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HL: Fachverband Halbleiterphysik

HL 81: Graphene: Transport incl. Spin Physics and Magnetic Fields I

HL 81.1: Vortrag

Donnerstag, 29. März 2012, 15:00–15:15, ER 270

Aharonov-Bohm effect in an electron -hole graphene system — •Dmitri Smirnov, Hennrik Schmidt, and Rolf J. Haug — Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstr. 2 30167 Hannover, Germany

We analyze the electronic properties of a monolayer graphene ring. The sample and structured by standard procedures: micro-mechanical cleavage for preparation on a Si-wafer with a 285 nm thick layer of SiO2, electron beam lithography, active oxygen etching for structuring and contacting the ring shaped sample. The sample is measured in a He3-cryostat system with a base temperature of 500 mK and is identified as monolayer first via optical microscopy and later based on the magnetotransport measurements. In addition to the Si-backgate we place a topgate on top of one arm of the ring to manipulate the charge carrier concentration and to be able to create a pnp- (npn-) junction inside the ring. We observe Aharonov-Bohm oscillations by variation of the magnetic field around 0 T. The period of the oscillation is approx. 16.5 mT and fits the size of the ring well. The maximum visibility of the oscillations in all measurements is about 1%. We are also able to observe the oscillations when a pnp-junction is created inside the ring. The period is independent of the existence of a pnp-junction and stays constant in all situations. We analyze the amplitude in dependence of the charge carrier type and concentration. The absolute amplitude is constant in the bipolar and unipolar region. The relative amplitude has a dependence that is based on the changing background resistance.