There are two classes of Mott insulators in nature, distinguished by their responses to weak doping. With increasing chemical potential, Type I Mott insulators undergo a first order phase transition from the undoped to the doped phase. In the presence of long-range Coulomb interactions, this leads to an inhomogeneous state exhibiting ``micro-phase separation.'' In contrast, in Type II Mott insulators charges go in continuously above a critical chemical potential. We show that if the insulating state has a broken symmetry, this increases the likelihood that it will be Type I. There exists a close analogy between these two types of Mott insulators and the familiar Type I and Type II superconductors.
@article{arxiv.cond-mat/0208536,
title = {The types of Mott insulator},
author = {Dung-Hai Lee and Steven A. Kivelson},
journal= {arXiv preprint arXiv:cond-mat/0208536},
year = {2009}
}