Long-range ballistic transport of Brown-Zak fermions in graphene superlattices

Research output: Contribution to journalArticlepeer-review

  • External authors:
  • Roshan Krishna Kumar
  • L. A. Ponomarenko
  • Na Xin
  • Matthew Holwill
  • Minsoo Kim
  • M. D. Tompson
  • J. R. Prance
  • T Taniguchi
  • K Watanabe
  • Konstantin Novoselov
  • Artem Mishchenko
  • Vladimir Fal'ko
  • Andre Geim
  • Alexey Berdyugin


In quantizing magnetic fields, graphene superlattices exhibit a complex fractal spectrum often referred to as the Hofstadter butterfly. It can be viewed as a collection of Landau levels that arise from quantization of Brown-Zak minibands recurring at rational (p/q) fractions of the magnetic flux quantum per superlattice unit cell. Here we show that, in graphene-on-boron-nitride superlattices, Brown-Zak fermions can exhibit mobilities above 106 cm2 V−1 s−1 and the mean free path exceeding several micrometers. The exceptional quality of our devices allows us to show that Brown-Zak minibands are 4q times degenerate and all the degeneracies (spin, valley and mini-valley) can be lifted by exchange interactions below 1 K. We also found negative bend resistance at 1/q fractions for electrical probes placed as far as several micrometers apart. The latter observation highlights the fact that Brown-Zak fermions are Bloch quasiparticles propagating in high fields along straight trajectories, just like electrons in zero field.

Bibliographical metadata

Original languageEnglish
Article number5756
JournalNature Communications
Issue number1
Publication statusPublished - 13 Nov 2020