Observation of the quantum valley Hall state in ballistic graphene superlattices

TL;DR

This paper reports the observation of a quantum valley Hall state in ballistic graphene superlattices, revealing long-range charge-neutral currents and non-local resistance phenomena without magnetic fields, and explores their behavior under varying conditions.

Contribution

It introduces the first experimental observation of a quantum valley Hall state in ballistic graphene superlattices, demonstrating non-local resistance and valley/pseudospin magnetism effects.

Findings

Observation of giant non-local resistance with a large valley Hall angle

Emergence of a quantum valley Hall state at low temperatures

Non-local resistance plateau indicating qVHS rigidity and its collapse under magnetic field

Abstract

In graphene superlattices, bulk topological currents can lead to long-range charge-neutral flow and non-local resistance near Dirac points. A ballistic version of these phenomena has never been explored. Here, we report transport properties of ballistic graphene superlattices. This allows us to study and exploit giant non-local resistances with a large valley Hall angle without a magnetic field. In the low-temperature regime, a crossover occurs toward a new state of matter, referred to as a quantum valley Hall state (qVHS), which is an analog of the quantum Hall state without a magnetic field. Furthermore, a non-local resistance plateau, implying rigidity of the qVHS, emerges as a function of magnetic field, and the collapse of this plateau is observed, which is considered as a manifestation of valley/pseudospin magnetism.