T. Brumme

Dynamical bistability of single-molecule junctions: A combined experimental/theoretical study of PTCDA on Ag(111)

The dynamics of a PTCDA-Ag(111) molecular junction has been investigated experimentally and theoretically. Switching between two conductance states was observed by low-temperature scanning tunneling microscopy, and was dependent on the tip-substrate distance and the applied bias, but was less sensitive to the bias polarity. Using a minimal model Hamiltonian approach combined with density-functional calculations, the switching was shown to be related to the scattering of electrons tunneling through the junction, which progressively excite the relevant chemical bond. Depending on the direction in which the molecule switches, different molecular orbitals are shown to dominate the transport and thus the vibrational heating process. This in turn can dramatically affect the behavior of the switching rate, demonstrating the importance of modelling the DOS realistically.

Vibrational Heating in Single-Molecule Switches

It has been recently shown experimentally that the switching rate in single-molecule junctions sensitively depends on the applied bias voltage. Using a minimal model which describes the barrier crossing problem by multiple excitations of vibrations of the molecular junction and by taking into account the molecule specific nonconstant density of states, we are able to describe the complex, non-monotonic behavior of the switching process.

Vibrational heating in single-molecule switches: an energy-dependent density-of-states approach

In recent experiments, it has been shown that the switching rate of single-molecule switches can show a rather complicated dependence on the applied bias voltage. Here, we discuss a minimal model which describes the switching process in terms of inelastic scattering processes of the tunneling electron by specific molecular vibrations. One important point is the introduction of an energy-dependent electronic density of states around the Fermi energy. The influence of different model parameters on the switching rate is studied and we show that the inclusion of a variable density of states allows us to understand the non-monotonic behavior of the switching rate observed in some experiments.