The photogalvanic effect induced by quantum spin Hall edge states from first-principles calculations

Based on non-equilibrium Green's function combined with density functional theory (NEGF-DFT), we theoretically investigate the spin-related photogalvanic effect (PGE) in topological insulators BiBr and SbBr nanoribbons from atomic first-principles calculations. It is demonstrated that the PGE generated photocurrents by quantum spin Hall edge states (QSHES) are in general pure spin currents due to the presence of time reversal and mirror symmetries, which is independent of the photon energies, polarization, and incident angles. Although the QSHES are topologically protected and robust against defects and impurities during their transport, the spin photocurrent generated by these edge states via the PGE is particularly sensitive to defects. By tuning the defect position of the nanoribbons, the magnitude of spin related photocurrent generated by the PGE can be significantly increased compared with that in pristine nanoribbons. Our work not only reveals the defect effect of PGE but also demonstrates the great potential of defect engineered topological insulator nanoribbons for novel application in two-dimensional opto-spintronic devices.