H. H. Wen

Pressure-induced Fermi-surface reconstruction in the iron-arsenide superconductor Ba 1 − x K x Fe 2 As 2 : Evidence of a phase transition inside the antiferromagnetic phase

E. Hassinger, ∗ G. Gredat, F. Valade, S. René de Cotret, A. Juneau-Fecteau, J.-Ph. Reid, H. Kim, M. A. Tanatar, R. Prozorov, B. Shen, H.-H. Wen, 5 N. Doiron-Leyraud, and Louis Taillefer 5, † Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1 Ames Laboratory, Ames, Iowa 50011, USA Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA Center for Superconducting Physics and Materials, National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8 (Dated: May 1, 2014)

Doping evolution of the superconducting gap structure in the underdoped iron arsenide Ba 1 − x K x Fe 2 As 2 revealed by thermal conductivity

The thermal conductivity kappa of the iron-arsenide superconductor Ba1-xKxFe2As2 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 kappa(T) as T goes to 0 at any doping, whether for in-plane or inter-plane 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-xKxFe2As2 is reconstructed by the antiferromagnetic order.