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Nodes in the gap structure of the iron arsenide superconductor Ba(Fe1xCox)2As2 from c-axis heat transport measurements

J.-Ph. Reid, M. A. Tanatar, X. G. Luo, H. Shakeripour, N. Doiron-Leyraud, N. Ni, S. L. Bud’ko, P. C. Canfield, R. Prozorov, and Louis Taillefer
Phys. Rev. B 82, 064501 – Published 2 August 2010
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Abstract

The thermal conductivity κ of the iron-arsenide superconductor Ba(Fe1xCox)2As2 was measured down to 50 mK for a heat current parallel (κc) and perpendicular (κa) to the tetragonal c axis for seven Co concentrations from underdoped to overdoped regions of the phase diagram (0.038x0.127). A residual linear term κc0/T is observed in the T0 limit when the current is along the c axis, revealing the presence of nodes in the gap. Because the nodes appear as x moves away from the concentration of maximal Tc, they must be accidental, not imposed by symmetry, and are therefore compatible with an s± state, for example. The fact that the in-plane residual linear term κa0/T is negligible at all x implies that the nodes are located in regions of the Fermi surface that contribute strongly to c-axis conduction and very little to in-plane conduction. Application of a moderate magnetic field (e.g., Hc2/4) excites quasiparticles that conduct heat along the a axis just as well as the nodal quasiparticles conduct along the c axis. This shows that the gap must be very small (but nonzero) in regions of the Fermi surface which contribute significantly to in-plane conduction. These findings can be understood in terms of a strong k dependence of the gap Δ(k) which produces nodes on a Fermi-surface sheet with pronounced c-axis dispersion and deep minima on the remaining, quasi-two-dimensional sheets.

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  • Received 21 April 2010

DOI:https://doi.org/10.1103/PhysRevB.82.064501

©2010 American Physical Society

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Led by the nodes

Published 2 August 2010

Heat transport measurements in an iron-based superconductor offer new clues towards the determination of the superconducting pairing interaction in these materials.

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Authors & Affiliations

J.-Ph. Reid1, M. A. Tanatar2, X. G. Luo1, H. Shakeripour1, N. Doiron-Leyraud1, N. Ni2,3, S. L. Bud’ko2,3, P. C. Canfield2,3, R. Prozorov2,3, and Louis Taillefer1,4,*

  • 1Département de physique & RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1
  • 2Ames Laboratory, Ames, Iowa 50011, USA
  • 3Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
  • 4Canadian Institute for Advanced Research, Toronto, Ontario, Canada M5G 1Z8

  • *louis.taillefer@physique.usherbrooke.ca

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Issue

Vol. 82, Iss. 6 — 1 August 2010

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