We show that the twisted graphene bilayer can reveal unusual topological properties at low energies, as a consequence of a Dirac-point splitting. These features rely on a symmetry analysis of the electron hopping between the two layers of graphene and we derive a simplified effective low-energy Hamiltonian which captures the essential topological properties of twisted bilayer graphene. The corresponding Landau levels peculiarly reveal a degenerate zero-energy mode which cannot be lifted by strong magnetic fields.
@article{arxiv.1103.3172,
title = {Topologically Protected Zero Modes in Twisted Bilayer Graphene},
author = {R. de Gail and M. O. Goerbig and F. Guinea and G. Montambaux and A. H. Castro Neto},
journal= {arXiv preprint arXiv:1103.3172},
year = {2011}
}