Theory of magnetotransport in shaped topological insulator nanowires

TL;DR

This paper demonstrates how shaped topological insulator nanowires can be tuned into various transport regimes using a homogeneous magnetic field, highlighting magnetic confinement effects on Dirac surface carriers.

Contribution

It extends the understanding of magnetotransport in shaped TI nanowires, showing tunability of transport regimes without strict symmetry constraints, unlike uniform cross-section nanowires.

Findings

Shaped TI nanowires exhibit five distinct transport regimes.

Magnetic confinement enables regime switching with homogeneous fields.

Transport regimes include conductance steps, resonant transmission, and Coulomb blockade.

Abstract

We show that shaped topological insulator (TI) nanowires, i.e. such that their cross-section radius varies along the wire length, can be tuned into a number of different transport regimes when immersed in a homogeneous coaxial magnetic field. This is in contrast with widely studied tubular nanowires with constant cross-section, and is due to magnetic confinement of Dirac surface carriers. In flat 2D systems such a confinement requires non-homogeneous magnetic fields, while for shaped nanowires of standard size homogeneous fields of the order of $B\sim\,1$T are sufficient. We put recent work [Kozlovsky et al., Phys. Rev. Lett. 124, 126804 (2020)] into broader context and extend it to deal with axially symmetric wire geometries with arbitrary radial profile. A dumbbell-shaped TI nanowire is used as a paradigmatic example for transport through a constriction and shown to be tunable into five different transport regimes: (i) conductance steps, (ii) resonant transmission, (iii) current suppression, (iv) Coulomb blockade, and (v) transport through a triple quantum dot. Switching between regimes is achieved by modulating the strength of a coaxial magnetic field and does not require strict axial symmetry of the wire cross-section. As such, it should be observable in TI nanowires fabricated with available experimental techniques.