Visualizing and manipulating chiral edge states in a graphene-based quantum anomalous Hall insulator*

Quantum anomalous Hall (QAH) insulators are topological phases of matter that host one-dimensional chiral edge-states that conduct electrical current unidirectionally, thus leading to quantized Hall conductance and dissipationless carrier transport. We have used scanning tunneling microscopy and spectroscopy to directly visualize and manipulate chiral edge states in a moiré QAH insulator made from twisted monolayer-bilayer graphene. We are able to control the local Chern number by manipulating the device carrier concentration, thus stabilizing adjacent domains having opposite Chern number and enabling the visualization of chiral edge states residing at domain interfaces that are independent of structural boundaries within our samples. The use of conventional back-gating to vary the carrier density enables chiral edge-states to be reversibly moved across the unbroken moiré landscape. Formation of tip-induced quantum dots provides more local control over carrier density and Chern number, thus allowing intentional creation of chiral edge states having reversible chirality. This approach to visualizing chiral edge states eliminates the complications of edge defects, dangling bonds, and trivial interface states that have plagued previous measurements.