Colossal Shift Currents in Band-Inverted Bi Nanotubes Driven by the Interplay of Curvature and Spin-Orbit Coupling

The concept of non-trivial electronic structure combined with reduced dimensionality presents a promising strategy for advancing optical applications and energy harvesting technologies. Symmetry breaking in low dimensional system enables the emergence of non-linear optical responses, which are greatly amplified by the singular points of band inversion. Here, using first-principles calculations, the significant enhancement of the shift current in Bi nanotubes is investigated, driven by the combined effects of 1D geometry and non-trivial band order. By rolling a 2D Bi monolayer, which exhibits a quantum spin Hall phase, into a 1D nanotube, an extraordinarily large shift current of 4.94 A·Å² V⁻² is generated, two orders of magnitude larger than the experimental values in WS₂ nanotubes. The enhancement of the shift current in Bi nanotubes is demonstrated and attributed to the state mixing induced by the interplay of strong spin-orbit coupling, the curvature of the tube, and the non-trivial band order of Bi nanotubes. The robustness of this enhanced shift current against various perturbations is also discussed, such as oxidation and doping. The novel approach integrating non-trivial band order with reduced dimensionality sheds new light on advanced photovoltaic applications by harnessing both geometric advantages and exotic electronic structures for energy conversion.