  Topological insulator (TI) nanoribbons (NRs) provide a unique platform for
investigating quantum interference oscillations combined with topological
surface states. One-dimensional subbands formed along the perimeter of a TI NR
can be modulated by an axial magnetic field, exhibiting Aharonov-Bohm (AB) and
Altshuler-Aronov-Spivak (AAS) oscillations of magnetoconductance (MC). Using
Sb-doped Bi2Se3 TI NRs, we found that the relative amplitudes of the two
quantum oscillations can be tuned by varying the channel length, exhibiting
crossover from quasi-ballistic to diffusive transport regimes. The AB and AAS
oscillations were discernible even for a 70 micrometer long channel, while only
the AB oscillations were observed for a short channel. Analyses based on
ensemble-averaged fast Fourier transform of MC curves revealed exponential
temperature dependences of the AB and AAS oscillations, from which the
circumferential phase-coherence length and thermal length were obtained. Our
observations indicate that the channel length in a TI NR can be a useful
control knob for tailored quantum interference oscillations, especially for
developing topological hybrid quantum devices.
