Long-range nontopological edge currents in charge-neutral graphene

Van der Waals heterostructures display numerous unique electronic properties. Nonlocal measurements, wherein a voltage is measured at contacts placed far away from the expected classical flow of charge carriers, have been widely used in the search for novel transport mechanisms, including dissipationless spin and valley transport(1-9), topological charge-neutral currents(10-12), hydrodynamic flows(13) and helical edge modes(14-16). Monolayer(1-5,10,15-19), bilayer(9,11,14,20) and few-layer(21) graphene, transition-metal dichalcogenides(6,7) and moire superlattices(8,10,12) have been found to display pronounced nonlocal effects. However, the origin of these effects is hotly debated(3,11,17,22-24). Graphene, in particular, exhibits giant nonlocality at charge neutrality(1,15-19), a striking behaviour that has attracted competing explanations. Using a superconducting quantum interference device on a tip (SQUID-on-tip) for nanoscale thermal and scanning gate imaging(25), here we demonstrate that the commonly occurring charge accumulation at graphene edges(23,26-31) leads to giant nonlocality, producing narrow conductive channels that support long-range currents. Unexpectedly, although the edge conductance has little effect on the current flow in zero magnetic field, it leads to field-induced decoupling between edge and bulk transport at moderate fields. The resulting giant nonlocality at charge neutrality and away from it produces exotic flow patterns that are sensitive to edge disorder, in which charges can flow against the global electric field. The observed one-dimensional edge transport is generic and nontopological and is expected to support nonlocal transport in many electronic systems, offering insight into the numerous controversies and linking them to long-range guided electronic states at system edges. Nanoscale imaging of edge currents in charge-neutral graphene shows that charge accumulation can explain various exotic nonlocal transport measurements, bringing into question some theories about their origins.

Automated summary

Van der Waals heterostructures exhibit unique electronic properties and have been studied using nonlocal measurements. Graphene edges with charge accumulation are found to produce giant nonlocal effects, supporting long-range currents. Edge conductance affects current flow in moderate magnetic fields, leading to decoupling between edge and bulk transport. The observed exotic flow patterns are sensitive to edge disorder and can flow against the global electric field. Thus, edge transport in charge-neutral graphene can explain various nonlocal transport measurements.