Tuning the Pseudospin Polarization of Graphene by a Pseudomagnetic Field

Alexander Georgi, Peter Nemes-Incze, Ramon Carrillo-Bastos, Daiara Faria, Silvia Viola Kusminskiy, Dawei Zhai, Martin Schneider, Dinesh Subramaniam, Torge Mashoff, Nils M. Freitag, Marcus Liebmann, Marco Pratzer, Ludger Wirtz, Colin R. Woods, Roman V. Gorbachev, Yang Cao, Kostya S. Novoselov, Nancy Sandler, Markus Morgenstern

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

One of the intriguing characteristics of honeycomb lattices is the appearance of a pseudomagnetic field as a result of mechanical deformation. In the case of graphene, the Landau quantization resulting from this pseudomagnetic field has been measured using scanning tunneling microscopy. Here we show that a signature of the pseudomagnetic field is a local sublattice symmetry breaking observable as a redistribution of the local density of states. This can be interpreted as a polarization of graphene's pseudospin due to a strain induced pseudomagnetic field, in analogy to the alignment of a real spin in a magnetic field. We reveal this sublattice symmetry breaking by tunably straining graphene using the tip of a scanning tunneling microscope. The tip locally lifts the graphene membrane from a SiO2 support, as visible by an increased slope of the I(z) curves. The amount of lifting is consistent with molecular dynamics calculations, which reveal a deformed graphene area under the tip in the shape of a Gaussian. The pseudomagnetic field induced by the deformation becomes visible as a sublattice symmetry breaking which scales with the lifting height of the strained deformation and therefore with the pseudomagnetic field strength. Its magnitude is quantitatively reproduced by analytic and tight-binding models, revealing fields of 1000 T. These results might be the starting point for an effective THz valley filter, as a basic element of valleytronics.

Original languageEnglish
Pages (from-to)2240-2245
Number of pages6
JournalNano letters
Volume17
Issue number4
DOIs
Publication statusPublished - Apr 12 2017

Keywords

  • Graphene
  • STM
  • pseudomagnetic field
  • pseudospin polarization
  • strain
  • valley filter

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering

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  • Cite this

    Georgi, A., Nemes-Incze, P., Carrillo-Bastos, R., Faria, D., Viola Kusminskiy, S., Zhai, D., Schneider, M., Subramaniam, D., Mashoff, T., Freitag, N. M., Liebmann, M., Pratzer, M., Wirtz, L., Woods, C. R., Gorbachev, R. V., Cao, Y., Novoselov, K. S., Sandler, N., & Morgenstern, M. (2017). Tuning the Pseudospin Polarization of Graphene by a Pseudomagnetic Field. Nano letters, 17(4), 2240-2245. https://doi.org/10.1021/acs.nanolett.6b04870