Temporal Brewster anomaly and collimated wave steering in Dirac materials

Abstract: Temporal disorder-random temporal fluctuations of material parameters-has recently emerged as an effective tool for controlling wave propagation, analogous to Anderson localization in spatially disordered systems. Here, we theoretically introduce and analyze the temporal Brewster anomaly in pseudospin-1/2 Dirac systems, demonstrating that Dirac waves remain delocalized along a vector potential with fixed direction despite random temporal variations in its magnitude. In contrast, waves propagating at any off-axis angle exhibit pronounced spatial localization and diffusive behavior. This directional selectivity arises from temporal impedance matching, previously identified as the mechanism suppressing temporal reflection along the vector potential axis. By analyzing temporal reflectance, wave group velocity, and pulse propagation, we establish that these systems function as dynamic directional filters, achieving collimated wave steering purely through temporal modulation. In Dirac materials, external electric fields or mechanical strain can dynamically control the orientation and strength of the vector potential modulation, enabling precise, real-time tuning of directional wave transmission. The temporal Brewster anomaly thus offers a robust and versatile approach for adaptive wave steering, promising significant technological applications in electronic and photonic devices.