Spin Dependent Scattering in Graphene Systems: From Impurity Characterization to Birefringent Electron Optics

An important effect on the dynamics of spins in materials is the spin-orbit interaction (SOI), which reflects/arises from intrinsic lack of inversion symmetry in the lattice structure, or via broken symmetries in the system due to external or interfacial fields (Rashba interaction). Although intrinsic SOI is weak in graphene, the Rashba SOI can in fact be large due to strong local hybridizations by impurities of defects or by manipulation of substrates or applied gates [1]. Indeed, resonant scatterers, limiting electron mobility in graphene, appear likely due to impurities such as hydrogen or other adsorbed atoms, molecules, clusters of impurities or vacancies, or can be controllably implemented by metallic islands deposited on (or grown under) graphene. We have studied electron/hole transport in graphene under sizeable SOI and address theoretically some of the anticipated observables due to this effect. Moreover, we show that Rashba SOI in graphene gives rise to optical birefringence in electron optics, which in essence reflects the intrinsic crystal structure even at long electronic wavelengths. This effect requires the presence of Rashba SOI, where different group velocities depend on the chirality of the electronic states, mimicking the light polarization dependence of the group velocities in optical birefringent materials. This can in principle be achieved via gated regions, and result in the formation of spinful cusps and caustics caused by the Veselago lens defined by the gate. Interestingly, this would be evident by the doubling of caustics and cusps produced by circular birefringent lenses, where the spacing between the two different chiral cusps is proportional to the strength of the Rashba interaction in the system [3].