Surface-state–mediated three-adsorbate interaction

¹ Department of Applied Physics, Chalmers University of Technology and Göteborg University - S-412 96 Gothenburg, Sweden
² Department of Physics, University of Maryland, College Park - MD 20742-4111, USA

Received: 31 December 2001
Accepted: 16 April 2002

Abstract

The interaction energy of three adsorbates on a surface consists of the sum of the three pair interactions plus a trio contribution produced by interference of electrons which propagate the entire perimeter, d₁₂₃, of the three-adsorbate cluster. Here we investigate this triple-adsorbate interaction that is mediated by the isotropic Shockley surface-state band found on noble-metal (111) surfaces. Our experimentally testable result depends on the s-wave phase shift, , characterizing the standing-wave patterns seen in scanning-tunneling microscopy (STM) images. Compared with the adsorbate-pair interactions, and in contrast to bulk-mediated interactions, the trio contribution has a slightly weaker amplitude and asymptotically decays slightly faster, . It also has a distinctive oscillation period dependent on d₁₂₃. We finally compare the asymptotic description with exact model calculations.