title: Order by disorder in the antiferromagnetic Ising model on an elastic triangular lattice.
abstract: Geometrically frustrated materials have a ground-state degeneracy that may be lifted by subtle effects, such as higher-order interactions causing small energetic preferences for ordered structures. Alternatively, ordering may result from entropic differences between configurations in an effect termed order by disorder. Motivated by recent experiments in a frustrated colloidal system in which ordering is suspected to result from entropy, we consider in this paper the antiferromagnetic Ising model on a deformable triangular lattice. We calculate the displacements exactly at the microscopic level and, contrary to previous studies, find a partially disordered ground state of randomly zigzagging stripes. Each such configuration is deformed differently and thus has a unique phonon spectrum with distinct entropy, lifting the degeneracy at finite temperature. Nonetheless, due to the free-energy barriers between the ground-state configurations, the system falls into a disordered glassy state.
authors: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel. yair.shokef@weizmann.ac.il
authors: Yair
authors: Y
authors: Shokef
authors: Anton
authors: A
authors: Souslov
authors: T C
authors: TC
authors: Lubensky
mesh_terms: D019277:Entropy; D007501:Iron / Q000737:chemistry*; D008280:Magnetics; D008962:Models, Theoretical; D013696:Temperature
chemical_list: D007501:Iron