A PbS monolayer is demonstrated to be a novel platform for topological, valleytronic, and optical phenomena. Compressive strain can turn the trivial monolayer into a topological insulator. Optical pumping can facilitate charge, spin, and valley Hall effects tunable by external strain and light ellipticity. Similar results apply to other IV–VI semiconductors.
Figure 1 Strain-induced topological phases in the PbS (001) monolayer. a) The band gaps (Eg) and the phase diagrams as functions of the biaxial strain (ε), calculated by HSE+SOC and PBE+SOC methods. b) The band gaps at X and Y points (mX, Y), the fundamental gap (mF) across the entire 2D BZ, and the phase diagram as functions of the uniaxial strain (εy), calculated by the HSE+SOC method.
Figure 2 The optical spin-valley polarizations and the anomalous Hall effects for the excited electrons in optoelectronic transport.