Terahertz studies of superconducting gaps in Co-doped BaFe2As2 pnictide superconductors

Paolo Dore 1 , Boby Joseph 2 , Stefano Lupi 1 , and Andrea Perucchi 3
  • 1 CNR-SPIN and Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2, 00185 Roma, Italy
  • 2 Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2, 00185 Roma, Italy
  • 3 Sincrotrone Trieste, S.C.p.A., Area Science Park, I-34012, Basovizza, Trieste, Italy


In the present paper we report a summary of the infrared studies on the multi-band Ba(Fe1-xCox)2As2 pnictide system, devoted to the detection of superconducting gaps in the terahertz region. Generally, results obtained in the superconducting state indicate the presence of two gaps, but univocal results have not been obtained so far. We show that all the literature gap values of the Ba(Fe1-xCox)2As2 system, when put together as a function of Tc, show a tendency to cluster along two main curves, thus allowing to describe the seemingly contradictory reports into a unified perspective. Below a temperature around 20 K, the sizes of the two gaps as a function of Tc seem to have a BCS-like linear behavior, but with different slopes. In particular, the Δ/kBTc ratio is compatible with the weak-coupling BCS prediction (1.76) for the large gap, while it is close to 1 for the small gap. For Tc above 20 K, a clear supra-linear behavior is observed for the large gap. Although not so clear, such a tendency is also observable for the small gap.

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