Proximity Effect Induced Electronic Properties of Epitaxial Graphene on Bi2Te2Se

TL;DR

This study demonstrates how interfacing graphene with a topological insulator (Bi2Te2Se) induces a significant spin-orbit gap and a phase transition, enabling spin-polarization of graphene's π-electrons for potential spintronics applications.

Contribution

The paper reports the experimental growth of graphene/Bi2Te2Se heterostructures and shows how the proximity effect induces a sizable spin-orbit gap and a quantum spin Hall phase in graphene.

Findings

Spin-orbit gap of ~20 meV induced in graphene

Tunable Dirac point separation via Cs adsorption

Observation of phase transition to quantum spin Hall state

Abstract

We report that the {\pi}-electrons of graphene can be spin-polarized to create a phase with a significant spin-orbit gap at the Dirac point (DP) using a graphene-interfaced topological insulator hybrid material. We have grown epitaxial Bi2Te2Se (BTS) films on a chemical vapor deposition (CVD) graphene. We observe two linear surface bands both from the CVD graphene notably flattened and BTS coexisting with their DPs separated by 0.53 eV in the photoemission data measured with synchrotron photons. We further demonstrate that the separation between the two DPs, {\Delta}D-D, can be artificially fine-tuned by adjusting the amount of Cs atoms adsorbed on the graphene to a value as small as {\Delta}D-D = 0.12 eV to find any proximity effect induced by the DPs. Our density functional theory calculation shows a spin-orbit gap of ~20 meV in the {\pi}-band enhanced by three orders of magnitude from that of a pristine graphene, and a concomitant phase transition from a semi-metallic to a quantum spin Hall phase when {\Delta}D-D $\leq$ 0.20 eV. We thus present a practical means of spin-polarizing the {\pi}-band of graphene, which can be pivotal to advance the graphene-based spintronics.