Intrinsic Switchable Valley-Polarized Photocurrent in -InSe

Valleytronics, focusing on the charge carriers occupying valleys (local energy extrema) of the energy bands in semiconductors, demonstrates an additional degree of freedom besides the spin and charge. Usually, the inequivalent valley "states" in transition metal disulfides (TMDs) could be manipulated by external magnetic fields by controlling the valley-polarized carriers in spin-coupled valleys. Here, we found that the valley polarization of the photocurrent in epsilon-InSe could be intrinsically manipulated without the external field by the all-optical contactless method. The transient circular photogalvanic effect (CPGE)-induced photocurrent revealed by terahertz emission could be reversed only by selected pumping carriers from vertically split valence bands into different Rashba valleys. The switchable Rashba valley polarization, i.e., the optical orienting valley degree of freedom, could be fulfilled by the synergetic effects between the momentum-dependent Zeeman-like field due to the emergent nonzero Berry curvature and the Rashba splitting. Our results suggest that the spontaneous symmetry breaking could degenerate the given valley in epsilon-InSe and give a new roadmap for the manipulation of the valley degree of freedom intrinsically.