Nonequilibrium molecular vibrons: An approach based on the nonequilibrium Green function technique and the self-consistent Born approximation

We consider the nonequilibrium quantum vibrations of a molecule clamped between two macroscopic leads in a current-carrying state at finite voltages. Our approach is based on the nonequilibrium Green function technique and the self-consistent Born approximation. Kinetic equations for the average populations of electrons and vibrons are formulated in the weak electron-vibron coupling case and self-consistent solutions are obtained. The effects of vibron emission and vibronic instability are demonstrated using few-orbital models. The importance of the electron-vibron resonance is shown.

Figure 1

(Color online) Schematic picture of the considered system.

Figure 2

(Color online) Vibronic emission in the symmetric multilevel model; voltage-current curve, differential conductance, and the number of excited vibrons in the off-resonant (triangles) and resonant (crosses) cases (for details, see the text).

Figure 3

(Color online) Vibronic instability in an asymmetric multilevel model; voltage-current curve, differential conductance, and the number of excited vibrons (crosses). The dashed line shows the voltage-current curve without vibrons (for details, see the text).

Figure 4

(Color online) Floating level resonance; voltage-current curve and the number of excited vibrons (crosses). The dashed line shows the voltage-current curve without vibrons (for details, see the text).