Coexistence of large and small mass polarons

The polaron self-energy and the effective mass are studied around the Γ point of the Brillouin zone as a function of the bare electron band width Δ, the electron-phonon coupling constant α, and the density λ of other electrons. It is found that there are ranges of values of Δ, α and λ in which there is coexistence of polarons with small and large masses. The effect of such coexistence on the optical infrared absorbtion coefficient in polar materials is discussed.