Field-Induced Free-Electron Carriers in Graphite

First-principles calculations show that free-electron carriers are induced in a few-layer graphite by applying an external electric field normal to the graphene plane. The electric field substantially shifts the nearly free electron (NFE) states downward, and the states are not distributed at atomic sites but in spacious regions in graphite. The NFE state finally crosses the Fermi level under an electric field of about 0.5 V/Å. It is found that the threshold voltage resulting in free-electron carriers monotonically decreases with increasing number of layers. This indicates the possibility of field-induced superconductivity in all carbon materials even without chemical doping.