Quantum interference in ring-structured molecular junctions: Effects of electron–phonon coupling and lattice dynamics

We investigate the quantum interference (QI) effects in molecular junctions with ring geometry, focusing on the role of electron-phonon (e-ph) coupling and lattice dynamics, using the extended Su-Schrieffer-Heeger model combined with the hierarchical equations of motion approach. In an ideal uniform lattice without e-ph coupling, the current exhibits a clear even-odd dependence on the atom number difference Δ between the two branches, with constructive quantum interference (CQI) for even Δ/2 and destructive quantum interference (DQI) for odd Δ/2. Under frozen-lattice conditions, slight lattice reconstruction induced by the e-ph coupling weakens both CQI and DQI by modifying the phase accumulation along the transport pathways. In contrast, dynamical lattice evolution leads to a pronounced suppression of DQI by continuously disrupting the phase relation between interfering pathways. Moreover, lattice dynamics facilitate the formation of excitonic states, providing additional assisted transport channels and enhancing the current in both CQI and DQI regimes. Our results demonstrate that QI in molecular junctions is governed not only by pathway geometry but also by e-ph coupling and lattice dynamics, highlighting the crucial role of vibronic effects in nanoscale transport.