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

Abstract

van der Waals heterostructures made from graphene and three-dimensional topological insulators promise very high electron mobilities, a nontrivial spin texture, and a gate-tunability of electronic properties. Such a combination of advantageous electronic characteristics can only be achieved through proximity effects in heterostructures, as graphene lacks a large enough spin–orbit interaction. In turn, the heterostructures are promising candidates for all-electrical control of proximity-induced spin phenomena. Here, we explore epitaxially grown interfaces between graphene and the lattice-matched topological insulator Bi2Te2Se. For this heterostructure, spin–orbit coupling proximity has been predicted to impart an anisotropic and electronically tunable spin texture. Polarization-resolved second-harmonic generation, Raman spectroscopy, and time-resolved magneto-optic Kerr microscopy are combined to demonstrate that the atomic interfaces align in a commensurate symmetry with characteristic interlayer vibrations. By polarization-resolved photocurrent measurements, we find a circular photogalvanic effect which is drastically enhanced at the Dirac point of the proximitized graphene. We attribute the peculiar gate-tunability to the proximity-induced interfacial spin structure, which could be exploited for, e.g., spin filters.

Twist-angle dependent proximity induced spin-orbit coupling in graphene/transition metal dichalcogenide heterostructures

“…Using thin layers of three-dimensional (3D) topological insulators (TIs) like Bi 2 Te 3 or Bi 2 Se 3 can introduce even larger SOC [31,32]. In experiment, such graphene/TI heterostructures can be fabricated using either exfoliation techniques [33][34][35][36][37] or techniques like chemical vapor deposition (CVD) [38][39][40][41]. While the former case should result in incommensurate structures with * thomas.naimer@physik.uni-regensburg.de random twist angle, the latter will produce commensurate structures with mostly fixed twist angle Θ (Θ = 0°o r Θ = 30°) [38,40] between the two layers.…”

“…In experiment, such graphene/TI heterostructures can be fabricated using either exfoliation techniques [33][34][35][36][37] or techniques like chemical vapor deposition (CVD) [38][39][40][41]. While the former case should result in incommensurate structures with * thomas.naimer@physik.uni-regensburg.de random twist angle, the latter will produce commensurate structures with mostly fixed twist angle Θ (Θ = 0°o r Θ = 30°) [38,40] between the two layers. Similar to graphene/TMDC heterostructures, the twist angle in graphene/TI heterostructures will also play a significant role for the proximity SOC that graphene obtains.…”

Twist-angle dependent proximity induced spin-orbit coupling in graphene/topological insulator heterostructures

“…Using thin layers of three-dimensional topological insulators (TIs) like Bi 2 Te 3 or Bi 2 Se 3 can introduce even larger SOC [31,32]. In experiment, such graphene/TI heterostructures can be fabricated using either exfoliation techniques [33][34][35][36][37] or techniques like chemical vapor deposition (CVD) [38][39][40][41]. While the former case should result in incommensurate * thomas.naimer@physik.uni-regensburg.de structures with random twist angle, the latter will produce commensurate structures with mostly fixed twist angle ( = 0 • or 30 • ) [38,40] between the two layers.…”

“…In experiment, such graphene/TI heterostructures can be fabricated using either exfoliation techniques [33][34][35][36][37] or techniques like chemical vapor deposition (CVD) [38][39][40][41]. While the former case should result in incommensurate * thomas.naimer@physik.uni-regensburg.de structures with random twist angle, the latter will produce commensurate structures with mostly fixed twist angle ( = 0 • or 30 • ) [38,40] between the two layers. Similar to graphene/TMDC heterostructures, the twist angle in graphene/TI heterostructures will also play a significant role for the proximity SOC that graphene obtains.…”