An extended Falicov-Kimball model on a triangular lattice

¹ Department of Physics, Indian Institute of Technology Roorkee - Roorkee 247667, Uttarakhand, India
² Department of Physics and Centre for Theoretical Studies, Indian Institute of Technology Kharagpur Kharagpur-721302, India

^a tulimfph@iitr.ernet.in

Received: 12 August 2010
Accepted: 3 February 2011

Abstract

The combined effect of frustration and correlation in electrons is a matter of considerable interest lately. In this context a Falicov-Kimball model on a triangular lattice with two localized states, relevant for certain correlated systems, is considered. Making use of the local symmetries of the model, our numerical study reveals a number of orbital ordered ground states, tuned by the small changes in parameters while quantum fluctuations between the localized and extended states produce homogeneous mixed valence. The inversion symmetry of the Hamiltonian is broken by most of these ordered states leading to orbitally driven ferroelectricity. We demonstrate that there is no spontaneous symmetry breaking when the ground state is inhomogeneous. The study could be relevant for frustrated systems like GdI₂, NaTiO₂ (in its low-temperature C2/m phase) where two Mott localized states couple to a conduction band.