Quasiparticle heat transport in single-crystalline Ba(1-x)KxFe(2)As(2): Evidence for a k-dependent superconducting gap without nodes
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Physics and Astronomy
The thermal conductivity kappa of the iron-arsenide superconductor Ba1-xKxFe2As2 (T-c similar or equal to 30 K) was measured in single crystals at temperatures down to T not similar or equal to 50 mK (similar or equal to T-c/600) and in magnetic fields up to H = 15 T(similar or equal to H-c2/4). A negligible residual linear term in kappa/T as T -> 0 shows that there are no zero-energy quasiparticles in the superconducting state. This rules out the existence of line and in-plane point nodes in the superconducting gap, imposing strong constraints on the symmetry of the order parameter. It excludes d-wave symmetry, drawing a clear distinction between these superconductors and the high-T-c cuprates. However, the fact that a magnetic field much smaller than H-c2 can induce a residual linear term indicates that the gap must be very small on part of the Fermi surface, whether from strong anisotropy or band dependence, or both.
This article is published as Luo, X. G., M. A. Tanatar, J-Ph Reid, H. Shakeripour, N. Doiron-Leyraud, N. Ni, S. L. Bud’Ko et al. "Quasiparticle heat transport in single-crystalline Ba 1− x K x Fe 2 As 2: Evidence for a k-dependent superconducting gap without nodes." Physical Review B 80, no. 14 (2009): 140503. DOI: 10.1103/PhysRevB.80.140503. Copyright 2009 American Physical Society. Posted with permission.