From d-wave to s-wave pairing in the iron-pnictide superconductor (Ba,K)Fe2As2 --- Superconducting Science and Technology 25, 084013 (2012) / arXiv:1207.5719

From d-wave to s-wave pairing in the iron-pnictide superconductor (Ba,K)Fe₂As₂

J-Ph Reid¹, A Juneau-Fecteau¹, R T Gordon¹, S Rene de Cotret¹, N Doiron-Leyraud¹, X G Luo¹, H Shakeripour¹, J Chang¹, M A Tanatar^2,3, H Kim^2,3, R Prozorov^2,3, T Saito⁴, H Fukazawa⁴, Y Kohori⁴, K Kihou⁵, C H Lee⁵, A Iyo⁵, H Eisaki⁵, B Shen⁶, H-H Wen^6,7 and Louis Taillefer^1,7

1. Departement de Physique and RQMP, Universite de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada

2. Ames Laboratory, Ames, IA 50011, USA

3. Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA

4. Chiba University and JST-TRIP, Japan

5. AIST and JST-TRIP, Japan

6. Center for Superconducting Physics and Materials, Department of Physics, Nanjing University, Nanjing 210093, PRC

7. Canadian Institute for Advanced Research, Toronto, ON, M5G 1Z8, Canada 

Superconducting Science and Technology 25, 084013 (2012) / arXiv:1207.5719

Abstract

The nature of the pairing state in iron-based superconductors is the subject of much debate. Here we argue that in one material, the stoichiometric iron pnictide KFe2As2, there is overwhelming evidence for a d-wave pairing state, characterized by symmetry-imposed vertical line nodes in the superconducting gap. This evidence is reviewed, with a focus on thermal conductivity and the strong impact of impurity scattering on the critical temperature Tc. We then compare KFe2As2 to Ba0.6K0.4Fe2As2, obtained by Ba substitution, where the pairing symmetry is s-wave and the Tc is ten times higher. The transition from d-wave to s-wave within the same crystal structure provides a rare opportunity to investigate the connection between band structure and the pairing mechanism. We also compare KFe2As2 with the nodal iron-based superconductor LaFePO, for which the pairing symmetry is probably not d-wave, but more likely s-wave with accidental line nodes.

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