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HL: Fachverband Halbleiterphysik

HL 53: Transport properties

HL 53.3: Vortrag

Freitag, 27. März 2009, 10:45–11:00, POT 151

Tuning of decoupled graphene layers by front and backgate — •Thomas Lüdtke, Hennrik Schmidt, Patrick Barthold, and Rolf J. Haug — Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstr. 2, 30167 Hannover

We present transport measurements through a heterojunction of decoupled layers of graphene as a function of backgate and topgate voltage as well as magnetic field at temperatures down to 300mK [1]. Folded monolayers on a SiO2 substrate are structured and contacted by using electron beam lithography. A PMMA layer is deposited onto the structured part to be able to fabricate an additional local gate afterwards.

In a four terminal measurement the resistance of the device was obtained by tuning the potential of the backgate and the topgate independently. Charge neutrality points of both regions are clearly visible, separating the different charge configurations (e.g. p-n-p, n-n-n) of the graphene field effect transistor. The magnetic field dependence of the localy gated sample shows four different oscillations in the Shubnikov-de Haas (SdH) measurement. Two of these oscillations are dependent on the potential of the applied backgate, whereas the other two oscillations changes when tuning the local topgate. Calculations of the carrier concentrations from SdH measurements as well as a Berry phase of Pi shows the existence of two decoupled monolayers of graphene that can be tuned by gates independently.

[1] H. Schmidt, T. Lüdtke, P. Barthold, E. McCann, V. I. Fal'ko, and R. J. Haug; Appl. Phys. Lett. 93, 172108 (2008)