2020/06/30 by Julien Barrier, Piranavan Kumaravadivel, Roshan Krishna-Kumar +18 · 39 citations
Materials Science · Physics and Astronomy · #Ballistic conduction #Degenerate energy levels #Electron #Fermion #Graphene #Graphene research and applications #Quantization (signal processing) #Quantum #Quantum and electron transport phenomena #Quasiparticle #Superlattice #Topological Materials and Phenomena #cond-mat.mes-hall
paper · pdf · doi:10.1038/s41467-020-19604-0
published in Nature Communications 11(1), 5756 (Nature Portfolio) · 16 pages, 13 figures
openalex created_date 2020/07/02 · arxiv created 2020/10/06 · openalex publication_date 2020/11/13 · arxiv updated 2020/11/16 · openalex updated_date 2026/08/05
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 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 4 q 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.