Weak antilocalization at the atomic-scale limit of metal film thickness.

Creation of the 2D metallic layers with the thickness as small as a few atomic layers and investigation of their properties are interesting and challenging tasks of the modern condensed-matter physics. One of the possible ways to grow such layers resides in the synthesis of the so-called metal-induced reconstructions on silicon (i.e., silicon substrates covered with ordered metal films of monolayer or submonolayer thickness). The 2D Au-Tl compound on Si(111) surface having √7×√7 periodicity belongs to the family of the reconstructions incorporating heavy-metal atoms with a strong spin-orbit coupling (SOC). In such systems, strong SOC results in in the spin-splitting of surface-state bands due to the Rashba effect which occurrence was experimentally proved. Another remarkable consequence of a strong SOC that manifests itself in the transport properties is a weak antilocalization (WAL) effect which has never been explored in the metal layers of atomic thickness. In the present study, the transport and magnetotransport properties of the 2D Au-Tl compound on Si(111) surface were investigated at low temperatures down to ∼2.0 K. The compound was proved to show behavior of the 2D nearly-free electron gas system with metallic conduction as indicated by Ioffe-Regel criterion. It demonstrates the WAL effect which is interpreted in the framework of Hikami-Larkin-Nagaoka theory and possible mechanisms of the electron decoherence are discussed. Bearing in mind that besides the (Au, Tl)/Si(111)√7×√7 system there are a lot of other ordered atomic-layer metal films on silicon differing by composition, structure, strength of SOC and spin texture, they provide a promising playground for prospective investigations of the WAL effect at the atomic-scale limit when the film thickness is less than the electron wavelength.