Exciton Effect On Shift Current In Single-Walled Boron-Nitride Nanotubes

In the present paper, we investigate the exciton effect on the shift current in single-walled boron-nitride nanotubes using effective mass theory combined with the Bethe-Salpeter equation to include the exciton effect. We found that the shift current is enhanced by the exciton effect compared to that of free electron-hole pairs and that the direction of the shift current is determined by the chiral index of the nanotube even in the presence of excitons. We provide a simple explanation of why the chiral index determines the direction of the shift current from a bond structure viewpoint via the Rice-Mele model.