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

Abstract

We present a tunnel spectroscopy study of single PbS quantum dots (QDs) as a 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 $8\ifmmode\times\else\texttimes\fi{}$ degeneracy of the electronic levels is lifted by the Coulomb interactions and allows the observation of phonon subbands 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 blockade. From the data, a Huang-Rhys factor in the range $S\ensuremath{\sim}1.7\text{--}2.5$ is obtained. Finally, in the shell-tunneling regime, the optical phonons appear in the inelastic ETS ${d}^{2}I/d{V}^{2}$.