Measuring the pseudo-spin space of hydrogenated graphene – Thomas Szkopek, McGill

Thomas Szkopek, Dept. of Electrical and Computer Engineering, McGill, Montréal, QC, Canada

We have observed the quantum Hall effect (QHE) and Shubnikov-de Haas (SdH) oscillations in millimetre scale hydrogenated graphene. We find that the pseudo-spin structure of graphene is remarkably robust to the sub-lattice symmetry breaking induced by hydrogenation. Hydrogenation of pristine graphene is experimentally observed to increase electrical resistance and introduce neutral point defects as evidenced by Raman spectroscopy. In the highly resistive limit, strongly insulating behaviour is observed with a typical 2-pt resistance of 250 h/e2 at low temperature, far above the Ioffe-Regel limit for metallic conduction. Upon application of a magnetic field, colossal negative magnetoresistance is observed with the emergence of a nu = -2 QHE state at 45 T from an insulating state, with the notable absence of SdH oscillations ( J. Guillemette et al, Phys. Rev. Lett. 110, 176801 (2013) ). The rapid collapse of resistance is observed to occur when the magnetic length is comparable to the mean spacing of neutral point defects. We have observed SdH oscillations in hydrogenated graphene with lower resistivity at magnetic fields up to 55 T. Analysis of SdH oscillation frequency in 1/B indicates that the Landau level (LL) sequence remains four-fold degenerate as in pristine graphene. We also observe the nu = -2 QHE state in all samples. We therefore conclude that the topological part of the Berry phase, meaning the pseudo-spin winding number that determines the LL sequence, is preserved upon hydrogenation in large scale graphene. 

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Cette conférence est présentée par le RQMP Versant Nord du Département de physique de l'Université de Montréal et le Département de génie physique de Polytechnique Montréal.