Observation of ballistic upstream modes at fractional quantum Hall edges of graphene

Ravi Kumar, Saurabh Kumar Srivastav, Christian Spånslätt, K. Watanabe, T. Taniguchi, Yuval Gefen, Alexander D. Mirlin and Anindya Das ()
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Ravi Kumar: Indian Institute of Science
Saurabh Kumar Srivastav: Indian Institute of Science
Christian Spånslätt: Chalmers University of Technology
K. Watanabe: National Institute of Material Science
T. Taniguchi: National Institute of Material Science
Yuval Gefen: Weizmann Institute of Science
Alexander D. Mirlin: Karlsruhe Institute of Technology
Anindya Das: Indian Institute of Science

Nature Communications, 2022, vol. 13, issue 1, 1-7

Abstract: Abstract The presence of “upstream” modes, moving against the direction of charge current flow in the fractional quantum Hall (FQH) phases, is critical for the emergence of renormalized modes with exotic quantum statistics. Detection of excess noise at the edge is a smoking gun for the presence of upstream modes. Here, we report noise measurements at the edges of FQH states realized in dual graphite-gated bilayer graphene devices. A noiseless dc current is injected at one of the edge contacts, and the noise generated at contacts at length, L = 4 μm and 10 μm away along the upstream direction is studied. For integer and particle-like FQH states, no detectable noise is measured. By contrast, for “hole-conjugate” FQH states, we detect a strong noise proportional to the injected current, unambiguously proving the existence of upstream modes. The noise magnitude remains independent of length, which matches our theoretical analysis demonstrating the ballistic nature of upstream energy transport, quite distinct from the diffusive propagation reported earlier in GaAs-based systems.

Date: 2022
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DOI: 10.1038/s41467-021-27805-4

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