Hetero-Orbital Two-Component Fractional Quantum Hall States in Bilayer Graphene

TL;DR

This paper explores hetero-orbital two-component fractional quantum Hall states in bilayer graphene, revealing unique behaviors and robustness due to strong SU(2) anisotropic interactions, expanding understanding of FQH phenomena.

Contribution

It introduces and analyzes hetero-orbital two-component FQH states where orbital indices form pseudospins, differing from traditional homo-orbital states, with experimental and theoretical insights.

Findings

Distinct behaviors for parallel-flux and reverse-flux composite fermion states

Observation of a strong 2/5 FQH state over a wide magnetic field range

Abrupt disappearance of the 2/5 state at high magnetic fields

Abstract

A two-dimensional electron system exposed to a strong magnetic field produces a plethora of strongly interacting fractional quantum Hall (FQH) states, the complex topological orders of which are revealed through exotic emergent particles, such as composite fermions, fractionally charged Abelian and non-Abelian anyons. Much insight has been gained by the study of multi-component FQH states, where spin and pseudospin indices of the electron contribute additional correlation. Traditional multi-component FQH states develop in situations where the components share the same orbital states and the resulting interactions are pseudospin independent; this homo-orbital nature was also crucial to their theoretical understanding. Here, we study "hetero-orbital" two-component FQH states, in which the orbital index is part of the pseudospin, rendering the multi-component interactions strongly SU(2) anisotropic in the pseudospin space. Such states, obtained in bilayer graphene at the isospin transition between N = 0 and N = 1 electron Landau levels, are markedly different from previous homo-orbital two-component FQH states. In particular, we observe strikingly different behaviors for the parallel-flux and reverse-flux composite fermion states, and an anomalously strong two-component 2/5 state over a wide range of magnetic field before it abruptly disappears at a high field. Our findings, combined with detailed theoretical calculations, reveal the surprising robustness of the hetero-orbital FQH effects, significantly enriching our understanding of FQH physics in this novel regime.