Large bipolaron in one- and two-dimensional systems

The bound state of two electrons in polar crystals is investigated in various dimensional systems by numerical solution of the Bethe-Salpeter equation in which the interaction is composed of the Coulomb repulsion and the attractive interaction mediated by longitudinal, polar-optic phonons. In three-dimensional (3D) systems, no bound state is found, while in both 1D and 2D systems a bound state exists. In particular, in 1D systems, the binding energy can be of the order of the energy of the longitudinal-optic phonon (although the binding radius is large compared to the lattice constant).