Mid-IR chirality and chiral thermal emission through twisting

Abstract: Chirality in the mid-infrared spectral range plays a crucial role across physical, chemical, and biological sciences, yet sources of chiral infrared light do not currently exist. Their development, using principles from the mature field of metamaterials, requires complex three-dimensional architectures that call for high-resolution lithography. We leverage the natural optical anisotropy found in several van der Waals crystals, for example $\alpha$-MoO$_3$, to demonstrate experimentally that its twisted bilayers break inversion-rotation symmetry and are thereby intrinsically chiral. Via direct thermal emission measurements of microscopic twisted bilayers, we demonstrate that these heterostructures generate chiral light through incandescence. Twisted configurations of van der Waals materials do not require any lithography, and offer a platform for large-scale chiral filters and thermal sources beyond conventional meta-architectures.