Presence versus absence of charging energies in PbTe quantum dots

TL;DR

This study investigates how the charging energy in PbTe quantum dots varies with size, revealing a transition from no measurable charging energy in larger dots to significant energies in smaller ones, and demonstrates gate tunability between quantum dot and ballistic regimes.

Contribution

It provides the first systematic analysis of size-dependent charging energy in PbTe quantum dots and demonstrates gate control over transport regimes.

Findings

Large PbTe QDs show no measurable charging energy.

Smaller PbTe QDs exhibit increasing charging energies, up to 210 μeV.

Gate tuning can switch PbTe devices between quantum dot and ballistic transport regimes.

Abstract

Charging energy ($E_C$) is essential in quantum dot (QD) devices. Previous studies on PbTe QDs have reported both the presence and absence of $E_C$. To resolve this ambiguity, we vary the QD size, i.e. the cross-sectional area of PbTe nanowires, and track the evolution of $E_C$. For large crosssectional areas ($\sim$ 16000 nm$^2$), the PbTe QDs exhibit no measurable $E_C$, while quantized levels are well resolved. Decreasing this area successively to 5000, 1500, and 500 nm$^2$, $E_C$ becomes finite and increases to 80, 160, and 210 $\mu$eV, respectively. We further demonstrate the strong tunability of local gates, which can tune the PbTe device from the QD regime to the regime of ballistic transport. These results address concerns regarding the large dielectric constant of PbTe and provide key insights in engineering advanced PbTe quantum devices.