Observation of Electron Coherence and Fabry-Perot Standing Waves at a Graphene Edge

Monica T. Allen*, Oles Shtanko, Ion C. Fulga, Joel I.J. Wang, Daniyar Nurgaliev, Kenji Watanabe, Takashi Taniguchi, Anton R. Akhmerov, Pablo Jarillo-Herrero, Leonid S. Levitov, Amir Yacoby

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

20 Citations (Scopus)
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Electron surface states in solids are typically confined to the outermost atomic layers and, due to surface disorder, have negligible impact on electronic transport. Here, we demonstrate a very different behavior for surface states in graphene. We probe the wavelike character of these states by Fabry-Perot (FP) interferometry and find that, in contrast to theoretical predictions, these states can propagate ballistically over micron-scale distances. This is achieved by embedding a graphene resonator formed by gate-defined p-n junctions within a graphene superconductor-normal-superconductor structure. By combining superconducting Aharanov-Bohm interferometry with Fourier methods, we visualize spatially resolved current flow and image FP resonances due to p-n-p cavity modes. The coherence of the standing-wave edge states is revealed by observing a new family of FP resonances, which coexist with the bulk resonances. The edge resonances have periodicity distinct from that of the bulk states manifest in a repeated spatial redistribution of current on and off the FP resonances. This behavior is accompanied by a modulation of the multiple Andreev reflection amplitude on-and-off resonance, indicating that electrons propagate ballistically in a fully coherent fashion. These results, which were not anticipated by theory, provide a practical route to developing electron analog of optical FP resonators at the graphene edge.

Original languageEnglish
Pages (from-to)7380-7386
Number of pages7
JournalNano Letters: a journal dedicated to nanoscience and nanotechnology
Issue number12
Publication statusPublished - 13 Dec 2017


  • Ballistic transport
  • electron optics
  • Fabry-Perot interference
  • graphene edge states
  • Josephson interferometry


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