Doping evolution of the superconducting gap structure in the underdoped iron arsenide Ba1−xKxFe2As2 revealed by thermal conductivity --- Physical Review B 93, 214519 (2016) / arXiv:1602.03914

Doping evolution of the superconducting gap structure in the underdoped iron arsenide Ba1−xKxFe2As2 revealed by thermal conductivity 

J.-Ph. Reid,¹ M. A. Tanatar,² X. G. Luo,¹ H. Shakeripour,^1,3 S. Rene de Cotret,¹ A. Juneau-Fecteau,¹ J. Chang,¹ B. Shen,⁴ H.-H. Wen,^4,5 H. Kim,² R. Prozorov,² N. Doiron-Leyraud,¹ and Louis Taillefer^1,5,*

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

2.Ames Laboratory USDOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA

3.Department of Physics, Isfahan University of Technology, Isfahan 84156-83111, Iran

4.Center for Superconducting Physics and Materials, National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China

5.Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8

(Received 27 January 2016; revised manuscript received 9 May 2016; published 30 June 2016)

Physical Review B 93, 214519 (2016) / arXiv:1602.03914

Abstract

The thermal conductivity κ of the iron-arsenide superconductor Ba1−x Kx Fe2 As2 was measured for heat currents parallel and perpendicular to the tetragonal c axis at temperatures down to 50 mK and in magnetic fields up to 15 T. Measurements were performed on samples with compositions ranging from optimal doping (x = 0.34, Tc = 39 K) down to dopings deep into the region where antiferromagnetic order coexists with superconductivity (x = 0.16, Tc = 7 K). In zero field, there is no residual linear term in κ(T ) as T → 0 at any doping, whether for in-plane or interplane transport. This shows that there are no nodes in the superconducting gap. However, as x decreases into the range of coexistence with antiferromagnetism, the residual linear term grows more and more rapidly with applied magnetic field. This shows that the superconducting energy gap develops minima at certain locations on the Fermi surface and these minima deepen with decreasing x. We propose that the minima in the gap structure arise when the Fermi surface of Ba1−x Kx Fe2 As2 is reconstructed by the antiferromagnetic order.