Quasiparticle heat transport in single-crystalline Ba1−xKxFe2As2: Evidence for a k-dependent superconducting gap without nodes

Abstract

The thermal conductivity κ of the iron-arsenide superconductor Ba1−xKxFe2As2(Tc≃30 K) was measured in single crystals at temperatures down to T≃50 mK(≃Tc/600) and in magnetic fields up to H=15 T(≃Hc2/4). A negligible residual linear term in κ/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-Tc cuprates. However, the fact that a magnetic field much smaller than Hc2 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.

Source-reported materials — not catalogue approval

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