@article{10_1090_S0894_0347_2012_00745_0,
     author = {Fefferman, Charles and Weinstein, Michael},
     title = {Honeycomb lattice potentials and {Dirac} points},
     journal = {Journal of the American Mathematical Society},
     pages = {1169--1220},
     publisher = {mathdoc},
     volume = {25},
     number = {4},
     year = {2012},
     doi = {10.1090/S0894-0347-2012-00745-0},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-2012-00745-0/}
}