Title: Phonon-mediated repulsion, sharp transitions and (quasi)self-trapping in the extended Peierls-Hubbard model,
Abstract: We study two identical fermions, or two hard-core bosons, in an infinite
chain and coupled to phonons by interactions that modulate their hopping as
described by the Peierls/Su-Schrieffer-Heeger (SSH) model. We show that
exchange of phonons generates effective nearest-neighbor repulsion between
particles and also gives rise to interactions that move the pair as a whole.
The two-polaron phase diagram exhibits two sharp transitions, leading to light
dimers at strong coupling and the flattening of the dimer dispersion at some
critical values of the parameters. This dimer (quasi)self-trapping occurs at
coupling strengths where single polarons are mobile. This illustrates that,
depending on the strength of the phonon-mediated interactions, the coupling to
phonons may completely suppress or strongly enhance quantum transport of
correlated particles.