  We propose new topological insulators in hexagonal wurtzite-type binary
compounds based on the first principles calculations. It is found that two
compounds AgI and AuI are three-dimensional topological insulators with a
naturally opened band-gap at Fermi level. From band inversion mechanism point
view, this new family of topological insulators is similar with HgTe, which has
s (Gamma 6) - p (Gamma 8) band inversion. Our results strongly support that the
spin-orbit coupling is not an essential factor to the band inversion mechanism;
on the contrary, it is mainly responsible to the formation of a global band gap
for the studied topological insulators. We further theoretically explore the
feasibility of tuning the topological order of the studied compounds with two
types of strains. The results show that the uniaxial strain can contribute
extremely drastic impacts to the band inversion behavior, which provide an
effective approach to induce topological phase transition.
