Suppression of scattering in quantum confined 2D-helical Dirac systems

TL;DR

This paper investigates how disorder affects transport in quantum confined 2D-helical Dirac systems, revealing that interface properties dominate conductance and noise characteristics in large mode regimes, with implications for nanowire device design.

Contribution

It demonstrates that in large transverse mode regimes, transport properties are primarily governed by contact interfaces rather than disorder or geometry, providing analytical results for conductance and noise.

Findings

Conductance proportional to energy with average transmission π/4.

Fano factor approximately 0.13 in heavily doped contacts.

Transport insensitive to disorder when many transverse modes are present.

Abstract

Transport properties of disordered quantum confined helical Dirac systems are investigated in the large energy limit. As long as the 2D transport length is larger than the perimeter of the nanowire, the conductance and the Fano factor are sensitive to disorder only when the Fermi energy is close to an opening of a transverse mode. In the limit of a large number of transverse modes, transport properties are insensitive to the geometry of the nanowire or the nature and strength of the disorder but, instead, are dominated by the properties of the interface between the ohmic contact and the nanowire. In the case of a heavily doped Dirac metallic contact, the conductance is proportional to the energy with an average transmission $\mathcal{T}=\pi/4$ and a Fano factor of $F\simeq 0.13$. Those results can be generalized to a much broader class of contacts, the exact values of $\mathcal{T}$ and $F$ depending on the model used for the contacts. The energy dependence of Aharonov-Bohm oscillations is determined, when a magnetic flux is threaded through the cross section of the nanowire.