Landau level splittings, phase transitions, and non-uniform charge distribution in trilayer graphene

TL;DR

This study investigates the quantum Hall effect and Landau level splittings in dual-gated trilayer graphene, revealing phase transitions and charge density imbalances that enhance understanding of its electronic structure.

Contribution

It provides a theoretical model explaining Landau level splittings and phase transitions in trilayer graphene, emphasizing the role of charge imbalance and a new band structure parameter.

Findings

Complete lifting of Landau level degeneracy observed.

Sequence of quantum Hall phase transitions with electric field.

Charge density imbalance between layers at neutrality.

Abstract

We report on magneto-transport studies of dual-gated, Bernal-stacked trilayer graphene (TLG) encapsulated in boron nitride crystals. We observe a quantum Hall effect staircase which indicates a complete lifting of the twelve-fold degeneracy of the zeroth Landau level. As a function of perpendicular electric field, our data exhibits a sequence of phase transitions between all integer quantum Hall states in the filling factor interval $-8<\nu<0$. We develop a theoretical model and argue that, in contrast to monolayer and bilayer graphene, the observed Landau level splittings and quantum Hall phase transitions can be understood within a single-particle picture, but imply the presence of a charge density imbalance between the inner and outer layers of TLG, even at charge neutrality and zero transverse electric field. Our results indicate the importance of a previously unaccounted band structure parameter which, together with a more accurate estimate of the other tight-binding parameters, results in a significantly improved determination of the electronic and Landau level structure of TLG.