Spectroscopic study of bound magnetic polaron formation and the metal-semiconductor transition inEuB6

We present a Raman-scattering study of the metal-semiconductor transition in ${\mathrm{EuB}}_6.$ The metal-semiconductor (MS) transition in this compound manifests itself as a change from a diffusive electronic scattering response in the high-temperature paramagnetic phase, to a flat continuum scattering response in the low-temperature ferromagnetic metal phase which is characteristic of a strongly correlated metal. Most interesting is evidence that the MS transition in ${\mathrm{EuB}}_6$ is precipitated by the formation of bound magnetic polarons involving carriers bound to defects.