Highly anisotropic gap function in borocarbide superconductor LuNi2B2C - art. no. 237001

The thermal conductivity of borocarbide superconductor LuNi2B2C was measure d down to 70 mK (T-c/200) in a magnetic field perpendicular to the heat cur rent from H = 0 to above H-c2 = 7 T. As soon as vortices enter the sample, the conduction at T --> 0 grows rapidly, showing unambiguously that delocal ized quasiparticles are present at the lowest energies. The field dependenc e is very similar to that Of UPt3, a heavy-fermion superconductor with a li ne of nodes in the gap, and very different from the exponential dependence characteristic of s-wave superconductors. This is strong evidence for a hig hly anisotropic gap function in LuNi2B2C, possibly with nodes.