Temporal Twistronics

The concept of twistronics and moiré physics, which is present in twisted two-dimensional bilayer materials, has recently attracted growing attention in various fields of science and engineering such as condensed matter physics, nanophotonics, polaritonics and excitonics. The twist angle between the two layers has offered an additional degree of control over electron and photon interaction with such structures. Inspired by the photonic version of twistronics, here we introduce and investigate theoretically the temporal analogue of twistronics in anisotropic optical media. We study how a monochromatic electromagnetic plane wave propagating in a spatially unbounded, anisotropic medium undergoes major changes when the relative permittivity tensor of the medium is rapidly changed in time to create a new anisotropic medium that is the rotated version of the original medium. We consider both the elliptic and hyperbolic anisotropic scenarios. The propagation-angle-dependent forward (FW) and backward (BW) waves with their converted frequencies and relative amplitudes are obtained. To concentrate on the main features of this concept without getting into details of dispersion, in our work here we assume dispersionless and lossless material parameters. Our results reveal how frequency conversion is highly dependent on the direction of propagation of the original wave, rotation angle, and initial values of the material parameters, proposing another class of "magic angles" for such temporal twistronics.