Nodes in the gap structure of the iron arsenide superconductor Ba(Fe1−xCox)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, Louis Taillefer
DOI 10.1103/PhysRevB.82.064501 · Physical Review B
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Abstract
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.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 9.7 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 14.4 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 13.7 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 17.2 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 22.9 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 24.1 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 15.2 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 14.6 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 11 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 8.4 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 9.3 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 13 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 14.2 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 16.7 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 22.2 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 14.8 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 10.8 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 10.2 | Pressure not reported | zero_resistance |
| Ba(Fe1-xCox)2As2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 8.2 | Pressure not reported | zero_resistance |
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