期刊
NATURE PHYSICS
卷 14, 期 9, 页码 930-935出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/s41567-018-0190-0
关键词
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资金
- National Science Foundation [DMR-1654186, DMR-1157490]
- Army Research Office [69188PHH]
- David and Lucile Packard Foundation
- Elings Prize Fellowship in Science of the California Nanosystems Institute at the University of California, Santa Barbara (UCSB)
- State of Florida
- Elemental Strategy Initiative
- Japan Society for the Promotion of Science KAKENHI [JP15K21722]
In monolayer graphene, the two inequivalent sublattices of carbon atoms combine with the electron spin to give electrons a nearly fourfold degenerate internal isospin. At high magnetic fields, the isospin degeneracy increases the already large intrinsic degeneracy of the two-dimensional Landau levels, making low-disorder graphene systems a versatile platform for studying multicomponent quantum magnetism. Here, we describe magnetocapacitance experiments of ultraclean monolayer graphene devices in which a hexagonal boron nitride substrate breaks the symmetry between carbon sublattices. We observe a phase transition in the isospin system, which is marked by unusual transitions in odd-denominator fractional quantum Hall states for filling factors nu near charge neutrality and by the unexpected appearance of incompressible even-denominator fractional quantum Hall states at nu = +/- 1/2 and nu = +/- 1/4. We propose a scenario in which the observed states are multicomponent fractional quantum Hall states incorporating correlations between electrons on different carbon sublattices, associated with a quantum Hall analogue of the Neel-to-valence bond solid transition that occurs at charge neutrality.
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