Strongly bound yet light bipolarons for double-well electron-phonon coupling

Abstract

We use the momentum average approximation to study the ground-state properties of strongly bound bipolarons in the double-well electron-phonon (el-ph) coupling model, which describes certain intercalated lattices where the linear term in the el-ph coupling vanishes due to symmetry. We show that this model predicts the existence of strongly bound yet lightweight bipolarons in some regions of the parameter space. This provides an alternative mechanism for the appearance of such bipolarons, in addition to long-range el-ph coupling and special lattice geometries.