Enhanced terahertz emission by efficient spin-to-charge conversion in (Bi1−xSbx)2Te3 based heterostructures

Abstract

The enhanced terahertz (THz) emission in the spintronics based emitter is of extreme significance for the realization of THz probing and imaging. The THz emitter based on three-dimensional topological insulators (TIs), (Bi1–xSbx)2Te3 (BST) with spin-momentum-locked Dirac surface states, is expected to exhibit strong THz emission efficiency due to the high spin-to-charge current conversion efficiency. In this study, by tuning the Fermi level close to the Dirac point through adjusting the Sb composition to 0.95, (Bi0.05Sb0.95)2Te3/Co exhibits more pronounced THz pulse emission due to the unique topological surface states. The THz emission could be further enhanced by optimizing the thickness of the BST and Co layers. In addition, by inserting an Au layer between Co and BST, a Rashba-mediated Dirac surface state is formed due to the interaction between the Au film and the topological surface states of BST, which significantly enhances the emission efficiency—reaching 127% of the original signal when the Au thickness is 2 nm. Furthermore, in the BST/Co/Ta heterostructure, THz emission is further boosted due to the combined contributions of the inverse Rashba–Edelstein effect and the inverse spin Hall effect, achieving an intensity of 143% of that in the BST/Co heterostructure. These findings highlight the potential of TI-based heterostructures as high-performance, room-temperature THz sources, with broad applications in ultrafast spectroscopy, imaging, and next-generation communication technologies.