Open quantum dot model based on three-dimensional topological insulator nanoribbon*

The visibility of the protected surface states of a three-dimensional topological insulator (TI) in transport experiments is strongly suppressed due to the residual bulk contribution to electronic transport. However, TI nanoribbons (TINR) have proven very effective in enhancing the surface state contribution as has been experimentally evidenced by Aharonov-Bohm oscillations. We propose a TINR geometry that can potentially confine the surface electronic states also in the second direction, along the TINR. In this geometry, in the sub-gap region, we find resonant transmission due to the formation of bound states at certain energies. We theoretically study the resonant electron tunnelling through such a quantum dot (QD) attached to TINR leads as a function of the system parameters within the Landauer-Buttiker formalism. External magnetic and electric field tunability of the quantum dot level structure makes the dot feasible for industrial applications. We also investigate the smooth and sharp interfaces incorporating the effect of spin-connection which plays an important role in the motion of the Dirac particles in curved space. Further, we analyse the effect of the Coulomb blockade on the properties of the TI QD and discuss relevant system parameters that are useful to experimentally realize a QD based on the TINR.