Physics – Condensed Matter – Superconductivity
Scientific paper
2009-04-26
Phys. Rev. B 80, 140503(R) (2009)
Physics
Condensed Matter
Superconductivity
Scientific paper
10.1103/PhysRevB.80.140503
The thermal conductivity $\kappa$ of the iron-arsenide superconductor Ba$_{1-x}$K$_x$Fe$_2$As$_2$ ($T_c \simeq$ 30 K) was measured in single crystals at temperatures down to $T \simeq 50$ mK ($\simeq T_c$/600) and in magnetic fields up to $H = 15$ T ($\simeq H_{c2}$/4). A negligible residual linear term in $\kappa/T$ as $T \to 0$ 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.
Bud'ko Sergey L.
Canfield Paul. C.
Doiron-Leyraud Nicolas
Luo Hui-qian
Luo X. G.
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