THE ELECTRONIC STRUCTURE OF YbCu4In AS OBSERVED THROUGH OPTICAL MEASUREMENTS

he intermetallic compound YbCu4In is an almost unique (except for metallic cerium) material exhibiting a first-order temperature-induced valence transition. At about 40-60 K all the physical properties show a sudden change, whereas no distortion of the crystal structure occurs. The optical response does not make an exception to this trend and an abrupt change in the optical functions at low temperatures is presented here. The spectra are discussed by taking into account some recent band structure calculations