Even denominator fractional quantum Hall states in the zeroth Landau level of monolayer-like band of ABA trilayer graphene

TL;DR

This paper reports the unexpected observation of even-denominator fractional quantum Hall states in the zeroth Landau level of ABA trilayer graphene, revealing new states stabilized by LL mixing and tunable via external fields.

Contribution

It demonstrates the emergence of even-denominator FQHSs in the N=0 Landau level of ABA trilayer graphene, a novel finding in a system with tunable LL mixing and broken inversion symmetry.

Findings

Robust FQHSs at ν=5/2 and 7/2 observed

Daughter states at ν=7/13 and 9/17 identified

States strengthened with increasing magnetic field

Abstract

The fractional quantum Hall (FQH) effect is a macroscopic manifestation of strong electron-electron interactions. Even denominator FQH states (FQHSs) at half-filling are particularly interesting as they are predicted to host non-Abelian excitations with non-trivial braiding statistics. Such states are predominantly observed in the $N=1$ Landau level (LL) of semiconductors such as GaAs. In this Letter, we report the unanticipated observation of even-denominator FQHSs in the $N=0$ LL of ABA trilayer graphene (TLG), a system characterized by tunable LL mixing and the absence of inversion symmetry. Notably, we find robust FQHSs at $\nu=5/2$ and $\nu=7/2$ when two LLs, originating from a monolayer-like band of TLG with different isospin indices, cross each other. These are flanked by the Levin-Halperin daughter states at $\nu=7/13$ and $\nu=9/17$, respectively, and further away, the standard series of Jain-sequence of composite fermions (CFs) is observed. The even-denominator FQHSs and their accompanying daughter states become stronger with increasing magnetic fields, while concomitantly, a weakening of the CF states is observed. We posit that the absence of inversion symmetry in the system gives rise to additional isospin interactions, which enhance LL mixing and soften the short-range part of the Coulomb repulsion, stabilizing the even-denominator FQHSs. In addition, we demonstrate that these states, along with their daughter states, can be finely tuned with an external displacement field that serves as an important tool to control the LL mixing in the system.