We present theoretical models, in one and two space dimensions, that exhibit Mott insulating ground states at fractional occupations without any symmetry breaking. The Hamiltonians of these models are non-local in configuration space, but local in phase space.
Cite
@article{arxiv.cond-mat/0309260,
title = {Mott Insulators Without Symmetry Breaking},
author = {Dung-Hai Lee and Jon Magne Leinaas},
journal= {arXiv preprint arXiv:cond-mat/0309260},
year = {2009}
}