Self-consistent theory of molecular switching

Abstract

We study the model of a molecular switch comprised of a molecule with a soft vibrational degree of freedom coupled to metallic leads. In the presence of strong electron-ion interaction, different charge states of the molecule correspond to substantially different ionic configurations, which can lead to very slow switching between energetically close configurations ͑Franck-Condon blockade͒. Application of transport voltage, however, can drive the molecule far out of thermal equilibrium and thus dramatically accelerate the switching. The tunneling electrons play the role of a heat bath with an effective temperature dependent on the applied transport voltage. Including the transport-induced "heating" self-consistently, we determine the stationary currentvoltage characteristics of the device and the switching dynamics for symmetric and asymmetric devices. We also study the effects of an extra dissipative environment and demonstrate that it can lead to enhanced nonlinearities in the transport properties of the device and dramatically suppress the switching dynamics.

Bistability in a nonequilibrium quantum system with electron-phonon interactions

“…This is certainly expected for strong nonequilibrium situations (large voltage) and/or high temperature and preliminary results indicate that at higher bias voltages the bistability vanishes. Whether this is also the case for zero temperature and smaller bias voltages, as predicted by approximate methods for a single phonon 4,31 , is an open question. In this respect, we find that the bistability persists even for a finite bias assuming that beyond the cutoff time the memory kernel decays as a power law (t −2 ).…”

Spin vibronics in interacting nonmagnetic molecular nanojunctions

“…Thereby, tunneling processes up to second order in the dot-lead hybridization have been taken into account. For slow phonons (i.e., small phonon frequencies), the adiabatic phonon regime has been addressed 17,18 . Also in this regime, Jovchev et al 19 have performed a scattering state renormalization group study in order to compute the I(V ) characteristics and to determine the spectral function under the condition of thermal equilibrium.…”

Cooling a Vibrational Mode Coupled to a Molecular Single-Electron Transistor

“…The mechanical state for k B Te, Γα ≫hω has been discussed in Ref. [30,41] for the molecular case and in Ref. [42,43,32,44] for the metallic case.…”

“…It is characterized also by a bistability [32,41] the limit of large λ both the occupied and unoccupied states are blocked and thus stationary: the final state of the device depends then on the previous history. In order to study the stationary state we begin by assuming that only the probabilities P n0 and P n1 are significantly different from zero.…”