Visualizing broken symmetry and topological defects in a quantum Hall ferromagnet

Author:

Liu Xiaomeng1ORCID,Farahi Gelareh1ORCID,Chiu Cheng-Li1ORCID,Papic Zlatko2ORCID,Watanabe Kenji3ORCID,Taniguchi Takashi4ORCID,Zaletel Michael P.5ORCID,Yazdani Ali1ORCID

Affiliation:

1. Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ 08544, USA.

2. School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK.

3. Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.

4. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.

5. Department of Physics, University of California, Berkeley, CA 94720, USA.

Abstract

The interaction between electrons in graphene under high magnetic fields drives the formation of a rich set of quantum Hall ferromagnetic (QHFM) phases with broken spin or valley symmetry. Visualizing atomic-scale electronic wave functions with scanning tunneling spectroscopy (STS), we resolved microscopic signatures of valley ordering in QHFM phases and spectral features of fractional quantum Hall phases of graphene. At charge neutrality, we observed a field-tuned continuous quantum phase transition from a valley-polarized state to an intervalley coherent state, with a Kekulé distortion of its electronic density. Mapping the valley texture extracted from STS measurements of the Kekulé phase, we could visualize valley skyrmion excitations localized near charged defects. Our techniques can be applied to examine valley-ordered phases and their topological excitations in a wide range of materials.

Publisher

American Association for the Advancement of Science (AAAS)

Subject

Multidisciplinary

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