Ferromagnetism was recently observed at unexpectedly high temperatures in La-doped CaB_6. The starting point of all theoretical proposals to explain this observation is a semimetallic electronic structure calculated for CaB_6 within the local density approximation. Here we report the results of parameter-free quasiparticle calculations of the single-particle excitation spectrum which show that CaB_6 is not a semimetal but a semiconductor with a band gap of 0.8 eV. Magnetism in La_xCa_{1-x}B_6 occurs just on the metallic side of a Mott transition in the La-induced impurity band.
@article{arxiv.cond-mat/0011109,
title = {CaB_6: a new semiconducting material for spin electronics},
author = {H. J. Tromp and P. van Gelderen and P. J. Kelly and G. Brocks and P. A. Bobbert},
journal= {arXiv preprint arXiv:cond-mat/0011109},
year = {2016}
}