Non-Hermitian topology in the quantum Hall effect of graphene

TL;DR

This paper demonstrates tunable non-Hermitian topological phases in graphene's quantum Hall effect, revealing novel properties and phases that could enhance topological device performance.

Contribution

It introduces gate voltage control of non-Hermitian topology in graphene, uncovering new phases and optimizing topological invariants for device applications.

Findings

High filling factor yields best non-Hermitian topological quantization

An additional non-Hermitian phase exists in the nu=0 plateau

Disorder-induced trivial phase confirmed at lower fields

Abstract

Quantum Hall phases have recently emerged as a platform to investigate non-Hermitian topology in condensed-matter systems. This platform is particularly interesting due to its tunability, which allows to modify the properties and topology of the investigated non-Hermitian phases by tuning external parameters of the system such as the magnetic field. Here, we show the tunability of non-Hermitian topology chirality in a graphene heterostructure using a gate voltage. By changing the charge carrier density, we unveil some novel properties specific to different quantum Hall regimes. First, we find that the best quantization of the non-Hermitian topological invariant is interestingly obtained at very high filling factor rather than on well-quantized quantum Hall plateaus. This is of particular importance for the efficient operation of devices based on non-Hermitian topology. Moreover, we observe an additional non-Hermitian topological phase in the insulating nu=0 quantum Hall plateau, which survives at lower fields than the opening of the nu=0 gap, confirming a recent prediction of a disorder-induced trivial phase. Our results evidence graphene as a promising platform for the study of non-Hermitian physics and of emergent phases in such topological devices.