Origin of the black-golden transition in Sm1-xYxS

Abstract

We report angle-resolved photoemission spectroscopy, electrical resistivity and Hall effect measurements on Sm1-xYxS. At the smallest doping concentration x 0.03, the system changes from a semiconducting to metallic conductivity, whereas it is at a critical concentration xc ≃ 0.19 that there occurs the volume collapse accompanied by a color change from black to golden. It appears that the band gap between 4f and 5d bands vanishes at xc. From these results, we suggest that the black-to-golden transition of Sm1-xYxS has the same mechanism as the pressure-induced valence transition of SmS, but the semiconductor-to-metal transition has a different origin for Sm1-xYxS and SmS.