Field dependence of electronic thermal conductivity in multigap superconductors

We show that a steep increase observed in the low-field electronic thermal conductivity, kappa(s), of MgB2 is a special feature of multigap superconductors, when the mean free path becomes comparable to the coherence length of the smaller gap over its entire Fermi surface. In this regime, delocalization of quasiparticle excitations bound in vortex cores leads a rapid rise of kappa(s) at low magnetic fields. On the contrary, superclean samples should exhibit a weak field dependence of kappa(s) at low fields due to quasiparticle localization. A comparison to cases with a single anisotropic gap is also made. (C) 2004 Published by Elsevier B.V.