Optical spectroscopy and electronic band structure of ferromagnetic EuB6

We present an optical conductivity of EuB6 over a wide range 2 meV–5.5 eV from reflectivity and ellipsometry measurements. Upon the ferromagnetic transition at Tc=15.5 K, interband transition 1 decreases below =3.3 eV and the lost spectral weight is transferred to the Drude 1 at 0.33 eV. Further a high-energy optical peak at around 4 eV exhibits a large splitting below Tc. We explain these high-energy 1 changes, that is, spectral-weight recovery and peak splitting, using local-density approximation+U band-structure calculations. Our finding suggests strongly that: 1 EuB6 is a semimetal and 2 the exchangedriven band splitting is the primary source of the drastic p 2 change at T Tc.