Quantum mirages in scanning tunneling spectroscopy of Kondo adsorbates: Vibrational signatures

Scanning tunneling microscopy/spectroscopy on Kondo systems consisting of magnetic atoms adsorbed upon nonmagnetic metal surfaces has demonstrated the ability of suitable two-dimensional nanostructures (such as “quantum corrals”) to influence the surface electron transport that is part of the total scanning tunneling microscopy (STM) process. In a well known paradigm, an elliptical arrangement of Co atoms adsorbed on Cu(111) gives rise to an apparent enhanced electronic communication between points on the surface which are near the two elliptical foci. The question addressed here is whether a similar imaging/mirage effect has the potential for being interesting and/or useful when “focused” tunneling processes also involve the vibrational modes of the Kondo adsorbate. Theory for the total process of tip-to-corral-state tunneling, focus-to-focus transport via (corral) surface states [following Agam and Schiller Phys. Rev. Lett. 86, 484 (2001)], and adsorbate resonance scattering has been developed within a localized polaron framework for incorporation of vibrational effects. Calculated lineshapes illustrate the potential utility of tunneling spectroscopy for obtaining detailed, atomic scale understanding of the role of the elliptical nanostructure size, shape, and chemical composition (as manifest in resonance characteristics) on both surface transport processes and also on the measurement methodologies required to probe such systems. This presents unusual challenges since all the characteristic energies (resonance position and width, vibrational, relaxation, and quantum corral) are likely to be of comparable magnitude in realistic experimental STM Kondo systems.