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 C=–1, ±2, and ±3. Some of these, in C=–1 and C=2 bands, are characterized by fractional Hall conductance—they are “fractional Chern insulators” and constitute an example of topological order beyond Landau levels.
Published in: "Science (Advanced Online Publication)".