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 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) 7 × 7 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.