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URL:https://murmitoyen.com/events/vanille/udem/detail/370356
LOCATION:Université de Montréal - Pavillon J.-Armand-Bombardier\, 5155\, 
 chemin de la rampe \, Montréal\, QC\, Canada\, H3T 2B2
SUMMARY: Measuring the pseudo-spin space of hydrogenated graphene – Thoma
 s Szkopek\, McGill
DESCRIPTION:Thomas Szkopek\, Dept. of Electrical and Computer Engineering\,
  McGill\, Montréal\, QC\, CanadaWe have observed the quantum Hall effect
  (QHE) and Shubnikov-de Haas (SdH) oscillations in millimetre scale hydrog
 enated graphene. We find that the pseudo-spin structure of graphene is rem
 arkably robust to the sub-lattice symmetry breaking induced by hydrogenati
 on. Hydrogenation of pristine graphene is experimentally observed to incre
 ase electrical resistance and introduce neutral point defects as evidenced
  by Raman spectroscopy. In the highly resistive limit\, strongly insulatin
 g 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. Upo
 n application of a magnetic field\, colossal negative magnetoresistance is
  observed with the emergence of a nu = -2 QHE state at 45 T from an insula
 ting state\, with the notable absence of SdH oscillations ( J. Guillemette
  et al\, Phys. Rev. Lett. 110\, 176801 (2013) ). The rapid collapse of res
 istance 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 5
 5 T. Analysis of SdH oscillation frequency in 1/B indicates that the Landa
 u level (LL) sequence remains four-fold degenerate as in pristine graphene
 . We also observe the nu = -2 QHE state in all samples. We therefore concl
 ude that the topological part of the Berry phase\, meaning the pseudo-spin
  winding number that determines the LL sequence\, is preserved upon hydrog
 enation in large scale graphene. Site web du groupe du  Prof. SzkopekCet
 te conférence est présentée par le RQMP Versant Nord du Département d
 e physique de l'Université de Montréal et le Département de génie phys
 ique de Polytechnique Montréal.
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