Observation of even denominator fractional quantum Hall effect in suspended bilayer graphene

TL;DR

This study reports the first observation of an even-denominator fractional quantum Hall state at nu = -1/2 in suspended bilayer graphene, revealing new insights into quantum Hall phenomena and Landau level degeneracy effects.

Contribution

The paper presents the experimental discovery of an even-denominator fractional quantum Hall state in bilayer graphene, supported by high-precision measurements and theoretical consistency.

Findings

Observation of a quantized plateau at nu = -1/2 with 0.5% precision

Identification of multiple fractional quantum Hall states in bilayer graphene

Support for a Moore-Read type state due to Landau level degeneracy

Abstract

We investigate low-temperature magneto-transport in recently developed, high-quality multi-terminal suspended bilayer graphene devices, enabling the independent measurement of the longitudinal and transverse resistance. We observe clear signatures of the fractional quantum Hall effect, with different states that are either fully developed, and exhibit a clear plateau in the transverse resistance with a concomitant dip in longitudinal resistance, or incipient, and exhibit only a longitudinal resistance minimum. All observed states scale as a function of filling factor nu, as expected. An unprecedented even-denominator fractional state is observed at nu = -1/2 on the hole side, exhibiting a clear plateau in Rxy quantized at the expected value of 2h/e^2 with a precision of ~0.5%. Many of our observations, together with a recent electronic compressibility measurement performed in graphene bilayers on hexagonal boron-nitride (hBN) substrates, are consistent with a recent theory that accounts for the effect of the degeneracy between the N=0 and N=1 Landau levels in the fractional quantum Hall effect, and predicts the occurrence of a Moore-Read type nu = -1/2 state. Owing to the experimental flexibility of bilayer graphene --which has a gate-dependent band structure, can be easily accessed by scanning probes, and can be contacted with materials such as superconductors--, our findings offer new possibilities to explore the microscopic nature of even-denominator fractional quantum Hall effect.