Resonant scattering and optical properties of intermediate valence Sm_1-xY_xS

The intermediate-valence state of Sm in Sm1-xYxS has been investigated in terms of the d.c. and optical scattering time of the conduction electrons. Strong resonant scattering in the collapsed metallic phase is attributed to the pinning of the Fermi level EF within a mixed-configuration resonant state. The composition- and temperature dependent electronic phase transition is found to occur when EF reaches the resonant state. © 1976.