Electromechanical instability in vibrating quantum dots with effectively negative charging energy

摘要

In quantum dots or molecules with vibrational degrees of freedom theelectron-vibron coupling renormalizes the electronic charging energy. Forsufficiently strong coupling, the renormalized charging energy can becomenegative. Here, we discuss an instability towards adding or removing anarbitrary number of electrons when the magnitude of the renormalized chargingenergy exceeds the single-particle level spacing. We show that the instabilityis regularized by the anharmonic contribution to the vibron energy. Theresulting effective charging energy as a function of the electron number has adouble-well structure causing a variety of novel features in the Coulombblockade properties.