Optical control of charge carrier behavior and electron-phonon strong coupling in heterostructures
Phys. Rev. B 113, 035419 – Published 14 January, 2026
DOI: https://doi.org/10.1103/xykr-mqm5
Abstract
The combination of ferromagnetic metals and nonmagnetic light metals, exemplified by the bilayer heterostructures, has emerged as an outstanding platform for achieving terahertz (THz) emission based on both spin-to-charge and orbital-to-charge current conversion. Although some of many-body phenomena based on the interactions among charge, spin, orbital, and lattice degrees of freedom in such heterostructures have been investigated by using THz emission spectroscopy recently, other many-body effects affecting the THz absorption properties of these bilayer systems still remain relatively unexplored. Here we characterize the THz transmission/absorption properties of (CFB)/Ti heterostructures and investigate the many-body interactions associated with photons, charge carriers, and phonons in them. It is demonstrated that the heterostructures exhibit metallic-type charge carrier behavior in the range of 0.1–1.2 THz, whereas a significant Fano asymmetric line shape is observed in the regime of 1.2–2 THz. The Fano resonance can be attributed to the strong coupling between free electrons and interface phonons. More importantly, we show that this coupling can be modulated by pumping/exciting the heterostructures with a continuous-wave laser. Specifically, the CFB(15 nm)/Ti sample exhibits a large modulation depth of approximately 82.5% at 1.65 THz under a power density of . Furthermore, by fitting the experimental data with the Drude-Fano model, we also obtain the characteristic parameters of the charge carriers and electron-phonon coupling, as well as their dependencies upon the pump power density and CFB thickness. These findings not only offer a deeper understanding of the many-body THz response in CFB/Ti systems and their active control but also advance the research on CFB-based THz devices.
