STM and laser-driven atom switch: An open-system density-matrix study of H/Si(100)

A recently proposed single atom switch, experimentally realized with a scanning tunneling microscope (STM) for H on a Si(100) surface [U.J. Quaade et al., Surf. Sci. 415, L1037 (1998)], is examined here theoretically. Using a two-state model and open-system density matrix theory which includes both electronic and vibrational relaxation of the adsorbate, we argue that the switching is dominated by tunneling in the ground state. The model accounts for observed isotope and, qualitatively, for temperature effects. We suggest that also a laser-driven H switch should be possible.