The hybridization of Dirac cones with the 4f states of Eu removes the spin degeneracy of the π state, inducing the opening of a wide spin-dependent band gap at the Dirac point and creating a finite Berry curvature across the gap.
The article demonstrates that in the graphene/Eu/Ni heterostructure, the breaking of time-reversal symmetry induced by magnetic ordering paves the way for the emergence of exotic transport phenomena, such as the anomalous Hall effect. The strong electronic doping of the system due to the presence of Eu brings a van Hove singularity in graphene very close to the Fermi level, which interacts with the spin-polarized valence states of Eu and becomes spin-polarized itself.
Our ARPES measurements and many-body model reveal the presence of a kink and a satellite feature due to electron-phonon coupling and the strong doping of the system caused by the Eu atoms.
These results pave the way for transforming graphene into a spin field-effect transistor, a spin valve, or a spin-transfer torque device, as well as realizing unconventional superconductivity, quantum phases, or topological insulator states in graphene.
This work is a collaboration of CNR-ISM with CNR-IOM, University of Calabria, Forschungszentrum Jülich and JARA, Ca’ Foscari University of Venice, Elettra Sincrotrone, and ICTP.