Blurring the boundaries between topological and non-topological phenomena in dots

TL;DR

This study explores the electronic properties of InAsBi quantum dots, revealing that both topological and trivial dots exhibit similar conductance features, blurring the distinction between topological and non-topological phenomena.

Contribution

It introduces a detailed analysis of InAsBi quantum dots, demonstrating the coexistence of topological and trivial edge states and their impact on conductance, expanding understanding of quantum dot topological properties.

Findings

Both topological and trivial QDs show conductance peaks at 2e^2/h.

Geometrically protected edge-like states exist in trivial QDs.

Conductance features can be similar for topological and non-topological dots.

Abstract

We investigate the electronic and transport properties of topological and trivial InAs$_{1-x}$Bi$_x$ quantum dots (QDs). By considering the rapid band gap change within valence band anticrossing theory for InAs$_{1-x}$Bi$_x$, we predicted that Bi-alloyed quantum wells become $\sim 30$meV gapped 2D topological insulators for well widths $d>6.9$nm $(x = 0.15)$ and obtain the $\boldsymbol{k.p}$ parameters of the corresponding Bernevig-Hughes-Zhang (BHZ) model. We analytically solve this model for cylindrical confinement via modified Bessel functions. For non-topological dots we find "geometrically protected" discrete helical edge-like states, i.e., Kramers pairs with spin-angular-momentum locking, in stark contrast with ordinary InAs QDs. For a conduction window with four edge states, we find that the two-terminal conductance ${\cal G}$ vs. the QD radius $R$ and the gate $V_g$ controlling its levels shows a double peak at $2e^2/h$ for both topological and trivial QDs. In contrast, when bulk and edge-state Kramers pairs coexist and are degenerate, a single-peak resonance emerges. Our results blur the boundaries between topological and non-topological phenomena for conductance measurements in small systems such as QDs. Bi-based BHZ QDs should also prove important as hosts to edge spin qubits.