Lifting of the Landau level degeneracy in graphene devices in a tilted magnetic field

Abstract

We report on transport and capacitance measurements of graphene devices in magnetic fields up to 30 T. In both techniques, we observe the full splitting of Landau levels and we employ tilted field experiments to address the origin of the observed broken symmetry states. In the lowest energy level, the spin degeneracy is removed at filling factors $\ensuremath{\nu}=\ifmmode\pm\else\textpm\fi{}1$ and we observe an enhanced energy gap. In the higher levels, the valley degeneracy is removed at odd filling factors while spin polarized states are formed at even $\ensuremath{\nu}$. Although the observation of odd filling factors in the higher levels points towards the spontaneous origin of the splitting, we find that the main contribution to the gap at $\ensuremath{\nu}=\ensuremath{-}4,\ensuremath{-}8$, and $\ensuremath{-}12$ is due to the Zeeman energy.