Gate-tunable proximity effects in graphene on layered magnetic insulators

TL;DR

This study explores gate-tunable proximity effects in graphene layered with magnetic insulators, revealing charge transfer and unusual transport phenomena without direct magnetic exchange, and demonstrating control via gating and magnetic state switching.

Contribution

It uncovers unprecedented gate-tunable proximity effects in graphene on layered magnetic insulators, highlighting charge transfer and transport anomalies, and shows gating can suppress these effects.

Findings

Graphene exhibits charge transfer from magnetic insulators leading to hole doping.

Transport features include extended quantum Hall plateaus and Landau level reversals.

Gating can suppress charge transfer and alter magnetic states in the heterostructures.

Abstract

The extreme versatility of two-dimensional van der Waals (vdW) materials derives from their ability to exhibit new electronic properties when assembled in proximity with dissimilar crystals. For example, although graphene is inherently non-magnetic, recent work has reported a magnetic proximity effect in graphene interfaced with magnetic substrates, potentially enabling a pathway towards achieving a high-temperature quantum anomalous Hall effect. Here, we investigate heterostructures of graphene and chromium trihalide magnetic insulators (CrI$_3$, CrBr$_3$, and CrCl$_3$). Surprisingly, we are unable to detect a magnetic exchange field in the graphene, but instead discover proximity effects featuring unprecedented gate-tunability. The graphene becomes highly hole-doped due to charge transfer from the neighboring magnetic insulator, and further exhibits a variety of atypical transport features. These include highly extended quantum Hall plateaus, abrupt reversals in the Landau level filling sequence, and hysteresis over at least days-long time scales. In the case of CrI$_3$, we are able to completely suppress the charge transfer and all attendant atypical transport effects by gating. The charge transfer can additionally be altered in a first-order phase transition upon switching the magnetic states of the nearest CrI$_3$ layers. Our results provide a roadmap for exploiting the magnetic proximity effect in graphene, and motivate further experiments with other magnetic insulators.