Shot Noise in Benzenedithiol Single-molecule Junctions from the Perspective of Coherent Wave Function*

Electron transport is typically incoherent in mesoscopic systems. However, electron transport in single-molecule junctions is coherent. Discrete channels may not be reformed in coherent wave functions due to the lack of wave guides. Therefore, shot noise theory identifies fundamental differences between mesoscopic systems and single-molecule junctions. To understand shot noise in single-molecule junctions from the perspective of coherent transport, we calculate shot noise in a benzenedithiol single-molecule junction in terms of effective single-particle wave functions that are obtained self-consistently within density functional theory in scattering approaches. The theoretical value of shot noise is approximately S≈4.03×10^-26 A²/Hz at V_B=0.01 V at a high conductance state (σ≈0.23 G₀), which is in good agreement with the value obtained from a recent experiment (S≈4.37×10^-26 A²/Hz). Our calculations show that the S-Au bonds form the bottlenecks for the current, where the P_x-y orbital dominates the density of states in the energy window between E_FL and E_FR. This finding implies that the shot noise is roughly carried by a single conduction channel owing to the π-bond formed between the sulfur and gold atom, as suggested by the experiment results.