Rules of Connectivity-Dependent Phonon Interference in Molecular Junctions

Controlling nanoscale heat flow is crucial for advanced electronics. Phonons, the primary heat carriers in molecules, exhibit wave-like behavior and can interfere, leading to phonon interference (PI). This study reveals that PI in molecular junctions connected to gold electrodes through different contact points deviates significantly from electron quantum interference (QI). Contrary to QI, <i>meta</i>-connected benzenedithiol (BDT), oligophenylene ethynylene (OPE3), bis(phenylethynyl)naphthalene, and bis(phenylethynyl)anthracene junctions can exhibit higher thermal conductance than <i>para</i>-connected ones. This arises from multiple phonon transmission channels and long-range interatomic interactions, both absent in electronic systems. Single-channel phonon transport shows an inverted interference pattern compared to electrons, while multichannel transport resembles QI. It is also demonstrated that dephasing effects have minimal effects on the PI at this scale. Our work provides key insights into phonon transport and offers design strategies for manipulating thermal conductance in molecular junctions, with implications for thermoelectric devices and nanoscale thermal management.