|
We study graphene nanoribbons in the presence of spatially varying magnetic fields produced e.g. by nanomagnets [1]. We show both analytically and numerically that an exceptionally large Rashba spin orbit interaction (SOI) of the order of 10 meV can be produced by the non-uniform magnetic field. As a consequence, helical modes, conducting modes which transport opposite spins in opposite directions [1-5], exist in armchair nanoribbons that exhibit nearly perfect spin polarization and are robust against boundary defects. This paves the way to realizing spin filter devices in graphene nanoribbons in the temperature regime of a few Kelvins. They find applications also in Cooper pair splitters. If a nanoribbon in the helical regime is in proximity contact to an s-wave superconductor, the nanoribbon can be tuned into a topological phase sustaining Majorana fermions. Helical modes can be also generated in other two-dimensional systems such as MOS2 [5]. Moreover, in our previous work we have demonstrated that helical modes exist also in other carbon-based materials: carbon nanotubes [2,3] and bilayer graphene [4], where intrinsic spin orbit interaction is enhanced due to curvature effects.
[1] J. Klinovaja and D. Loss, Phys. Rev. X 3, 011008 (2013). [2] J. Klinovaja, M. J. Schmidt, B. Braunecker, and D. Loss, Phys. Rev. Lett. 106, 156809 (2011). [3] J. Klinovaja, S. Gangadharaiah, and D. Loss, Phys. Rev. Lett. 108, 196804 (2012). [4] J. Klinovaja, G. J. Ferreira, and D. Loss, Phys. Rev. B 86, 235416 (2012). [5] J. Klinovaja and D. Loss, arXiv:1304.4542. |
|