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

Abstract

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 cm^2V^-1s^-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 1K. 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
Volume11
Issue number1
DOIs
Publication statusPublished - 1 Dec 2020