Bilayer graphene. Electron-hole asymmetric integer and fractional quantum Hall effect in bilayer graphene.

A Kou,A J Levin,A Yacoby,T Taniguchi,B I Halperin,K Watanabe,B E Feldman

doi:10.1126/science.1250270

A Kou, A J Levin + Show 5 more

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https://doi.org/10.1126/science.1250270

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Abstract

The nature of fractional quantum Hall (FQH) states is determined by the interplay between the Coulomb interaction and the symmetries of the system. The distinct combination of spin, valley, and orbital degeneracies in bilayer graphene is predicted to produce an unusual and tunable sequence of FQH states. Here, we present local electronic compressibility measurements of the FQH effect in the lowest Landau level of bilayer graphene. We observe incompressible FQH states at filling factors ν = 2p + 2/3, with hints of additional states appearing at ν = 2p + 3/5, where p = -2, -1, 0, and 1. This sequence breaks particle-hole symmetry and obeys a ν → ν + 2 symmetry, which highlights the importance of the orbital degeneracy for many-body states in bilayer graphene.

Highlights

The charge carriers in bilayer graphene obey an electron-hole symmetric dispersion at zero magnetic field
The interplay between externally applied fields and intrinsic electron-electron interactions, both of which break the degeneracies of bilayer graphene, produces a rich phase diagram not found in any other system
All of the integer broken-symmetry states have fully developed at these magnetic fields, and averaging over a range of fields helps to clarify the underyling behavior of the inverse compressibility by reducing fluctuations caused by localized states

Summary

Introduction

The charge carriers in bilayer graphene obey an electron-hole symmetric dispersion at zero magnetic field. Partial breaking of the SU[4] symmetry in monolayer graphene has already resulted in sequences of FQH states with multiple missing fractions [17,18,19,20,21,22].

Results

Conclusion