Abstract
Temperature dependence of absorption spectra for thin films of doped manganites where is a rare-earth atom, has been investigated by systematically changing the averaged ionic radius of perovskite site. We have observed a specific absorption band at due to optical excitations from small polarons (SP). Spectral weight of the SP band increases with decreasing temperature and eventually disappears at the insulator-metal transition, indicating that SP in the paramagnetic state changes into bare electrons (or large polarons) in the ferromagnetic state due to the enhanced one-electron bandwidth We further derived important physical quantities, i.e., on-site exchange interaction and binding energy of SP, and discuss the material dependence of the stability of SP.
- Received 17 February 1998
DOI:https://doi.org/10.1103/PhysRevB.58.R4281
©1998 American Physical Society