Aharonov-Bohm Interference and Phase-Coherent Surface-State Transport in Topological Insulator Rings

We present low-temperature magnetotransport measurementson selectivelygrown Sb2Te3-based topological insulator ringstructures. These devices display clear Aharonov-Bohm oscillationsin the conductance originating from phase-coherent transport aroundthe ring. The temperature dependence of the oscillation amplitudeindicates that the Aharonov-Bohm oscillations originate from ballistictransport along the ring arms. We attribute these oscillations tothe topological surface states. Further insight into the phase coherenceis gained by comparing with similar Aharonov-Bohm-type oscillationsin topological insulator nanoribbons exposed to an axial magneticfield. Here, quasi-ballistic phase-coherent transport is confirmedfor closed-loop topological surface states in the transverse directionenclosing the nanoribbon. In contrast, the appearance of universalconductance fluctuations indicates phase-coherent transport in thediffusive regime, which is attributed to bulk carrier transport. Thus,it appears that even in the presence of diffusive p-type charge carriers in Aharonov-Bohm ring structures, phase-coherentquasi-ballistic transport of topological surface states is maintainedover long distances.