Hybridization gap-open in CeIn3

Reflectivity spectra of CeIn₃ are measured at 7, 30, 50, 100, 150, 200 and 300 K in wild energy regions from 6 meV to 30 eV. Optical conductivity spectra are obtained from a Kramers–Kronig’ relation. A hump in the optical conductivity σ₁ is observed at about 500 cm⁻¹ below 100 K, resulting from strong hybridization between conduction electrons and Ce 4f electronic states. The low frequency plasmon indicating the existence of heavy particles is also observed below coherence temperature T^*  100 K.