Long-range nontopological edge currents in charge-neutral graphene

• Published in: Nature (London) 2021-05, Vol.593 (7860), p.528-534
• Main Authors: Aharon-Steinberg, A., Marguerite, A., Perello, D. J., Bagani, K., Holder, T., Myasoedov, Y., Levitov, L. S., Geim, A. K., Zeldov, E.
• Format: Article
• Language: English
• Subjects: 142/126; 142/136; 639/301/119/2794; 639/301/119/995; 639/766/119/1000/1018; 639/925/918/1052; 639/925/930/2735; Condensed Matter; Conductance; Current carriers; Decoupling; Electric contacts; Electric currents; Electric fields; Electric properties; Electron states; Electronic systems; Expected values; Flow distribution; Flow pattern; Graphene; Helical flow; Heterostructures; Humanities and Social Sciences; Magnetic fields; Mesoscopic Systems and Quantum Hall Effect; multidisciplinary; Neutrality; Observations; Physics; Resistance; Science; Science (multidisciplinary); Superconducting quantum interference devices; Transition metals
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-021-03501-7

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 moiré 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.