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

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 Fe₄GeTe₂ films and Bi₂Te₃/Fe₄GeTe₂ ferromagnetic/topological heterostructures. Our results show that these heterostructures exhibit effective THz electromagnetic shielding. The complex conductivity spectra of Fe₄GeTe₂ films and Bi₂Te₃/Fe₄GeTe₂ heterostructures with varying Fe₄GeTe₂ thicknesses are analyzed using the Drude–Smith model. We quantitatively examine how Fe₄GeTe₂ layer thickness affects the direct current conductivity, plasma frequency, carrier momentum scattering time, and back-scattering coefficient. As the number of Fe₄GeTe₂ layers increases, intra-layer back-scattering events for charge carriers become more frequent. This work provides THz frequency spectra for both Fe₄GeTe₂ and Bi₂Te₃/Fe₄GeTe₂, aiding in the design and optimization of THz modulators and detectors.