Phonon backaction in diatomic molecular junctions: Negative differential conductance, quantum interference and super-Poissonian noise

We present a study of the non-equilibrium electron transport through diatomic molecular junctions employing the full counting statistics (FCS) in combination with the self-consistent Born approximation (SCBA). Here, we consider two different types of electron-phonon coupling in a molecule. One is the coupling of the molecular vibration to the electrons in each orbital (intra-orbital coupling) and the other is to the transferring electrons (inter-orbital coupling). We show that the super-Poissonian noise is enhanced by increasing the electron-phonon coupling in the presence of the phonon backaction. In the weak coupling regime for the inter-orbital coupling, the negative differential conductance (NDC) can take place in the resonant tunneling regime. It turns out that the current fluctuation suppresses NDC, but induces the quantum interference in molecular conductance.