Anomalous Quantum Oscillations in a Heterostructure of Graphene on a Proximate Quantum Spin Liquid

TL;DR

This paper develops a microscopic theory explaining anomalous quantum oscillations observed in a graphene/1-RuCl heterostructure, revealing how fractionalized spin excitations influence electronic properties beyond standard models.

Contribution

It introduces a Kitaev-Kondo lattice model to describe the interaction between graphene electrons and a proximate quantum spin liquid, explaining anomalous quantum oscillations.

Findings

The model reproduces the non-Lifshitz-Kosevich temperature dependence of QOs.

Remnants of fractionalized spin excitations produce characteristic QO signatures.

Ab-initio calculations support the microscopic parameters used in the theory.

Abstract

The quasi two-dimensional Mott insulator $\alpha$-RuCl$_3$ is proximate to the sought-after Kitaev quantum spin liquid (QSL). In a layer of $\alpha$-RuCl$_3$ on graphene the dominant Kitaev exchange is further enhanced by strain. Recently, quantum oscillation (QO) measurements of such $\alpha$-RuCl$_3$ / graphene heterostructures showed an anomalous temperature dependence beyond the standard Lifshitz-Kosevich (LK) description. Here, we develop a theory of anomalous QO in an effective Kitaev-Kondo lattice model in which the itinerant electrons of the graphene layer interact with the correlated magnetic layer via spin interactions. At low temperatures a heavy Fermi liquid emerges such that the neutral Majorana fermion excitations of the Kitaev QSL acquire charge by hybridising with the graphene Dirac band. Using ab-initio calculations to determine the parameters of our low energy model we provide a microscopic theory of anomalous QOs with a non-LK temperature dependence consistent with our measurements. We show how remnants of fractionalized spin excitations can give rise to characteristic signatures in QO experiments.