Binding Energies, Effective Masses and Screenings Effects of Fröhlich Bipolarons

Abstract

The bipolaron ground state binding energy and the effective masses are calculated self-consistently in a scheme where the electron-phonon interaction is described by the Fröhlich interaction. We explicitly use the total linear momentum conservation and both two-and three-dimensional systems are considered. We review results for binding energies and show that the bipolaron effective mass increases with the electron-phonon coupling constant α more rapidly than two free polaron masses. As expected, the increase is greater in two than in three dimensions.We estimate the screening effects due to an electronic or hole density n in a range of values such that nR2b ≪ 1 (here Rb is the bipolaron radius). We find that the bipolaron binding energy decreases with n and eventually becomes positive indicating the existence of a metastable bipolaron state.Finally we discuss the possible connections between our results and high Tc superconductivity.