Gate-Tunable Helical Currents in Commensurate Topological Insulator/Graphene Heterostructures

Interfaces between graphene and the topological insulator Bi₂Te₂Se feature a lattice-matched, commensurate stacking, where proximity effects have been predicted to impart an anisotropic and electronically tunable spin texture [1]. Here, we demonstrate the growth of such expitaxial and commensurate interfaces, we characterize their interfacial symmetries by optical spectroscopies, and we adress the gate-tunable spin-orbit poximity by polarization resolved photocurrent spectroscopy. As a main finding, we demonstrate a circular photogalvanic effect which is drastically enhanced at the Dirac point of the proximitized graphene. We attribute the gate-tunability to the proximity-induced interfacial spin structure, which could be exploited, for example, in spin filters [2].

[1] Song et al. Nano Lett. 18, 2033 (2018)

[2] Kiemle et al. ACS Nano 16, 12338 (2022).