Unraveling the Role of Au and Al Interlayers in Observing Spin-Charge Conversion in Sb₂Te₃ Topological Insulator

Topological insulators (TIs) can be used to control the magnetization of ferromagnetic (FM) layers in TI/FM heterostructures through spin-charge conversion (SCC) mechanisms driven by the topological surface state (TSS).¹ Non-magnetic interlayers at the TI/FM interface are frequently employed to enhance SCC efficiency, as demonstrated in Sb₂Te₃/Au/Co(Fe) heterostructures.^2,3 However, the effect of Au on the TSS of Sb₂Te₃ was not fully characterized.
Here, we study the different impact of Al and Au interlayers at the interface of Sb₂Te₃/Co heterostructures. Spin pumping experiments show that SCC is not observed in the presence of Al, in net contrast to the use of Au.^2,3 To understand the origin of this behavior, in-situ X-ray Photoemission Spectroscopy and Angle-Resolved Photoemission Spectroscopy measurements with synchrotron radiation were conducted during the deposition of Al and Au thin films on the Sb₂Te₃ surface. The analysis reveals the highly reactive character of Al and the disappearance of TSS upon deposition of only 1 nm thick Al film, at variance with the case of Au, which preserves the TSS.
These findings highlight the critical choice of non-magnetic material interlayers in devices for SCC applications and underscore the importance of preserving the TSS for efficient device performance.

Bibliography
1. Hirohata, A. et al. Review on spintronics: Principles and device applications. J Magn Magn Mater 509, 166711 (2020).
2. Longo, E. et al. Spin-Charge Conversion in Fe/Au/Sb 2 Te 3 Heterostructures as Probed By Spin Pumping Ferromagnetic Resonance. Adv Mater Interfaces 2101244, 2101244 (2021).
3. Longo, E. et al. Large Spin-to-Charge Conversion at Room Temperature in Extended Epitaxial Sb2Te3 Topological Insulator Chemically Grown on Silicon. Adv Funct Mater 2109361, (2021).