We derive and employ a semiclassical Langevin equation obtained from path integrals to describe the ionic dynamics of a molecular junction in the presence of electrical current. The electronic environment serves as an effective nonequilibrium bath. The bath results in random forces describing Joule heating, current-induced forces including the nonconservative wind force, dissipative frictional forces, and an effective Lorentz-type force due to the Berry phase of the nonequilibrium electrons. Using a generic two-level molecular model, we highlight the importance of both current-induced forces and Joule heating for the stability of the system. We compare the impact of the different forces, and the wide-band approximation for the electronic structure on our result. We examine the current-induced instabilities (excitation of runaway "waterwheel" modes) and investigate the signature of these in the Raman signals.
Bibliographical note©2012 American Physical Society
- Electron-Tunneling Spectroscopy
- Molecular-Transport Junctions
- Current-Induced Forces
- Gold Atoms
Lu, J. T., Brandbyge, M., Hedegard, P., Todorov, T. N., & Dundas, D. (2012). Current-induced atomic dynamics, instabilities, and Raman signals: Quasiclassical Langevin equation approach. Physical Review B Condensed Matter, 85(24), Paper 245444. https://doi.org/10.1103/PhysRevB.85.245444