# Doping dependence of heat transport in the iron-arsenide superconductor BaFe$ {1-x}$Co$ x$$ 2$As$ 2$: from isotropic to strongly $k$-dependent gap structure - Condensed Matter > Superconductivity

Doping dependence of heat transport in the iron-arsenide superconductor BaFe$ {1-x}$Co$ x$$ 2$As$ 2$: from isotropic to strongly $k$-dependent gap structure - Condensed Matter > Superconductivity - Download this document for free, or read online. Document in PDF available to download.

Abstract: The temperature and magnetic field dependence of the in-plane thermalconductivity $\kappa$ of the iron-arsenide superconductorBaFe$ {1-x}$Co$ x$$ 2$As$ 2$ was measured down to $T \simeq 50$ mK and up to$H = 15$ T as a function of Co concentration $x$ in the range 0.048 $ \leq x\leq $ 0.114. In zero magnetic field, a negligible residual linear term in$\kappa-T$ as $T \to 0$ at all $x$ shows that there are no zero-energyquasiparticles and hence the superconducting gap has no nodes in the $ab$-planeanywhere in the phase diagram. However, the field dependence of $\kappa$reveals a systematic evolution of the superconducting gap with doping $x$, fromlarge everywhere on the Fermi surface in the underdoped regime, as evidenced bya flat $\kappa H$ at $T \to 0$, to strongly $k$-dependent in the overdopedregime, where a small magnetic field can induce a large residual linear term,indicative of a deep minimum in the gap magnitude somewhere on the Fermisurface. This shows that the superconducting gap structure has a strongly$k$-dependent amplitude around the Fermi surface only outside theantiferromagnetic-orthorhombic phase.

Author: ** M. A. Tanatar, J. P. Reid, H. Shakeripour, X. G. Luo, N. Doiron-Leyraud, N. Ni, S. L. Bud'ko, P. C. Canfield, R. Prozorov, L**

Source: https://arxiv.org/