Optical spectroscopy and electronic band structure of ferromagnetic EuB(6)

Abstract

We present an optical conductivity of EuB(6) over a wide range (2 meV-5.5 eV) from reflectivity and ellipsometry measurements. Upon the ferromagnetic transition at T(c)=15.5 K, interband transition sigma(1)(omega) decreases below omega=3.3 eV and the lost spectral weight is transferred to the Drude sigma(1)(omega) at omega < 0.33 eV. Further a high-energy optical peak at around 4 eV exhibits a large splitting below T(c). We explain these high-energy sigma(1)(omega) changes, that is, spectral-weight recovery and peak splitting, using local-density approximation+U band-structure calculations. Our finding suggests strongly that: (1) EuB(6) is a semimetal and (2) the exchange-driven band splitting is the primary source of the drastic omega(2)(p) change at T < T(c).