Anomalous Suppression of Higher-Order Nonlinearities in 3D Dirac Semimetals

Three dimensional Dirac semimetals are often thought to share the same essential physics as 2D Dirac materials. Here, we present a counter-intuitive feature of 3D Dirac semimetals that sets them apart from their 2D counterparts: the absence of intraband nonlinearities beyond the third order at near-zero temperatures at or close to a critical field strength. Using complementary analytical theory and rigorous, nonperturbative time-domain simulations, we show that this effect is robust against changes in incident field polarization and remains significant even at finite temperatures. Additionally, we identify regimes where 3D Dirac semimetals effectively function as bulk versions of 2D Dirac semimetals with the potential for superior performance in terms of high-harmonic generation. Our work fills a vital gap in understanding the nonlinear terahertz response of Dirac electrons, and paves the way for the development of chip-integrable, nanophotonic devices and optoelectronics based on Dirac materials.