Chern junctions in Moiré-Patterned Graphene/PbI2

Abstract

Expanding the moire material library continues to unlock novel quantum phases and emergent electronic behaviors. Here, we introduce PbI2 into the moire family and investigate the magnetotransport properties of moire superlattice in a hexagonal boron nitride/graphene/PbI2 heterostructures. In the high-field quantum Hall regime, we observe robust dissipationless transport at the charge neutrality point, indicative of incompressible states at filling factor vh = 0. Additionally, a fractional conductance plateau at 2/3 e2/h emerges, which we attribute to a Chern junction between domains with distinct Chern numbers originating from moire-modulated and conventional integer quantum Hall states. The moire Hofstadter spectrum displays an unconventional flavor sequence, likely influenced by proximity-induced spin-orbit coupling from the PbI2 layer. We also see coherent electronic interference along lines with Chern number vm = -2. These observations provide compelling evidence for the formation of moire domains that nontrivially interrupt incompressible quantum Hall states, reflecting the strong moire potential in the BN/graphene/PbI2 superlattice. We suggest that the moire Hofstadter spectrum coupled with the proximity-induced spin-orbit interaction from PbI2 gives rise to a high magnetic field topological insulator phase explaining ballistic transport at the charge neutrality point in the graphene monolayer.