Two-dimensional electron and hole gases at the surface of graphite

We report two-dimensional (2D) electron and hole gases induced at the surface of graphite by the electric field effect. The 2D gases reside within a few near-surface atomic layers and exhibit mobilities up to 15 000 and $60000{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ at room and liquid-helium temperatures, respectively. The mobilities imply ballistic transport on $\mu \mathrm{m}$ scale. Pronounced Shubnikov–de Haas oscillations reveal the existence of two types of charge carries in both electron and hole gases.