Anisotropic quantum transport through a diatomic molecule trapped in a nanojunction

Small molecules trapped in nanojunctions have been serving as toy models for the study of many interesting physical phenomena such as quantum tunneling and tunneling-induced light emission to name a few. In previous works, the resonance width due to coupling with leads has been taken as a constant parameter, independent of the scattering region’s orientation. In this work, we describe the electron hopping between metal electrodes and a diatomic molecule microscopically, explicitly considering the molecule’s orientation in the nanojunction. Using the Keldysh formalism and parameters derived from first principles calculations, we show that the quantum transport through the diatomic molecule is highly anisotropic. The spectral function significantly broadens or sharpens depending on the molecular orientation with respect to the axis of the metal leads, which subsequently affects the current. Further, by taking the rotational average of the tunneling matrix elements, we obtain the rotational-state-dependent quantum transport properties.