Using a hybrid method based on fermionic diagonalization and classical Monte Carlo, we investigate the interplay between itinerant and localized spins, with competing double- and super-exchange interactions, on a honeycomb lattice. For moderate superexchange, a geometrically frustrated triangular lattice of hexagons forms spontaneously. For slightly larger superexchange a dimerized groundstate is stable that has macroscopic degeneracy. The presence of these states on a non-frustrated honeycomb lattice highlights a novel phenomenon in this itinerant electron system: emergent geometrical frustration and degeneracy.
@article{arxiv.1105.2469,
title = {Macroscopic Degeneracy and Emergent Frustration in a Honeycomb Lattice Magnet},
author = {Jörn W. F. Venderbos and Maria Daghofer and Jeroen van den Brink and Sanjeev Kumar},
journal= {arXiv preprint arXiv:1105.2469},
year = {2011}
}