Prediction of High Chern Number and Bulk Photovoltaic Current in Janus 1T′ Transition Metal Dichalcogenides under Circularly Polarized Light

Light-induced topological phase transition and electric current generation have been receiving tremendous attention recently. In the current work, first-principles calculations are used to investigate an experimentally fabricated material family, 1T′ Janus transition metal dichalcogenide monolayers. It is shown that under time-periodic light field pump, these materials could exhibit twice of topological phase transition, yielding quantum anomalous Hall states with Chern number of ±2 under an intermediate light intensity. Furthermore, such a pump light could simultaneously generate a static direct current that flows in the plane. Under such a transient phase transition, the dielectric function shows contrasting behaviors. It is also suggested that such topological phase transitions can be detected using a weak probe light to generate bulk photovoltaic effect. This is a second-order nonlinear optical response, and both intrinsic shift current and extrinsic injection current would emerge, which can be separated depending on their flow direction. With these theoretical and computational results, an all-optical strategy to control and detect the ultrafast quantum anomalous Hall transitions is predicted.