Detecting Topological Currents in Graphene Superlattices

TL;DR

This paper reports the experimental detection of topological valley currents in graphene superlattices, showing long-range, charge-neutral flow that can be controlled by gate voltage, with potential applications in valleytronics.

Contribution

First experimental observation of long-range topological valley currents in graphene superlattices, demonstrating their controllability and potential for information processing.

Findings

Nonlocal voltage observed near Dirac points at zero magnetic field.

Topological currents are comparable in strength to the applied current.

Gate voltage can control the long-range valley currents.

Abstract

Topological materials may exhibit Hall-like currents flowing transversely to the applied electric field even in the absence of a magnetic field. In graphene superlattices, which have broken inversion symmetry, topological currents originating from graphene's two valleys are predicted to flow in opposite directions and combine to produce long-range charge neutral flow. We observe this effect as a nonlocal voltage at zero magnetic field in a narrow energy range near Dirac points at distances as large as several microns away from the nominal current path. Locally, topological currents are comparable in strength to the applied current, indicating large valley-Hall angles. The long-range character of topological currents and their transistor-like control by gate voltage can be exploited for information processing based on the valley degrees of freedom.