Aharanov-Bohm oscillations and perfectly transmitted mode in amorphous topological insulator nanowires

TL;DR

This study investigates how amorphous topological insulator nanowires maintain Aharanov-Bohm oscillations and perfectly transmitted modes despite structural disorder, revealing their robustness up to moderate amorphicity and a topological phase transition at high disorder.

Contribution

It demonstrates the persistence of perfectly transmitted modes in amorphous nanowires protected by chiral or statistical time-reversal symmetry, extending understanding beyond crystalline cases.

Findings

Perfectly transmitted mode persists at low energies in amorphous nanowires.

Aharanov-Bohm oscillations vanish at high amorphicity, replaced by nonquantized resonant peaks.

Resonances are linked to a topological phase transition to a trivial insulator.

Abstract

Crystalline topological insulator nanowires with a magnetic flux threaded through their cross section display Aharanov-Bohm conductance oscillations. A characteristic of these oscillations is the perfectly transmitted mode present at certain values of the magnetic flux, due to the appearance of an effective time-reversal symmetry combined with the topological origin of the nanowire surface states. In contrast, amorphous nanowires display a varying cross section along the wire axis that breaks the effective time-reversal symmetry. In this work, we use transport calculations to study the stability of the Aharanov-Bohm oscillations and the perfectly transmitted mode in amorphous topological nanowires. We observe that at low energies and up to moderate amorphicity the transport is dominated, as in the crystalline case, by the presence of a perfectly transmitted mode. In an amorphous nanowire the perfectly transmitted mode is protected by chiral symmetry or, in its absence, by a statistical time-reversal symmetry. At high amorphicities the Aharanov-Bohm oscillations disappear and the conductance is dominated by nonquantized resonant peaks. We identify these resonances as bound states and relate their appearance to a topological phase transition that brings the nanowires into a trivial insulating phase.