Establishing a comprehensive and quantitative understanding of mechanical instabilities in single-molecule junctions is a prerequisite for possible applications in nanoelectronic devices. Recent experimental and theoretical studies have revealed a variety of different processes triggering mechanical instabilities, including current-induced heating and nonconservative forces, however the underlying mechanisms remain largely elusive. In this contribution, we present a fully quantum mechanical investigation of current-induced bond rupture in molecular junctions, employing the numerically exact hierarchical quantum master equation approach [1]. Based on a generic model for molecular junctions, our systematic study identifies three dissociation mechanisms: (1) ultrafast dissociation induced by population of anti-bonding electronic states, (2) incoherent stepwise vibrational ladder climbing, (3) coherent multilevel vibrational excitations induced by multiple electronic transitions. Considering a broad range of different regimes and processes, comprising weak to strong electronic-vibrational and molecule-lead coupling as well as vibrational relaxation, we analyze the different mechanisms in detail. Furthermore, strategies for improving the stability of molecular junctions are discussed.

Current-induced bond rupture in molecular junctions

ACS Spring Meeting 2021

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