Electronic properties of two-dimensional hexagonal germanium

The electronic properties of two-dimensional hexagonal germanium, so called germanene, are investigated using first-principles simulations. Consistent with previous reports, the surface is predicted to have a poor metallic behavior, i.e., being metallic with a low density of states at the Fermi level. It is found that biaxial compressively strained germanene is a gapless semiconductor with linear energy dispersions near the K points-like graphene. The calculated Fermi velocity of germanene is almost independent of the strain and is about 1.7x10(6) m/s, quite comparable to the value in graphene.