Mid-infrared chirality and chiral thermal emission from twisted α-MoO3

Chirality in the mid-infrared spectral range plays a crucial role across physical, chemical, and biological sciences, yet sources of chiral infrared light are currently difficult to obtain. Their development, using principles from the mature field of metamaterials, requires complex three-dimensional architectures that call for high-resolution lithography. Here, we leverage the natural optical anisotropy found in several van der Waals crystals, for example α-MoO3, 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. Sources of chiral mid-infrared light are difficult to obtain. Here, the authors demonstrate that twisted bilayers of anisotropic α-MoO3 van der Waals crystals can emit mid-infrared thermal chiral radiation without any lithographic processes.