Sreda, 21. novembar 2012. godine u 11 casova u sali 661 na Fizickom fakultetu, Studentski trg 12, III sprat

“Edge magneto-plasmons in graphene”
Dr Ivana Petković
Nanoelectronics Group, Service de Physique de l'Etat Condensé, CEA Saclay, F-91191, Gif-sur-Yvette, France;
Department of Physics, Yale University, New Haven, Connecticut 06520, USA

Abstract: The important physics for the quantum Hall effect (QHE) takes place on the edge of a 2-dimensional electron system (2DES), where dissipationless chiral transport current flows, Hall charge accumulates and the associated collective modes concentrate. The latter - Edge Magneto-Plasmons (EMP) - are quasi one dimensional elementary excitations which are split off from the bulk magneto-plasmon modes by the sample boundary. Closely confined to the edge as frequency is increased, they have been a tool of choice to investigate edge structure and dynamics of conventional 2-dimensional electron systems. The group velocity of these modes has two contributions, arising from the Hall conductivity and the carrier drift at the edge.  In graphene, due to its particular dynamics and an abrupt edge, the drift velocity is expected to be of the order of the Fermi velocity, thus becoming experimentally accessible. We show EMP to exist by timing the travel of narrow wave-packets on picosecond time scales around exfoliated samples. We find chiral propagation with low attenuation at a velocity which is quantized on Hall plateaus. We extract the carrier drift contribution from the EMP propagation and find it to be slightly less than the Fermi velocity, as expected for an abrupt edge. We also extract the spatial spread of edge accumulated charge and find it to be narrower than for soft edge systems.