Gap structure of iron-based superconductors via directional thermal conductivity

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Date/Time:Thursday, 17 Nov 2011 - Saturday, 19 Nov 2011
Location:ROOM 18/19 PHYSICS
Channel:Condensed Matter Physics
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Jean-Philippe Reid

Departement de physique & RQMP, Universite de Sherbrooke, Sherbrooke, Quebec, Canada J1K 2R1

Because the structure of the superconducting gap as a function of direction reflects the pairing
interaction, it can shed light on the nature of the pairing mechanism. In the iron pnictides, the
experimental situation in this respect remains unclear and so far suggests the lack of a universal
picture. Here I present a systematic study of the superconducting gap structure through directional
thermal conductivity measurements [1] on hole-doped K-Ba122 [2,3], electron-doped Co-Ba122
[4,5], self-doped LiFeAs [6] and the chalcogenide FeTeSe.
We observe a general trend for the evolution of the superconducting gap with doping. At optimal
doping, the gap structure is nodeless and isotropic (3D). Away from optimal doping, nodes appear
on the Fermi surface at the edges of the superconducting dome, as seen for K-Ba122 and Co-Ba122.
This strongly suggests that the presence of these nodes is accidental and therefore not imposed by
symmetry. It would instead depend on the competition between intra- and inter-band interactions
controlled by the evolving band structure and Fermi surface, and by the onset of antiferromagnetic
Work done in collaboration with M. A. Tanatar, X. G. Luo, H. Shakeripour, R. Gordon,
A. Juneau-Fecteau, N. Doiron-Leyraud, S. René de Cotret, F. Laliberté, E. Hassinger, J. Chang, N.
Ni, S. L. Bud'ko, P. C. Canfield, H. Kim, R. Prozorov, B. Shen, H. Luo, Z. Wang, H.-H. Wen,
K. Cho, Y. J. Song, Y. S. Kwon, and Louis Taillefer.
[1] H. Shakeripour et al., New Journal of Physics 11, 055065 (2009).
[2] X. G. Luo et al., Physical Review B 80, 140503 (2009).
[3] J.-Ph. Reid et al., arXiv:1105:2232.
[4] M. A. Tanatar et al., Physical Review Letters 104, 067002 (2010).
[5] J.-Ph. Reid et al., Physical Review B 82, 064501 (2010).
[6] M. A. Tanatar et al., Physical Review B 84, 054507 (2011).