The ab-plane thermal conductivity κ of single-crystalline hexagonal MgB_2 has been measured as a function of magnetic field H with orientations both parallel and perpendicular to the c-axis and at temperatures between 0.5 and 300 K. In the mixed state, κ(H) measured at constant temperatures reveals features that are not typical for common type-II superconductors. The observed behavior may be associated with the field-induced reduction of two superconducting energy gaps, significantly different in magnitude. A nonlinear temperature dependence of the electronic thermal conductivity is observed in the field-induced normal state at low temperatures. This behavior is at variance with the Wiedemann-Franz law, and suggests an unexpected instability of the electronic subsystem in the normal state at T ~ 1 K.
@article{arxiv.cond-mat/0201517,
title = {Thermal conductivity of single crystalline MgB_2},
author = {A. V. Sologubenko and J. Jun and S. M. Kazakov and J. Karpinski and H. R. Ott},
journal= {arXiv preprint arXiv:cond-mat/0201517},
year = {2009}
}