  Fluctuations of Hamiltonian eigenfunctions, measured by the inverse
participation ratio (IPR), turn out to characterize topological-band insulator
transitions occurring in 2D Dirac materials like silicene, which is
isostructural with graphene but with a strong spin-orbit interaction. Using
monotonic properties of the IPR, as a function of a perpendicular electric
field (which provides a tunable band gap), we define topological-like quantum
numbers that take different values in the topological-insulator and
band-insulator phases.
