Formation of Fröhlich bipolarons

Abstract

The binding energy of a bipolaron is calculated by the variational method as a function of the Fr\"ohlich coupling constant \ensuremath{\alpha} and \ensuremath{\eta}=${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$/${\ensuremath{\epsilon}}_{0}$, where ${\ensuremath{\epsilon}}_{\ensuremath{\infty}}$ (${\ensuremath{\epsilon}}_{0}$) is the optic (static) dielectric constant. It is found that the system of two equally charged polarons is stable in a broad region of \ensuremath{\alpha} and \ensuremath{\eta}. Since \ensuremath{\alpha} and \ensuremath{\eta} for strongly ionic crystals take on values close to this region, the possibility of experimental evidence for Fr\"ohlich bipolarons is suggested. The estimated average electron-electron separation for the bound state takes on values between 0.2 and 1.0 polaron radius.