Tunable Optical Bistability Within the Bandgap in One-Dimensional Photonic Crystal Multilayer Structures Containing Weyl Semimetal.

In this paper, we propose a layered structure composed of Weyl semimetal (WSM) and one-dimensional photonic crystal (1D-PhC) to achieve low-threshold and tunable optical bistability (OB). By exploiting the bandgap characteristics of the photonic crystal and the strong third-order nonlinearity of WSM in the terahertz regime, reflective OB is realized within the photonic bandgap. It is shown that at certain frequencies inside the bandgap, the reflectance exhibits a jump with an increasing incident electric field, manifesting a clear hysteresis loop. The bistable threshold and hysteresis width can be effectively tailored by adjusting the Fermi energy and the thickness of the WSM layer. In addition, the influence of the incident angle and the parameters of the spacer layer on the OB threshold has also been elucidated. After parameter optimization, the incident electric field threshold is reduced to the order of 106 V/m. We believe that this structure can provide a reference for constructing optical bistable schemes with simple structures and low thresholds.