%0 Journal Article
%T Optical spectroscopy study on the electronic structure of $Eu_{1-x} Ca_x B_6$
%A Jungho Kim
%A S. -J. Oh
%A Youngwoo Lee
%A E. J. Choi
%A C. C. Homes
%A Jong-Soo Rhyee
%A B. K. Cho
%J Physics
%D 2004
%I arXiv
%R 10.1103/PhysRevB.71.075105
%X The optical conductivity $\sigma_{1}(\omega)$ of Eu$_{1-x}$Ca$_{x}$B$_{6}$ has been obtained from reflectivity and ellipsometry measurements for series of compositions, $0\leq x\leq 1$. The interband part of $\sigma_{1}(\omega) $ shifts continuously to higher frequency as Ca-content $x$ increases. Also the intraband spectral weight of $\sigma_{1}(\omega)$ decreases rapidly and essentially vanishes for $x\geq x_{c}=0.35$. These results show that the valence band and the conduction band of Eu$_{1-x}$Ca$_{x}$B$_{6}$ move away from each other such that their band overlap decreases with increasing Ca-substitution. As a result, the electronic state evolves from the semimetallic structure of EuB$_{6}$ to the insulating CaB$_{6}$ where the two bands are separated to open a finite gap ($\simeq 0.25$ eV) at the X-point of the Brillouin zone.
%U http://arxiv.org/abs/cond-mat/0409104v1