Topological charge density waves at halfinteger filling of a moiré superlattice
Abstract
When a flat band is partially filled with electrons, strong Coulomb interactions between them may lead to the emergence of topological gapped states with quantized Hall conductivity. Such emergent topological states have been found in partially filled Landau levels^{1} and Hofstadter bands^{2,3}; however, in both cases, a large magnetic field is required to produce the underlying flat band. The recent observation of quantum anomalous Hall effects in narrowband moiré materials^{47} has led to the theoretical prediction that such phases could be realized at zero magnetic field^{812}. Here we report the observation of insulators with Chern number C = 1 in the zeromagneticfield limit at halfinteger filling of the moiré superlattice unit cell in twisted monolayerbilayer graphene^{7,1315}. Chern insulators in a halffilled band suggest the spontaneous doubling of the superlattice unit cell^{2,3,16}, and our calculations find a ground state of the topological charge density wave at halffilling of the underlying band. The discovery of these topological phases at fractional superlattice filling enables the further pursuit of zeromagneticfield phases that have fractional statistics that exist either as elementary excitations or bound to lattice dislocations.
 Publication:

Nature Physics
 Pub Date:
 January 2022
 DOI:
 10.1038/s41567021014186
 arXiv:
 arXiv:2104.01178
 Bibcode:
 2022NatPh..18...42P
 Keywords:

 Condensed Matter  Strongly Correlated Electrons;
 Condensed Matter  Mesoscale and Nanoscale Physics
 EPrint:
 13 pages, 12 figures