Tunable Terahertz Optical Bistability Enabled by Synergistic Topological Edge States and Weyl Semimetal.

Low-threshold optical bistability (OB) holds significant application prospects in various fields. In this work, we theoretically propose a one-dimensional photonic crystal heterostructure incorporating a Weyl semimetal (WSM) layer. The design synergistically combines the local field enhancement associated with topological edge states (TESs) and the strong intrinsic nonlinearity of WSM. Through parameter optimization, a tunable OB phenomenon with a threshold of 105 V/m for both the incident electric field and the transmitted electric field is achieved in the terahertz regime. Furthermore, key characteristics of the OB, including the switching threshold and hysteresis loop width, can be flexibly manipulated by adjusting parameters such as the angle of incidence, the incident wavelength, and the thickness of the WSM layer. We believe that the proposed scheme may provide useful theoretical guidance for future studies of low-threshold nonlinear phenomena and terahertz photonic functionalities based on WSM.