Influence of carrier density and disorder on the Quantum Hall plateau widths in epitaxial graphene

TL;DR

This study explores how carrier density, disorder, and mobility influence the widths of quantum Hall plateaus in epitaxial graphene, revealing that disorder and mobility significantly affect plateau extension beyond carrier density effects.

Contribution

It provides new experimental and simulation insights into how disorder and mobility interplay to determine quantum Hall plateau widths in graphene.

Findings

Mobility variations up to 200% observed due to storage conditions.

QHP extension for ν=6 varies significantly between regions with different mobility.

Disorder and mobility, not just carrier density, critically influence QHP widths.

Abstract

Since its discovery, graphene has been one of the most prominent 2D materials due to its unique properties and broad range of possible applications. In particular, the half-integer Quantum Hall Effect (HI-QHE) characterized by the quantization of Hall resistivity as a function of applied magnetic field, offers opportunities for advancements in quantum metrology and the understanding of topological quantum states in this 2D material. While the role of disorder in stabilizing quantum Hall plateaus (QHPs) is widely recognized, the precise interplay between the plateaus width, disorder, mobility and carrier density remains less explored. In this work, we investigate the width of the $\nu=6$ QHP in epitaxial graphene Hall bars, focusing on two distinct regions of the device with markedly different electronic mobilities. Depending on the storage conditions, it is possible to modify the carrier density of graphene QHE devices and consequently increase or reduce the mobility. Our experiments reveal mobility variations of up to 200$\%$ from their initial value. In particular, the sample storage time and ambient conditions cause also noticeable changes in the positions and extension of the QHPs. Our results show that the QHP extension for $\nu=6$ differs significantly between the two regions, influenced by both mobility and disorder, rather than solely by carrier density. Transport simulations based on the Landauer-B\"uttiker formalism with Anderson disorder in a scaled model reveal the critical role of impurities in shaping graphene transport properties defining the extension of the QHPs. This study provides valuable insights into the interplay between mobility, disorder, and quantum transport in graphene systems.