Effects of electron-phonon interactions on the electron tunneling spectrum of PbS quantum dots

TL;DR

This study investigates how strong electron-phonon interactions influence the electron tunneling spectrum of PbS quantum dots, revealing phonon sub-bands, Franck-Condon blockade, and quantifying the Huang-Rhys factor.

Contribution

It provides the first detailed tunneling spectroscopy analysis of electron-phonon coupling effects in PbS quantum dots, including phonon sub-bands and Franck-Condon blockade.

Findings

Observation of phonon sub-bands due to optical phonons

Identification of Franck-Condon blockade in ETS

Quantification of Huang-Rhys factor between 1.7 and 2.5

Abstract

We present a tunnel spectroscopy study of single PbS Quantum Dots (QDs) as function of temperature and gate voltage. Three distinct signatures of strong electron-phonon coupling are observed in the Electron Tunneling Spectrum (ETS) of these QDs. In the shell-filling regime, the $8\times$ degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon sub-bands that result from the emission of optical phonons. At low bias, a gap is observed in the ETS that cannot be closed with the gate voltage, which is a distinguishing feature of the Franck-Condon (FC) blockade. From the data, a Huang-Rhys factor in the range $S\sim 1.7 - 2.5$ is obtained. Finally, in the shell tunneling regime, the optical phonons appear in the inelastic ETS $d^2I/dV^2$.