Chiral and helical states in selective-area epitaxial heterostructure

The quasi-1D chiral edge states in a quantum anomalous Hall insulator are dissipationless, while the 2D helical surface states in a topological insulator are insensitive to spin-independent scatterings due to the topological protection. Both serve as essential ingredients for topological electronics. Here, we integrate these states into a single device using selective area epitaxy based on the molecular beam epitaxy technique. The chiral edge state comes from the quantum anomalous Hall insulator Cr:(Bi,Sb)(2)Te-3, while the helical surface state comes from the intrinsic topological insulator (Bi,Sb)(2)Te-3 which only interfaces with a partial edge of the former, forming a selective-area heterostructure. At the heterointerface, the chiral state in Cr:(Bi,Sb)(2)Te-3 is allowed to be scattered into (Bi,Sb)(2)Te-3 so that the incoming current will be redistributed according to the coordination between the chirality and helicity. Our device enables the collaboration between chiral and helical states for low-dissipative transport with tunable current dimension. The quantum anomalous Hall effect is a transport phenomenon that has implications in the search for Majorana fermions and quantum metrology. Here, the authors prepare a quantum anomalous Hall bar composed of a magnetic/non-magnetic topological insulating selective-area heterostructure and observe a modulation of the chiral and helical transports at the interface between the two materials by transport measurements.