The electron hole asymmetry has been measured in natural graphite using magneto-optical absorption measurements. A splitting is observed for the transitions at both the K-point and the H-point of the Brillouin zone of graphite where the effect of trigonal warping vanishes. This result is fully consistent with the SWM Hamiltonian providing the free electron kinetic energy terms are taken into account. An identical electron-hole asymmetry should be present in graphene.
@article{arxiv.1111.2676,
title = {The origin of electron-hole asymmetry in graphite},
author = {P. Plochocka and P. Y. Solane and R. J. Nicholas and J. M. Schneider and B. A. Piot and D. K. Maude and O. Portugall and G. L. J. A. Rikken},
journal= {arXiv preprint arXiv:1111.2676},
year = {2011}
}