Aharonov-Bohm interference in topological insulator nanoribbons

Topological insulators represent novel phases of quantum matter with an insulating bulk gap and gapless edges or surface states. Barrier exists in studying topological surface states by direct transport measurements, presumably due to the predominance of bulk carriers from crystal defects or thermal excitations. Topological insulator nanoribbons are promising candidate to manifest the surface effects due to larger surface-to-volume ratio than bulk materials. We provide unambiguous transport evidence of topological surface states from magnetoresistance measurements of topological insulator material Bi$_{2}$Se$_{3}$ nanoribbons. Pronounced Aharonov-Bohm magnetoresistance oscillations clearly demonstrate the coherent propagation of two-dimensional electrons around the perimeter of the nanoribbon surface, as expected from the topological nature of the surface states.