The influence of nonlocal interactions on valence transitions and formation of excitonic bound states in the generalized Falicov–Kimball model
We use the density-matrix-renormalization-group (DMRG) method to study the combined effects of nonlocal interactions on valence transitions and the formation of excitonic bound states in the generalized Falicov–Kimball model. In particular, we consider the nearest-neighbour Coulomb interaction Unn between two d, two f, d and f electrons as well as the so-called correlated hopping term Uch and examine their effects on the density of conduction nd (valence nf) electrons and the excitonic momentum distribution N(q). It is shown that Unn and Uch exhibit very strong and fully different effects on valence transitions and the formation (condensation) of excitonic bound states. While the nonlocal interaction Unn suppresses the formation of zero momentum condensate (N(q = 0)) and stabilizes the intermediate valence phases with nd ~ 0.5, nf ~ 0.5, the correlated hopping term Uch significantly enhances the number of excitons in the zero-momentum condensate and suppresses the stability region of intermediate valence phases. The physically most interesting results are observed if both Unn and Uch are nonzero, when the combined effects of Unn and Uch are able to generate discontinuous changes in nf, N(q = 0) and some other ground-state quantities.
KeywordsSolid State and Materials
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