excitations with energies comparable to the superconducting energy gap are affected by the transition. Here, we report the results of a comprehensive spectroscopic ellipsometry study of a high-quality crystal of superconducting Ba0.68 K0.32 Fe2 As2 that challenges this notion. We observe a superconductivity-induced suppression of an absorption band at an energy of 2.5 eV, two orders of magnitude above the superconducting gap energy 2δ≈20 meV. On the basis of density functional calculations, this band can be assigned to transitions from As-p to Fe-d orbitals crossing the Fermi level. We identify a related effect at the spin-density wave transition in parent compounds of the 122 family. This suggests that As-p states deep below the Fermi level contribute to the formation of the superconducting and spin-density wave states in the iron arsenides. © 2011 Macmillan Publishers Limited. All rights reserved.

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Charnukha, A., Popovich, P., Matiks, Y., Sun, D. L., Lin, C. T., Yaresko, A. N., … Boris, A. V. (2011). Superconductivity-induced optical anomaly in an iron arsenide. Nature Communications, 2(1). https://doi.org/10.1038/ncomms1223

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