Transport measurements on ultra-clean dual-gated suspended bilayer graphene

J. Velasco Jr.¹, L. Jing¹, Y. Lee¹, P. Kratz², W. Bao¹, D. Smirnov³, M. Bockrath¹ and C. N. Lau¹

¹ Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA
² Department of Physics and Astronomy, Stanford University, Stanford, CA 94305, USA
³ National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA

Published online: 07 March 2012

Abstract

We fabricate ultra clean contactless dual-gated devices comprised of suspended bilayer graphene (BLG) and investigate their low temperature electron transport properties as functions of charge density n, magnetic field B and electric field E_⊥ We find that for devices with moderate mobility, conductance remains finite at the charge neutrality point and decreases monotonically with increasing |E_⊥|, as expected in the picture of single particle behavior. In contrast, devices with highest mobility display an insulating state at B=E_⊥=n=0, and conductance’s dependence on E_⊥ is non-monotonic. This surprising behavior arises from electronic interactions. In finite B, we observe quantum Hall plateaus with the 8-fold degeneracy of the lowest Landau level completely broken, as well as a fractional state.