title: Directional ordering of fluctuations in a two-dimensional compass model.
abstract: In the Mott insulating phase of the transition metal oxides, the effective orbital-orbital interaction is directional both in orbital space and in real space. We discuss a classical realization of directional coupling in two dimensions. Despite extensive degeneracy of the ground state, the model exhibits partial orbital ordering in the form of directional ordering of fluctuations at low temperatures stabilized by an entropy gap. Transition to the disordered phase is shown to be in the Ising universality class through exact mapping and multicanonical Monte Carlo simulations.
authors.affiliation: Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221-0011, USA.
authors.forename: Anup
authors.initials: A
authors.lastname: Mishra
authors.forename: Michael
authors.initials: M
authors.lastname: Ma
authors.forename: Fu-Chun
authors.initials: FC
authors.lastname: Zhang
authors.forename: Siegfried
authors.initials: S
authors.lastname: Guertler
authors.forename: Lei-Han
authors.initials: LH
authors.lastname: Tang
authors.forename: Shaolong
authors.initials: S
authors.lastname: Wan