Ultrafast electron transport in 2D van der Waals heterostructures Bi₂Te₃/Fe₄GeTe₂ probed by terahertz spectroscopy

Abstract The research on two-dimensional (2D) magnetic materials and their heterostructures is crucial in fields like spintronics, materials science, and condensed matter physics. This study uses terahertz (THz) time-domain spectroscopy to investigate ultrafast electron transport properties in both van der Waals Fe 4 GeTe 2 films and Bi 2 Te 3 /Fe 4 GeTe 2 ferromagnetic/topological heterostructures. Our results show that these heterostructures exhibit effective THz electromagnetic shielding. The complex conductivity spectra of Fe 4 GeTe 2 films and Bi 2 Te 3 /Fe 4 GeTe 2 heterostructures with varying Fe 4 GeTe 2 thicknesses are analyzed using the Drude–Smith model. We quantitatively examine how Fe 4 GeTe 2 layer thickness affects the direct current conductivity, plasma frequency, carrier momentum scattering time, and back-scattering coefficient. As the number of Fe 4 GeTe 2 layers increases, intra-layer back-scattering events for charge carriers become more frequent. This work provides THz frequency spectra for both Fe 4 GeTe 2 and Bi 2 Te 3 /Fe 4 GeTe 2 , aiding in the design and optimization of THz modulators and detectors.