Rashba Effect in the Graphene/Ni(111) System

We report on angle-resolved photoemission studies of the electronic $\pi$ states of high-quality epitaxial graphene layers on a Ni(111) surface. In this system the electron binding energy of the $\pi$ states shows a strong dependence on the magnetization reversal of the Ni film. The observed extraordinarily large energy shift up to 225 meV of the graphene-derived $\pi$ band peak position for opposite magnetization directions is attributed to a manifestation of the Rashba interaction between spin-polarized electrons in the $\pi$ band and the large effective electric field at the graphene/Ni interface. Our findings show that an electron spin in the graphene layer can be manipulated in a controlled way and have important implications for graphene-based spintronic devices.

Figure 1

Geometry of the photoemission experiment on the graphene/Ni(111) system. Because of the fact that the three vectors ($\mathbf{E}$, $\mathbf{k}$, $\mathbf{s}$) are orthogonal to each other the Rashba effect can be observed in such a geometry.

Figure 2

High-quality graphene/Ni(111) system. (a) Constant current STM image of the graphene/Ni(111) surface ($+0.05\mathrm{V}$; 75 nA). The inset shows a LEED image obtained at 63 eV. (b) Constant current image showing atomic structure of the graphene monolayer ($-0.03\mathrm{V}$; 75 nA). Part of $\mathbf{b}$ is superimposed by the honeycomb lattice of graphene. (c) Angle-resolved photoemission spectra measured with $h\nu =40.8\mathrm{eV}$ along $\overline{\Gamma }-\overline{M}$ direction of the surface Brillouin zone. Ni $3d$ as well as $\pi$ and $\sigma$ states of graphene layer are marked in the figure.

Figure 3

Manifestation of the Rashba effect in the graphene layer on Ni(111). (a) Series of representative photoelectron spectra of the graphene/Ni(111) system for two different emission angles (marked in the plot) and two directions of magnetization, respectively, (according to Fig. 1). A clear energy shift of the $\pi$ states is visible for spectra taken at $\theta =24°$. (b) Energy dispersions extracted from the photoemission spectra measured for two opposite directions of magnetization. (c) Rashba splitting $\Delta E(\mathbf{k})$ obtained from the data shown in (b) as a function of the wave vector $k$ along the $\overline{\Gamma }-\overline{M}$ direction of the surface Brillouin zone.