Abstract
The thermal conductivity of the iron-arsenide superconductor was measured down to 50 mK for a heat current parallel and perpendicular to the tetragonal axis for seven Co concentrations from underdoped to overdoped regions of the phase diagram . A residual linear term is observed in the limit when the current is along the axis, revealing the presence of nodes in the gap. Because the nodes appear as moves away from the concentration of maximal , they must be accidental, not imposed by symmetry, and are therefore compatible with an state, for example. The fact that the in-plane residual linear term is negligible at all implies that the nodes are located in regions of the Fermi surface that contribute strongly to -axis conduction and very little to in-plane conduction. Application of a moderate magnetic field (e.g., ) excites quasiparticles that conduct heat along the axis just as well as the nodal quasiparticles conduct along the 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 dependence of the gap which produces nodes on a Fermi-surface sheet with pronounced -axis dispersion and deep minima on the remaining, quasi-two-dimensional sheets.
6 More- Received 21 April 2010
DOI:https://doi.org/10.1103/PhysRevB.82.064501
©2010 American Physical Society
Viewpoint
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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