  Topological insulator nanoribbons (TI NRs) provide a useful platform to
explore the phase-coherent quantum electronic transport of topological surface
states, which is crucial for the development of topological quantum devices.
When applied with an axial magnetic field, the TI NR exhibits
magnetoconductance (MC) oscillations with a flux period of h/e, i.e.,
Aharonov-Bohm (AB) oscillations, and h/2e, i.e., Altshuler-Aronov-Spivak (AAS)
oscillations. Herein, we present an extensive study of the AB and AAS
oscillations in Sb doped Bi$_2$Se$_3$ TI NR as a function of the gate voltage,
revealing phase-alternating topological AB oscillations. Moreover, the
ensemble-averaged fast Fourier transform analysis on the Vg dependent MC curves
indicates the suppression of the quantum interference oscillation amplitudes
near the Dirac point, which is attributed to the suppression of the phase
coherence length within the low carrier density region. The weak
antilocalization analysis on the perpendicular MC curves confirms the idea of
the suppressed coherence length near the Dirac point in the TI NR.
