Effects of Y substitution on the electronic structure and charge dynamics of SmS
Abstract
Evolution of the electronic state by Y doping was explored by optical conductivity covering a wide energy and compositional region deduced from systematic reflectivity measurements of Sm1 -xYxS single crystals. Although electrons doped onto the 5 d band by Y dopants immediately realize a metallic state, the charge dynamics do not obey a simple Drude response and the spectral intensity is condensed in the mid-infrared region. Contrary to the pressure-induced case, a metallic phase appears in a certain compositional region before reaching the valence transition. The Fermi level is shifted upwards by electron doping. Therefore, the 5 d band must overlap with the weakly dispersive 4 f band more deeply than in the pressure-induced case to reach the valence transition, which can explain the stability of the divalent phase up to higher temperatures in the doped system than in the pressure-induced case. The present optical study provides us with a strategy that sulfur deficiency might increase operating temperature of negative thermal expansion in this system.
- Publication:
-
Physical Review B
- Pub Date:
- December 2019
- DOI:
- 10.1103/PhysRevB.100.245143
- Bibcode:
- 2019PhRvB.100x5143Y