Formation of Fröhlich bipolarons

Abstract

The binding energy of a bipolaron is calculated by the variational method as a function of the Fröhlich coupling constant α and η=${\epsilon }_{\infty }$/${\epsilon }_0$, where ${\epsilon }_{\infty }$ (${\epsilon }_0$) is the optic (static) dielectric constant. It is found that the system of two equally charged polarons is stable in a broad region of α and η. Since α and η for strongly ionic crystals take on values close to this region, the possibility of experimental evidence for Fröhlich bipolarons is suggested. The estimated average electron-electron separation for the bound state takes on values between 0.2 and 1.0 polaron radius.