Chiral Charge Distribution near Domain Boundary in Twisted Bilayer Graphene Aligned with hexagonal Boron Nitride

Magic-angle twisted bilayer graphene (MATBG) hosts low energy flat bands leading to

interaction-driven instabilities as the Fermi energy are swept through the band. Breaking

the sublattice symmetry by aligning the MATBG with hexagonal Boron Nitride (hBN),

endows the bands with a non-trivial Berry curvature, leading to the emergence of orbital

magnetism near filling of +3 (3 electrons per moire cell). Using scanning tunneling

microscopy and spectroscopy (STM/STS) on this system, we observe multiple domains

where the hBN and MATBG lattices are perfectly aligned despite their lattice mismatch.

The competition between the van der Waals energy gain from alignment and the energy

cost of strain accumulation, leads to 1D domain boundaries (DB) where the alignment is

disrupted. STS maps of the domains and DBs around filling +3 reveal a charge

redistribution that depends on doping, on magnetic field, and displays strong hysteresis.

The DOS maps and associated charge distribution map reveal that in the presence of a

magnetic field the charge distribution is chiral, and that removing the field preserves the

chirality. Furthermore, reversing the field orientation reverses the chirality. These results

which can be attributed to orbital magnetism of the +3 state, suggest that the DB may host

the 1D chiral states responsible for the anomalous QHE observed in transport.