High magnetic fields reveal electron-electron interaction in graphene

Researchers from the University of Manchester, in collaboration with HFML scientists, have measured the quantum capacitance of ultra-clean graphene capacitors in high magnetic fields up to 30 T. In these experiments on devices with a hitherto unmatched quality it was possible to directly access the interaction between individual electrons which is normally masked by electron scattering with impurities in lower-quality graphene. The results are published on February 11 in Proceedings of the National Academy of Sciences (PNAS).

The researchers have performed capacitance measurements on graphene capacitors positioned on BN, caped with another thin BN layer and covered with a gold top-gate. Such experiments are a powerful tool to directly measure the electronic density of states and the high mobility makes it possible us to access the subtle influence of electron-electron interaction.

Indeed, already at zero magnetic field, an interaction-induced renormalization of the linear single-particle spectrum can be observed and in quantizing magnetic fields the spin- and valley-degenerate Landau levels split up into individual quartets. Interestingly, the energetic separation between these sub-levels is mainly interaction driven and no intrinsic Zeeman splitting is observed.

G. L. Yu, R. Jalil, Branson Belle, Alexander S. Mayorov, Peter Blake, Frederick Schedin, Sergey V. Morozov, Leonid A. Ponomarenko, F. Chiappini, S. Wiedmann, Uli Zeitler, Mikhail I. Katsnelson, A. K. Geim, Kostya S. Novoselov, and Daniel C. Elias, Interaction phenomena in graphene seen through quantum capacitance.
PNAS 2013; published ahead of print February 11, 2013.

Graphene capacitor

Micrograph of BN-graphene-BN-Au capacitor. A graphene flake (visible as a shadow) is sandwiched between two BN layers (bottom: dark gray / top: blue). The Au gate on the top BN flake (not visible) and the graphene flake are contacted with the grey contact pads.
Credits: University of Manchester.