All-Optically Controlled Topological Current Switcher Based on Silicene-Like Nanoribbons

Low-dimensional topological insulator materials, such as silicene-like 2-D materials, have wide applications in electronic, spintronic, and optoelectronic nanodevice, by utilizing their topologically protected edge states. In theoretical studies, Floquet theorem is usually employed in the nanosystems under light irradiation with high-frequency approximation, which may not be accessible in experimental research. In this work, we study the quasienergy spectra and edge-state transport of silicene-like nanoribbons under low-frequency light irradiation (in visible wavelengths), by extracting the zero-photon component from the nonperturbative Floquet bands. These silicene-like nanoribbons undergo topological phase transition from quantum spin Hall (QSH) to quantum anomalous Hall (QAH) insulator under circularly polarized light, accompanied by helical edge modes to chiral ones. The propagation direction of edge-mode current in QAH nanoribbons can be switched by left-/right-circularly polarized (LCP/RCP) light, and such a current-switching effect is then confirmed in heterojunction composed of QSH and QAH nanoribbons. Based on the all-optically controlled current-switching effect, we design a three-terminal current switcher, with one input terminal, two output ones, and central device irradiated by LCP/RCP light. Conductance and real-space local current distribution of the proposed nanosystem reveal that the input current can indeed be switched into specific output terminal by LCP/RCP light. The proposed current switcher changes the electron movement very quickly, and we believe that it would have potential applications in high-speed photoelectric nanodevices.