Large Bipolaron in a Polaron-Gas Background

A criterion, proposed by the present authors, is used to derive numerical results for the stability of a large bipolaron embedded in a polaron gas. The main conclusion is that an isolated metastable bipolaron can be stabilized by the polaron gas surroundings because of the Fermi statistics of polarons. On the other hand, it is found that the exchange interaction tends to destabilize the bipolaron. The study is performed both for bulk (3D) materials and for thin (2D) films within the Hartree-Fock approximation. The bipolaron is described by an extension of the Feynman