  Silicene is a buckled monolayer of silicon. Its electronic properties are
distinct from both the conventional two dimensional electron gas and the famous
graphene due to strong spin orbit interaction and the buckled structure.
Silicene has the potential to overcome limitations encountered for graphene, in
particular the zero band gap and weak spin orbit interaction. We find for
silicene a valley polarized quantum Hall effect and topological insulator phase
transitions. We use the Kubo formalism to discuss the Hall conductivity and
address the longitudinal conductivity for elastic impurity scattering in the
first Born approximation. We show that the combination of an electric field
with intrinsic spin orbit interaction leads to quantum phase transitions at the
charge neutrality point. This provides a tool to experimentally tune the
topological state of silicene. In contrast to graphene and other conventional
topological insulators, the effects in silicene are experimentally accessible.
Therefore, silicene constitutes a model system for exploring the spin and
valley physics not accessible in graphene due to the small spin orbit
interaction.
