  A novel topological insulator with tunable edge states, called quantum
spin-quantum anomalous Hall (QSQAH) insulator, is predicted in a
heterostructure of a hydrogenated Sb (SbH) monolayer on a LaFeO3 substrate by
using ab initio methods. The substrate induces a drastic staggered exchange
field in the SbH film, which plays an important role to generate the QSQAH
effect. A topologically nontrivial band gap (up to 35 meV) is opened by Rashba
spin-orbit coupling, which can be enlarged by strain and electric field. To
understand the underlying physical mechanism of the QSQAH effect, a
tight-binding model based on px and py orbitals is constructed. With the model,
the exotic behaviors of the edge states in the heterostructure are
investigated. Dissipationless chiral charge edge states related to one valley
are found to emerge along the both sides of the sample, while low-dissipation
spin edge states related to the other valley flow only along one side of the
sample. These edge states can be tuned flexibly by polarization-sensitive
photoluminescence controls and/or chemical edge modifications. Such flexible
manipulations of the charge, spin, and valley degrees of freedom provide a
promising route towards applications in electronics, spintronics, and
valleytronics.
