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The optical conductivity of the superconducting state in BaFe2As2 based superconductors

In iron-arsenide superconductors up to five bands cross the Fermi level. A
growing body of evidence points towards an all electronic pairing mechanism in
which interband coupling plays a fundamental role. This interaction lead to a
proposed s+/- superconducting gap symmetry, where gaps from different bands
have a phase shift of pi. BaFe2As2 is a key material in understanding the
superconducting properties of pnictides. Doping of Ba sites with K, replacement
of Fe by Co or substitution of As by P, all lead to superconductors with
reasonably high critical temperatures, yet with different superconducting
characteristics. In this talk I will present the optical conductivity of these
superconducting families and show the effect of different dopings in the gap
structure. I will discuss the data in the framework of the s+- symmetry, impurity
induced pair breaking and nodes in the gap.