Campus Units

Physics and Astronomy, Ames Laboratory

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Publication Version

Published Version

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Journal or Book Title

Physical Review B





First Page





The thermal conductivity κ of the iron-arsenide superconductor Ba(Fe1−xCox)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 (0.038≤x≤0.127). A residual linear term κc0/T is observed in the T→0 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.


This article is published as Reid, J-Ph, M. A. Tanatar, X. G. Luo, H. Shakeripour, N. Doiron-Leyraud, Ni Ni, S. L. Bud’ko, P. C. Canfield, R. Prozorov, and Louis Taillefer. "Nodes in the gap structure of the iron arsenide superconductor Ba (Fe 1− x Co x) 2 As 2 from c-axis heat transport measurements." Physical Review B 82, no. 6 (2010): 064501. DOI: 10.1103/PhysRevB.82.064501. Posted with permission.

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American Physical Society



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