Phase transitions in the generalized spin-one-half Falicov–Kimball model in two dimensions

Abstract

The extrapolation of small-cluster exact-diagonalisation calculations and the Monte-Carlo method is used to study the spin-one-half Falicov–Kimball model extended by the spin-dependent Coulomb interaction (J) between the localized f and itinerant d electrons as well as the on-site Coulomb interaction (U _ff ) between the localized f electrons. It is shown that in the symmetric case the ground-state phase diagram of the model has an extremely simple structure that consists of only two phases, and namely, the charge-density-wave (CDW) phase and the spin-density-wave (SDW) phase. The nonzero temperature studies showed that these phases persist also at finite temperatures. The critical temperature T _c for a transition from the low-temperature ordered phases to the high-temperature disordered phase is calculated numerically for various values of J and U _ff .

Keywords:

• Falicov–Kimball model
• strongly correlated electrons
• charge and spin ordering
• thermodynamics

Acknowledgements

This work was supported by Slovak Grant Agency VEGA under Grant No. 2/7057/27 and Slovak Research and Development Agency (APVV) under Grants LPP-0047-06. H. Čenčariková acknowledges support of Stefan Schwartz Foundation.