Pairing in a generalized Holstein model for small polarons

Phys.Lett. A 168, 305 (1992).

We consider a generalization of the Holstein model for small polarons: the lattice deformation is assumed to have a non-linear dependence on the electron site occupation. It is shown that the non-linearity leads to a particle-hole asymmetric Hamiltonian and to pairing in certain parameters ranges. A signature of this pairing mechanism is that spectral weight in the frequency-dependent conductivity is transfered from high to low frequencies when pairing occurs; the physical origin of this effect is discussed.