Proximity physics in graphene: spin-orbit coupling, exchange, field effects, and pseudohelical states*

Graphene and novel 2d materials offer new perspectives for spintronics [1]. Since graphene itself has no band gap, its spintronic applications will be limited as a highly efficient spin transfer channel. Instead, heterostructures of graphene and two-dimensional transition-metal dichalcogenides (TMDC) are emerging as systems in which both orbital and spin properties can be controlled by gating, thus offering a materials basis for spintronic applications, such as optospintronics [2]. But these van der Waals stacks also yield interesting fundamental physics. For example, graphene on WSe2 exhibits giant spin anisotropy, and is predicted to support protected pseudohelical states in flakes [4], with a bulk spin-orbit gap of about 1 meV. Even more fascinating is bilayer graphene on TMDCs, as the spin properties of this material can be controlled (turned ON and OFF) by gate voltage, creating a platform for spin-orbit valves and spin transistors [5]. Finally, I will also talk about magnetic proximity effects in graphene on ferromagnetic insulators. Here too bilayer graphene is predicted to yield field-effect
magnetism (exchange splitting) [6], which opens a potential for a whole new class of phenomena and device concepts.

[1] W. Han, R. Kawakami, M. Gmitra, and J. Fabian, Nature Nanotechnology 9, 794 (2014)
[2] M. Gmitra and J. Fabian, Phys. Rev. B 92, 155403 (2015)
[3] A. Cummings, J. Garcia, J. Fabian, and S. Roche,
[4] M. Gmitra, D. Kochan, and J. Fabian, Phys. Rev. B 93, 155104 (2016); T. Frank, P. Högl, M. Gmitra, D. Kochan, and J. Fabian, arxiv.1707.02124
[5] M. Gmitra and J. Fabian, Phys. Rev. Let. 119, 146401 (2017)
[6] 6. K. Zollner, M. Gmitra, and J. Fabian, arXiv:1710.08117