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

Autor: Barrier J; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Kumaravadivel P; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Krishna Kumar R; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Ponomarenko LA; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; Department of Physics, University of Lancaster, Lancaster, LA1 4YW, UK., Xin N; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Holwill M; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Mullan C; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK., Kim M; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK., Gorbachev RV; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Thompson MD; Department of Physics, University of Lancaster, Lancaster, LA1 4YW, UK., Prance JR; Department of Physics, University of Lancaster, Lancaster, LA1 4YW, UK., Taniguchi T; National Institute for Materials Science, Ibaraki, 305-0044, Japan., Watanabe K; National Institute for Materials Science, Ibaraki, 305-0044, Japan., Grigorieva IV; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Novoselov KS; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Mishchenko A; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Fal'ko VI; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK., Geim AK; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK. geim@manchester.ac.uk.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK. geim@manchester.ac.uk., Berdyugin AI; Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK. alexey.berdyugin@manchester.ac.uk.; National Graphene Institute, University of Manchester, Manchester, M13 9PL, UK. alexey.berdyugin@manchester.ac.uk.
Jazyk: angličtina
Zdroj: Nature communications [Nat Commun] 2020 Nov 13; Vol. 11 (1), pp. 5756. Date of Electronic Publication: 2020 Nov 13.
DOI: 10.1038/s41467-020-19604-0
Abstrakt: 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 10 6  cm 2  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.
Databáze: MEDLINE