Robust fractional quantum Hall effect in the N=2 Landau level in bilayer graphene

Abstract

The fractional quantum Hall effect is a canonical example of electron–electron interactions producing new ground states in many-body systems. Most fractional quantum Hall studies have focussed on the lowest Landau level, whose fractional states are successfully explained by the composite fermion model. In the widely studied GaAs-based system, the composite fermion picture is thought to become unstable for the N≥2 Landau level, where competing many-body phases have been observed. Here we report magneto-resistance measurements of fractional quantum Hall states in the N=2 Landau level (filling factors 4<|ν|<8) in bilayer graphene. In contrast with recent observations of particle–hole asymmetry in the N=0/N=1 Landau levels of bilayer graphene, the fractional quantum Hall states we observe in the N=2 Landau level obey particle–hole symmetry within the fully symmetry-broken Landau level. Possible alternative ground states other than the composite fermions are discussed.

Effective Landau Level Diagram of Bilayer Graphene

“…In bilayer graphene, the valley and isospin degrees of freedom increase the number of potential many-body coherent ground states. Furthermore, the impact of actively controlling these degrees of freedom became evident in the recent observations of fractional and even-denominator fractional quantum Hall effects [17,[21][22][23][24][25].…”

“…In bilayer graphene, the valley and isospin degrees of freedom increase the number of potential many-body coherent ground states. Furthermore, the impact of actively controlling these degrees of freedom became evident in the recent observations of fractional and even-denominator fractional quantum Hall effects [17,[21][22][23][24][25].A good starting point of exploring this rich landscape would be a single-particle, or single-particlelike LL diagram, upon which interaction effects can be elucidated perturbatively. Indeed, even in the inherently strongly interacting fractional quantum Hall effect, effective single-particle models, e.g.…”

Recent Advances in Quantum Effects of 2D Materials

“…As for FQHE, the experimental observation requires much more extreme conditions, such as the ultra‐clean sample, extremely low temperature and very strong B‐ field. Till now, the observation of FQHE has been demonstrated in suspended SLG, BLG, and TwBG, but the underlying physical mechanism is rather intricate and beyond the scope of this review.…”

Bilayer Graphene as the Material for Study of the Unconventional Fractional Quantum Hall Effect

“…In dotted frames, fitting with the hierarchy given in Table 2 is added. [ [10][11][12][13][14]. Surprisingly, the FQHE state at ν ¼À 1 2 observed in bilayer structure on BN substrate disappears in the suspended sample of bilayer graphene.…”

“…Easy methods for the manufacturing of monolayer and bilayer graphene ought to be experimentally noticeable. And indeed, several recent observations of FQHE in bilayer graphene [10][11][12][13][14] demonstrate strong distinctions in comparison to FQHE hierarchy in monolayer graphene [15][16][17][18].…”