Influence of ƒ-electron Hopping On Valence Transition of Mixed-Valent Systems

The contribution of ƒ-electron hopping has been studied on a four-site square cluster in an exact diagonalization method using extended Falicov-Kimball model. It appears that ƒ-ƒ hopping shifts the critical ƒ-level energy (Ec) at which valence transition occurs. So far entropy is concerned, ƒ-ƒ hopping increases disorder in the system. Both, single and double-peak structures are obtained in specific heat curves. The peak height decreases with higher negativity of ƒ-electron hopping. That indicates a reduction in the number of the density of states. Spin susceptibility (χ) characteristics show Curie-like nature as well as antiferromagnetic ordering which grows with ƒ-ƒ hopping.