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 [Formula: see text] 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 the spin-splitting of surface-state bands due to the Rashba effect, the occurrence of which 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)[Formula: see text] system, there are many other ordered atomic-layer metal films on silicon differing by composition, structure, strength of SOC, and spin texture, which provide a promising area for prospective investigations of the WAL effect at the atomic-scale limit when the film thickness is less than the electron wavelength.