Spin-charge Conversion in Ferromagnetic Metal Fe / Topological Dirac Semimetal α-Sn Heterostructures

Topological surface states (TSS) of topological materials are promising for effective spin-charge interconversion. However, when interfacing a topological material with a ferromagnetic layer, the TSS is destroyed by time-reversal symmetry breaking, and inserting a conductive spacer layer is usually required to preserve TSS [1, 2]. However, this method could cause current shunting and increase the probability of spin scattering at the interface. In this work, we demonstrate that highly efficient spin-charge conversion (SCC) is possible when directly interfacing topological Dirac semimetal (TDS) α-Sn [3] with ferromagnetic Fe.

Spin-pumping experiments was carried out at room temperature on ferromagnetic Fe / TDS α-Sn heterostructures with varying the α-Sn thickness. We observed clear SCC, indicated by the simultaneous observation of ferromagnetic resonance (FMR) and a voltage peak that is proportionate to the applied microwave power at FMR conditions in the samples with Sn thickness above 25 nm. The inverse Edelstein length is estimated to be ~1.2 nm, which is comparable to the largest value reported thus far at room temperature [2]. Combined with DFT calculations, our results indicate that the SCC occurs at the TSS of TDS on the substrate side, suggesting the long spin-diffusion length of TDS α-Sn.

[1] Noel, P. et al. Phys. Rev. Lett. 120, 167201 (2018).

[2] J.-C. Rojas-Sánchez et al., Phys. Rev. Lett. 116, 096602 (2016).

[3] L. D. Anh et al., Adv. Mater. 33, 2104645 (2021).