graphene; STM; strain; pseudomagnetic field; pseudospin polarization; valley filter
Abstract :
[en] 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.
Disciplines :
Physics
Author, co-author :
Georgi, Alexander; RWTH Aachen University > II. Institute of Physics B
Nemes-Incze, Peter; RWTH Aachen University > II. Institute of Physics B
Carrillo-Bastos, Ramon; Universidad Autónoma de Baja California > Facultad de Ciencias
Faria, Daiara; Universidade Federal Fluminense, Niterói, Rio de Janeiro > Instituto de Física
Kusminskiy, Silvia Viola; Freie Universität Berlin
Zhai, Dawei; Ohio University, Athens, Ohio > Department of Physics and Astronomy
Schneider, Martin; Freie Universität Berlin
Subramaniam, Dinesh; RWTH Aachen University > II. Institute of Physics B
Mashoff, Torge; Johannes Gutenberg-Universität Mainz
Freitag, Nils M.; RWTH Aachen University > II. Institute of Physics B
Liebmann, Marcus; RWTH Aachen University > II. Institute of Physics B
Pratzer, Marco; RWTH Aachen University > II. Institute of Physics B
WIRTZ, Ludger ; University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit
Woods, Colin R.; University of Manchester > School of Physics and Astronomy
Gorbachev, Roman V.; University of Manchester > School of Physics and Astronomy
Cao, Yang; University of Manchester > School of Physics and Astronomy
Novoselov, Kostya S.; University of Manchester > School of Physics and Astronomy
Sandler, Nancy; Ohio University, Athens, Ohio > Department of Physics and Astronomy
Morgenstern, Markus; RWTH Aachen University > II. Institute of Physics B