Charge-vibration interaction effects in normal-superconductor quantum dots

Year: 2017

Authors: Stadler P., Belzig W., Rastelli G.

Autors Affiliation: Univ Konstanz, Fachbereich Phys, D-78457 Constance, Germany. Univ Konstanz, Zukunftskolleg & Fachbereich Phys, D-78457 Constance, Germany.

Abstract: We study the quantum transport and the nonequilibrium vibrational states of a quantum dot embedded between a normal-conducting and a superconducting lead with the charge on the quantum dot linearly coupled to a harmonic oscillator of frequency omega. To the leading order in the charge-vibration interaction, we calculate the current and the nonequilibrium phonon occupation by the Keldsyh Green´s function technique. We analyze the inelastic, vibration-assisted tunneling processes in the regime omega>omega. We also found that inelastic vibration-assisted Andreev reflections as well as quasiparticle tunneling induce a strong nonequilibrium state of the oscillator. In different ranges on the dot´s level, we found that the current produces: ( i) ground-state cooling of the oscillator with phonon occupation n << 1, ( ii) accumulation of energy in the oscillator with n >> 1, and ( iii) a mechanical instability characterized by a negative damping coefficient. We show that ground-state cooling is achieved simultaneously for several modes of different frequencies. Finally, we discuss how the nonequilibrium vibrational state can be readily detected by the asymmetric behavior of the inelastic current peaks with respect to the gate voltage.


Volume: 96 (4)      Pages from: 045429  to: 045429

More Information: We acknowledge J. C. Cuevas, E. Scheer, S. Andergassen, and T. Pietsch for interesting discussions and useful comments. This research was supported by the Zukunftskolleg of the University of Konstanz and by the DFG through the collaborative research center SFB 767.
KeyWords: quantum dots, quantum electromechanical systems, Andreev states
DOI: 10.1103/PhysRevB.96.045429