Charge-memory effect in a polaron model: equation-of-motion method for Green functions

We analyze a single-level quantum system placed between metallic leads and strongly coupled to a localized vibrational mode, which models a singlemolecule junction or an STM setup. We consider a polaron model describing the interaction between electronic and vibronic degrees of freedom and develop and examine different truncation schemes in the equation-of-motion method within the framework of non-equilibrium Green functions. We show that upon applying gate or bias voltage, it is possible to observe charge-bistability and hysteretic behavior which can be the basis of a charge-memory element. We further perform a systematic analysis of the bistability behaviour of the system for different internal parameters such as the electron-vibron and the lead-molecule coupling strength.Comment: 12 pages, 5 figure

Green function techniques in the treatment of quantum transport at the molecular scale

The theoretical investigation of charge (and spin) transport at nanometer length scales requires the use of advanced and powerful techniques able to deal with the dynamical properties of the relevant physical systems, to explicitly include out-of-equilibrium situations typical for electrical/heat transport as well as to take into account interaction effects in a systematic way. Equilibrium Green function techniques and their extension to non-equilibrium situations via the Keldysh formalism build one of the pillars of current state-of-the-art approaches to quantum transport which have been implemented in both model Hamiltonian formulations and first-principle methodologies. We offer a tutorial overview of the applications of Green functions to deal with some fundamental aspects of charge transport at the nanoscale, mainly focusing on applications to model Hamiltonian formulations.Comment: Tutorial review, LaTeX, 129 pages, 41 figures, 300 references, submitted to Springer series "Lecture Notes in Physics