Combined effects of local and nonlocal hybridization on formation and condensation of excitons in the extended Falicov-Kimball model

Abstract

We study the combined effects of local and nonlocal hybridization on the formation and condensation of the excitonic bound states in the extended FalicovKimball model by the density-matrix-renormalization-group (DMRG) method. Analysing the resultant behaviours of the excitonic momentum distribution N (q) we found, that unlike the local hybridization V , which supports the formation of the q = 0 momentum condensate, the nonlocal hybridization V n supports the formation of the q = π momentum condensate. The combined effect of local and nonlocal hybridization further enhances the excitonic correlations in q = 0 as well as q = π state, especially for V and V n values from the charge-density-wave (CDW) region. Strong effects of local and nonlocal hybridization are observed also for other ground-state quantities of the model such as the f -electron density, or the density of unbound d-electrons, which are generally enhanced with increasing V and V n . The same calculations performed for nonzero values of f -level energy E f revealed that this model can yield a reasonable explanation for the pressure-induced resistivity anomaly observed experimentally in T mSe 0.45 T e 0.55 compound.

The influence of nonlocal interactions on valence transitions and formation of excitonic bound states in the generalized Falicov–Kimball model

“…The first one strongly supports the formation of condensate, while the second one destroys it completely. In systems with equal parity orbitals, the local and nonlocal hybridization can coexist and for this case we have found [22] that the combined effect of both hybridizations strongly support the formation of zero-momentum condensate the existence of which can yield the reasonable explanation for the pressure-induced resistivity anomaly observed experimentally in T mSe 0.45 T e 0.55 compound [23].…”

DMRG study of exciton condensation in the extended Falicov-Kimball model

“…In this article we focus our attention on the properties of the EI phase induced by local hybridization V in the one dimension. Although it is generally known that there is no nonvanishing P d f = d + f expectation value in the limit of vanishing hybridization (no spontaneous hybridization), the studies that we performed in the past years on various extensions of the original Falicov-Kimball model showed that it is possible to dramatically enhance excitonic correlations in the limit of small, but finite V by additional interactions/factors [36][37][38][39]. The effects of most important interactions are discussed in this review.…”

“…In this situation, the most promising candidates for studying this phenomenon seem to be the systems with equal parity of d and f orbitals, where the nonlocal hybridization H n can be written as [38]:…”

“…, the nonlocal hybridization V n favors the staggered Ising-type ordering along the x direction, while V favors a uniform polarization along the x direction and the staggered Ising-type ordering along the y direction. In our paper [38] we have examined the model for arbitrary V and V n and unlike the paper of Zenker et al [44] we have focused our attention primarily on a description of process of formation and condensation of exitonic bound states.…”

“…(Colour online) The density of zero-momentum excitons n 0 (a), the density of π-momentum excitons n π (b), the total d-electron density n d (c), and the total density of unbound d electrons n un d = n d − n T (d) as functions of E f calculated for U = 4, V = 0.2, L = 60 and six different values of V n[38].…”