Ultrafast All‐Optical Terahertz Switchable Modulation Using Van Der Waals Fe 4 GeTe 2 /Bi 2 Te 3 Heterostructures

Abstract 2D all‐van der Waals Fe n GeTe 2 /topological insulator heterostructures present compelling prospects for the development of advanced opto‐spintronic devices, attributed to the coupling between ferromagnetic and topological characteristics. The ultrafast laser‐induced terahertz (THz) switchable modulations in Fe 4 GeTe 2 /Bi 2 Te 3 heterostructures are investigated by employing optical pump‐THz probe (OPTP) spectroscopy. By comparing the OPTP results of Fe 4 GeTe 2 /Bi 2 Te 3 with those obtained from single Fe 4 GeTe 2 and Bi 2 Te 3 films, it is found that the optically‐induced THz modulation is attributed to both interface carrier accumulation and thermal effect in Fe 4 GeTe 2 . Furthermore, the thickness‐ and temperature‐dependent measurements enable the establish comprehensive rules governing the switching of photoconductivity from positive to negative. The findings highlight a promising pathway for optically controlled THz modulators, achieved by modulating charge dynamics at temperatures near the topological‐to‐trivial transition in all‐van der Waals ferromagnetic Fe 4 GeTe 2 /topological insulator heterostructures.