The superconducting gap structure of LaFePO (Tc=7.4K) is studied by thermal conductivity (κ) at low temperatures in fields H parallel and perpendicular to the c axis. A clear two-step field dependence of κ(H) with a characteristic field Hs(∼350 Oe) much lower than the upper critical field Hc2 is observed. In spite of large anisotropy of Hc2, κ(H) in both H-directions is nearly identical below Hs. Above Hs, κ(H) grows gradually with H with a convex curvature, followed by a steep increase with strong upward curvature near Hc2. These results indicate the multigap superconductivity with active two-dimensional (2D) and passive 3D bands having contrasting gap values. Together with the recent penetration depth results, we suggest that the 2D bands consist of nodal and nodeless ones, consistent with the extended s-wave symmetry.
@article{arxiv.0906.0622,
title = {Superconducting Gap Structure of LaFePO Studied by Thermal Conductivity},
author = {M. Yamashita and N. Nakata and Y. Senshu and S. Tonegawa and K. Ikada and K. Hashimoto and H. Sugawara and T. Shibauchi and Y. Matsuda},
journal= {arXiv preprint arXiv:0906.0622},
year = {2009}
}