Dong-Keun Ki, Vladimir I. Fal'ko, Alberto F. Morpurgo
In high quality two-dimensional electron systems (2DESs) subjected to a perpendicular magnetic field (B), the transverse Hall conductance G_{xy} exhibits plateaus at fractions of e^2/h, a phenomenon known as the fractional quantum Hall effect (FQHE). These fractions typically have an odd denominator and occur in hierarchical sequences that are understood theoretically. In few exceptional cases, and only in the highest quality GaAs-based heterostructures, even-denominator states have been observed whose microscopic nature is not well understood. Here we demonstrate a new strategy to realize ultra-clean suspended, multi-terminal graphene devices, and use it to show the occurrence of clear FQHE in bilayer graphene. As an unexpected finding, we observe a robust even-denominator state at G_{xy} = 1/2 e^2/h. Next to demonstrating the ability to realize new multi-terminal suspended graphene devices relevant for a variety of different experiments, our findings open the possibility to exploit the experimental flexibility of bilayer graphene in the investigation of even-denominator FQHE.
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http://arxiv.org/abs/1305.4761
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