Germanene

In this chapter a brief review of the current status of germanene, that is, the germanium analog of graphene, is given. Germanene shares many properties with its carbon counterpart. There are, however, also a few differences between germanene and graphene. Theory predicts that the honeycomb lattice of freestanding germanene is not fully planar, like graphene, but slightly buckled, that is, the two interpenetrating triangular sublattices are slightly displaced with respect to each other in a direction normal to the germanene sheet. Despite this buckling the dispersion relation of the low-energy bands at the K and K′ points of the surface Brillouin zone of germanene are still linear, implying that the material hosts Dirac fermions. The buckling of germanene allows to open a bandgap by transferring charge from one triangular sublattice to the other triangular sublattice. In addition, germanene also has a substantially larger spin-orbit gap (~ 24meV) than graphene (~ a few μeVs) owing to its much larger atomic number. This relatively large spin-orbit gap of germanene makes this two-dimensional Dirac material the ideal candidate to verify the existence of the quantum spin Hall effect.