Optical properties of the magnetic semiconductor Eu₅In₂As₆

The temperature dependence of the reflectivity of the weakly correlated semiconductor Eu₅In₂As₆ (T_N ~ 16 K) has been measured over a wide frequency range and the optical conductivity determined from a Kramers-Kronig analysis.  The optical conductivity has a semiconducting character with an onset of absorption (optical gap) above about 60 meV, somewhat larger than the transport gap of about 45 meV; below this energy the optical conductivity is dominated by the normally infrared-active lattice modes.  At least 11 vibrational modes are identified.  The highest frequency mode, which occurs at ~200 cm^-1, also has the largest oscillator strength.  Evidence for phonon anomalies below T_N will be discussed.