Evl. Demello et J. Ranninger, QUASI-PARTICLE PROPERTIES OF SMALL POLARONS AND BIPOLARONS, Physical review. B, Condensed matter, 58(14), 1998, pp. 9098-9103
The question to what extent small polarons and bipolarons can exist as
well-defined itinerant quasiparticles is examined in terms of their s
pectral functions. Although in a certain regime of the parameter space
of the electron-lattice coupling and adiabaticity ratio, such polaron
ic quasiparticles can in principle exist as itinerant states, we show
that their bandwidth is so small that their formation in real material
s is most unlikely. Outside this parameter regime where such potential
ly itinerant states are theoretically possible, we show that their res
idual interaction with the lattice vibrations and/or with each other l
eads to a dynamical dephasing between the charge carriers and the loca
l lattice deformations surrounding them and hence destroys any such it
inerant quasiparticle features. The conjectures made here are meant to
serve as a guideline to interpret experimental investigations using p
hotoemission spectroscopy and are tested theoretically on the basis of
small clusters using exact diagonalization studies. [S0163-1829(98)05
038-3].