Realizing robust large-gap quantum spin Hall state in 2D HgTe monolayer on insulating substrate

Although many possible two-dimensional (2D) topological insulators (TIs) have been predicted in recent years, there is still lack of experimentally realizable 2D TI. Through first-principles and tight-binding simulations, we found an effective way to stabilize the robust quantum spin Hall state with a large nontrivial gap of 227 meV in 2D honeycomb HgTe monolayer by the Al$_2$O$_3$(0001) substrate. The band topology originates from the band inversion between the $s-$like and $p-$like orbitals that are contributed completely by the Hg and Te atoms, so the quantized edge states are restricted within the honeycomb HgTe monolayer. Meanwhile, the strong interaction between HgTe and Al$_2$O$_3$(0001) ensures high stability of the atomic structure. Therefore, the TI states may be realized in HgTe/Al$_2$O$_3$(0001) at high temperature.