Topological energy gaps in the [111]-oriented InAs/GaSb and GaSb/InAs core-shell nanowires

TL;DR

This study investigates the topological energy gaps in [111]-oriented InAs/GaSb and GaSb/InAs core-shell nanowires, revealing how structural parameters influence their electronic properties and potential for topological applications.

Contribution

It provides a detailed analysis of how core radius and shell thickness affect the fundamental energy gaps, highlighting the importance of electron-hole state localization for topological features.

Findings

Maximum gap of ~4.4 meV in GaSb/InAs nanowires

Wider gap persistence in GaSb/InAs nanowires

Quantum size effects dominate energy gap evolution

Abstract

The [111]-oriented InAs/GaSb and GaSb/InAs core-shell nanowires have been studied by the $8\times 8$ Luttinger-Kohn $\vec{k}\cdot\vec{p}$ Hamiltonian to search for non-vanishing fundamental gaps between inverted electron and hole bands. We focus on the variations of the topologically nontrivial fundamental gap, the hybridization gap, and the effective gap with the core radius and shell thickness of the nanowires. The evolutions of all the energy gaps with the structural parameters are shown to be dominantly governed by quantum size effects. With a fixed core radius, a topologically nontrivial fundamental gap exists only at intermediate shell thicknesses. The maximum gap is $\sim 4.4$ meV for GaSb/InAs and $\sim 3.5$ meV for InAs/GaSb core-shell nanowires, and for the GaSb/InAs core-shell nanowires the gap persists over a wider range of geometrical parameters. The intrinsic reason for these differences between the two types of nanowires is that in the shell the electron-like states of InAs is more delocalized than the hole-like state of GaSb, while in the core the hole-like state of GaSb is more delocalized than the electron-like state of InAs, and both features favor stronger electron-hole hybridization. Since similar features of the electron- and hole-like states have been found in nanowires of other materials, it could serve as a common rule to put the hole-like state in the core while the electron-like state in the shell of a core-shell nanowire to achieve better topological properties.