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Observation of fractional Chern insulators in a van der Waals heterostructure

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Science  01 Mar 2018:
eaan8458
DOI: 10.1126/science.aan8458

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Abstract

Topologically ordered phases are characterized by long-range quantum entanglement and fractional statistics rather than by symmetry breaking. First observed in a fractionally filled continuum Landau level, topological order has since been proposed to arise more generally at fractional fillings of topologically non-trivial “Chern” bands. Here, we report the observation of gapped states at fractional fillings of Harper-Hofstadter bands arising from the interplay of a magnetic field and a superlattice potential in a bilayer graphene/hexagonal boron nitride heterostructure. We observe phases at fractional filling of bands with Chern indices Embedded Image. Some of these, in Embedded Image and Embedded Image bands, are characterized by fractional Hall conductance—they are “fractional Chern insulators” and constitute an example of topological order beyond Landau levels.

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