P. Choudhury et An. Das, POLARONS AND BIPOLARONS IN A 4-SITE PERIODIC CHAIN OF SPINLESS FERMIONS, Physical review. B, Condensed matter, 53(6), 1996, pp. 3203-3210
The nature of polarons is studied in a four-site model containing one
and two spinless fermions in the presence of fermion-phonon (f-ph) int
eractions and intersite hopping. In the four-site one-fermion model a
small-to-large polaron transition associated with a sudden increase in
polaronic hopping and a decrease in the polaronic binding energy is o
bserved as the f-ph strength decreases below a particular value. The r
ole of the modified Lang-Firsov transformation and two-phonon coherent
states In lowering the energy of the system is discussed. For the fou
r-site two-fermion system the nature and stability of bipolaronic stat
es with the variation of f-ph coupling strength are studied. It is obs
erved that bipolaronic states are stable only in the presence of inter
site f-ph interactions.