Cascade of Even-Denominator Fractional Quantum Hall States in Mixed-Stacked Multilayer Graphene

TL;DR

This paper reports the discovery of a cascade of even-denominator fractional quantum Hall states in mixed-stacked multilayer graphene, revealing tunable non-Abelian topological phases with potential for quantum computing applications.

Contribution

It demonstrates the observation of high-filling half-filled FQH states in a new graphene system, with unprecedented tunability and evidence of non-Abelian Moore-Read states.

Findings

Observation of even-denominator FQH states at multiple filling factors

High displacement field tunability via Landau level crossings

Numerical evidence of non-Abelian Moore-Read type states

Abstract

The fractional quantum Hall effect (FQHE), particularly at half-filling of Landau levels, provides a unique window into topological phases hosting non-Abelian excitations. However, experimental platforms simultaneously offering large energy gaps, delicate tunability, and robust non-Abelian signatures remain scarce. Here, we report the observation of a cascade of even-denominator FQH states at filling factors ${\nu}$ = ${-5/2}$, ${-7/2}$, ${-9/2}$, ${-11/2}$, and ${-13/2}$, alongside numerous odd-denominator states in mixed-stacked pentalayer graphene, a previously unexplored system characterized by intertwined quadratic and cubic band dispersions. These even-denominator states, representing the highest filling half-filled states reported so far in the zeroth Landau level (ZLL), emerge from two distinct intra-ZLL and exhibit unprecedented displacement field tunability driven by LL crossings in the hybridized multiband structure. At half fillings, continuous quasiparticle phase transitions between paired FQH states, magnetic Bloch states, and composite Fermi liquids are clearly identified upon tuning external fields. Numerical calculations, revealing characteristic sixfold ground-state degeneracy and chiral graviton spectral analysis, suggest the observed even-denominator FQH states belong to the non-Abelian Moore-Read type. These results establish mixed-stacked multilayer graphene as a rich and versatile crystalline platform for exploring tunable correlated topological phases.