Effects of correlated hopping on electronic ferroelectricity in the extended Falicov-Kimball model in two dimensions

Abstract

We use the Hartree-Fock (HF) approximation with the charge-density-wave (CDW) instability to study the effect of correlated hopping on the stability of electronic ferroelectricity in the extended Falicov-Kimball model (FKM) in two dimensions. It is shown that the effects of correlated hopping term are very strong, especially for negative values of the $f$-level energy $E_f$, where they lead to: (i) stabilization of the ferroelectric ground state with a spontaneous hybridization $P_{df}=\langle d^+f \rangle$ for positive values of correlated hopping parameter $t'_d$, (ii) stabilization of the antiferroelectric phase for $t'_d < t'_{d,crit.} < 0$ and (iii) suppression of the ferroelectric ground state for $t'_{d,crit.} \leqslant t'_d < 0$, The effects of correlated hopping on valence transitions are also discussed.