Kondo effect at ultimate atomic-scale two-dimensional limit: Au/Si(111) 3×3 reconstruction with embedded Cr atoms

Abstract

The occurrence of the Kondo effect in the ultimate two-dimensional (2D) case, when the thickness of the conducting film is reduced down to the atomic-scale limit, was explored taking the Tl-adsorbed Au/Si(111)$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ reconstruction with embedded Cr atoms as a prototype system. The reconstruction is essentially an atomic-layer film, which resides on a semiconductor Si(111) substrate and demonstrates conductivity of a metallic type, at least down to 1.8 K. The tight binding of Cr atoms in the interstitial sites surrounded by six Si atoms prevents them from clustering. The Kondo effect in this system was investigated experimentally using low-temperature scanning tunneling spectroscopy and electronic transport measurements. Both techniques yield a Kondo temperature of $\ensuremath{\sim}70--80\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. A substantial increase of the sample resistivity caused by adding Cr atoms is believed to be a specific feature of the extremely thin metallic films, where small amounts of magnetic impurities can effectively block off the narrow conduction channel.