Weyl semimetal/dielectric/Weyl semimetal stack for highly circularly polarized thermal radiation.

Abstract

Highly circularly polarized (CP) infrared thermal radiation is greatly in demand because of its significant potential in mid-infrared (mid-IR) applications. To exploit the magnitude and quality factor of circular dichroism (CD) simultaneously, a lithography-free platform consisting of a Weyl semimetal (WSM)/dielectric (Ge)/WSM stack sitting on a metallic substrate (Mo) is proposed. A chiral response and varying CD values from -1 to 0.957 have been demonstrated. The numerical results from a generalized 4 × 4 transfer matrix algorithm verify that the chiral structure manifests a remarkably high quality factor (Q-factor) of 605. The effect of the thickness of each layer in the stack on the CD value is investigated. Moreover, it is identified that the design results in an angle-independent performance. A dual-channel chiral absorber operating in the 18-21 μm wavelength range has also been achieved. Our simple yet powerful paradigm could offer a new way of manipulating the Q-factor and resonance wavelength of a chiral absorber while maintaining near-unity CD, offering a new approach for the advancement of more efficient and tunable chiral optical devices. The approach is generally applicable to other planar configurations with different WSMs and can be extended to other wavelengths.