Rational design of quantum spin Hall phase in type-III van der Waals heterostructures

Van der Waals heterostructures (vdWHs) are effective platforms for exploring various attractive topological phases. Here, based on the lowenergy effective k center dot p model, we propose that the type-III vdWHs, which were previously considered as only belonging to trivial metallic phases, can realize the nontrivial quantum spin Hall (QSH) effect. We reveal that the band inversion of such a QSH phase is attributed to the band alignment of momentum space matching, i.e., the conduction band minimum and valence band maximum located at the same point in momentum space near the Fermi level. Moreover, using first-principles calculations, we show that the Mg(OH)(2)/Ga2O2 heterobilayer, a typical type-III vdWH with high thermodynamic stability, is an ideal candidate for achieving our strategy. We further calculate the helical gapless edge states and quantized spin Hall conductance, which are visible inside the global bandgap, thus facilitating the experimental observation. Our work offers a promising pathway for realizing the QSH phase in natural materials.