Proximity Spin Interactions in 2D Materials and Correlated Phases

Graphene has weak spin-orbit coupling and no magnetic order. But when placed in contact with a strong spin-orbit coupling material, such as a TMDC, or a ferromagnet, such as Cr2Ge2Te6, Dirac electrons acquire strong spin-orbit or exchange coupling, respectively. Such proximity effects render graphene suitable for spintronic applications that require spin manipulation [1]. In addition, graphene with strong proximity spin interactions can host novel topological states [2]. Fascinating new phenomena appear when bilayer graphene gets encapsulated by a TMDC from one side, and a ferromagnet from another. The resulting, so called ex-so-tic structure [3], offers spin swap functionality: switching spin-orbit and exchange coupling on demand by the gate. In this talk, I will review the recent developments in the proximity phenomena in graphene, and present some recent theoretical results on the control of the proximity spin-orbit and exchange coupling by twisting the van der Waals layers. I will show that the signature proximity spin-orbit coupling in graphene---valley Zeeman coupling---can be efficiently tuned by the twist angle [4], and that proximity exchange coupling can be switched by the twist angle, and even morph from ferromagnetic to antiferromagnetic [5]. Finally, I will also discuss the emergence of new correlated phases in AB bilayer and ABC trilayer graphene [6] due to the presence of proximity spin-orbit and exchange couplings. Support from DFG SPP1244, SFB 1277, FLAGERA 2DSOTECH, and EU 2DSPINTECH is acknowledged.<br/>[1] J. Sierra et al, Nature Nanotechnology, 16, 856 (2021)<br/>[2] P. Högl et al, Phys. Rev. Lett. 124, 136403 (2020)<br/>[3] K. Zollner et al, Phys. Rev. Lett. 125, 196402 (2020)<br/>[4] T. Naimer et al, Phys. Rev. B 104, 195156 (2021)<br/>[5] K. Zollner and J. Fabian, Phys. Rev. Lett. 128, 106401 (2022)<br/>[6] Y. Zhumagulov et al, arXiv: arXiv:2305.14277, 2307.16025