Negative Electronic Friction and Non-Markovianity in Nonequilibrium Systems

TL;DR

This paper explores how negative electronic friction in nonequilibrium molecular systems is linked to non-Markovian effects, affecting vibrational dynamics and stability, with validation from quantum simulations.

Contribution

It reveals the generic connection between negative electronic friction and non-Markovian contributions in nonequilibrium vibrational dynamics, supported by numerical simulations.

Findings

Negative electronic friction can drive vibrational modes beyond Joule heating.

Non-Markovian effects significantly influence the dynamics and stability of the system.

Quantum hierarchical equations of motion confirm the importance of non-Markovian contributions.

Abstract

We address the connection between negative electronic friction and non-Markovian effects in the nonadiabatic vibrational dynamics of molecules interacting with metal surfaces under nonequilibrium conditions. We show that a generic nonequilibrium mechanism leading to negative Markovian electronic friction, where molecular vibrations couple directly to inelastic electronic transitions, also introduces significant non-Markovian contributions to the electronic friction. To demonstrate these ideas, we investigate nonequilibrium charge transport through a molecular nanojunction containing a vibrationally coupled donor-acceptor model, where negative electronic friction reflects driving of the vibrational mode beyond standard Joule heating. By comparison to numerically exact, fully quantum hierarchical equations of motion simulations, we verify that these non-Markovian effects have a significant impact on the nonequilibrium dynamics and even on the stability of the resulting Langevin equation.