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

Julien Barrier, Piranavan Kumaravadivel, Roshan Krishna Kumar, L. A. Ponomarenko, Na Xin, Matthew Holwill, Ciaran Mullan, Minsoo Kim, R. V. Gorbachev, M. D. Thompson, J. R. Prance, T. Taniguchi, K. Watanabe, I. V. Grigorieva, K. S. Novoselov, A. Mishchenko, V. I. Fal’ko, A. K. Geim () and A. I. Berdyugin ()
Additional contact information
Julien Barrier: University of Manchester
Piranavan Kumaravadivel: University of Manchester
Roshan Krishna Kumar: University of Manchester
L. A. Ponomarenko: University of Manchester
Na Xin: University of Manchester
Matthew Holwill: University of Manchester
Ciaran Mullan: University of Manchester
Minsoo Kim: University of Manchester
R. V. Gorbachev: University of Manchester
M. D. Thompson: University of Lancaster
J. R. Prance: University of Lancaster
T. Taniguchi: National Institute for Materials Science
K. Watanabe: National Institute for Materials Science
I. V. Grigorieva: University of Manchester
K. S. Novoselov: University of Manchester
A. Mishchenko: University of Manchester
V. I. Fal’ko: University of Manchester
A. K. Geim: University of Manchester
A. I. Berdyugin: University of Manchester

Nature Communications, 2020, vol. 11, issue 1, 1-7

Abstract: 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 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.

Date: 2020
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DOI: 10.1038/s41467-020-19604-0

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