In fractionally filled Landau levels there is only a small energy difference between broken translational symmetry electron-crystal states and exotic correlated quantum fluid states. We show that the spatially periodic substrate interaction associated with the long period moir\'{e} patterns present in graphene on nearly aligned hexagonal boron nitride (hBN) tilts this close competition in favor of the former, explaining surprising recent experimental findings.
@article{arxiv.1605.07138,
title = {Fractional Hofstadter States in Graphene on Hexagonal Boron Nitride},
author = {Ashley M. DaSilva and Jeil Jung and Allan H. MacDonald},
journal= {arXiv preprint arXiv:1605.07138},
year = {2016}
}