Strong chirality and asymmetric transmission effect in twisted bilayer α-MoO3 in terahertz band

Chirality and asymmetric transmission have wide-ranging applications in fields such as optics, chemical synthesis, pharmaceutical research, biological analysis, materials science and communication technology. In this work, we have demonstrated a terahertz (THz) device with strong chirality and asymmetric transmission effect based on a twisted bilayer α-MoO3. The unique optical response can be realized by adjusting structural parameters such as the thicknesses of the layers as well as the angle of relative rotation. It is found that the proposed structure achieves a giant circular dichroism (CD) value of 0.81 at 9.8 THz, which originates from the symmetry breaking of the structure. The phenomenon has been approved by the polarization conversion and the distributions of the electric field. In addition, the device exhibits the asymmetric transmission effect for circularly polarized wave incidence. The results show that the forward and backward transmissivity of circularly polarized waves with different handedness exhibit a significant difference of up to 0.55 at 9.2 THz. This work simultaneously achieves chirality and asymmetric transmission effect in the terahertz band, which paves the way for developing terahertz devices capable of chirality manipulation and optical isolation.