Numerical model for the complete THz spintronic emission process

Spintronic terahertz emitters (STEs) are becoming increasingly popular for their potential applications in a wide arena of domains from 6G wireless communications to biomedical diagnostics. In spite of the experimental progress a full theoretical/numerical model of the ultrafast spin dynamics that generates the broadbad THz radiation, remains elusive. The inherent far-from-equilibrium dynamics from mulitple simultaneous quasi-particle interactions presents an intricate many-body quantum phenomena, which hitherto has been only modeled with phenomenological equations that present a far-from-detailed picture of the actual dynamics. Here we develop a comprehensive model which integrates the spin current generation in the ferromagnet and spin-to-charge conversion in the rashba spin-orbit split bands of the heavy metal. The temporal evolution of the charge current in the heavy metal is further converted to the emitted THz radiation using a transfer matrix formulation to complete the full STE model. Using this model we investigate the role of rashba parameter in altering the emitted Thz radiation. Our model elucidates, for the first time, the inherent ultrafast spin dynamics in STEs and higlights design principles for optimizing the Thz emission bandwidth.