The thermal conductivity κ 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 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-xKxFe2As2 is reconstructed by the antiferromagnetic order.
J. P. Reid and M. A. Tanatar and X. G. Luo and H. Shakeripour and S. R. De Cotret and A. Juneau-Fecteau and J. Chang and B. Shen and H. H. Wen and H. Kim and For full list of authors, see publisher's website., "Doping Evolution of the Superconducting Gap Structure in the Underdoped Iron Arsenide Ba₁₋ₓKₓFe₂As₂ Revealed by Thermal Conductivity," Physical Review B, vol. 93, no. 21, article no. 214519, American Physical Society (APS), Jun 2016.
The definitive version is available at https://doi.org/10.1103/PhysRevB.93.214519
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30 Jun 2016