Structure determination of the Si(111)−7×3−In atomic-layer superconductor

Abstract

The atomic structure of a superconducting atomic sheet of indium grown on Si(111) surface, i.e., $\mathrm{In}/\mathrm{Si}(111)\text{\ensuremath{-}}\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$, is determined by using surface x-ray diffraction (SXRD) and low-energy electron diffraction (LEED). The structure consists of double layers of In atoms with a rectangular arrangement, verifying a theoretical prediction [J. W. Park and M. H. Kang, Phys. Rev. Lett. 109, 166102 (2012)]. For the so-called hexagonal phase, which has been considered to be a different $\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ structure and to undergo a transition to the $\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}$ structure below 265 K, LEED data indicate that the structural basis is $\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}$ even at room temperature. The SXRD data are well reproduced by single-layer In with the In coverage of 10/7 In atoms per Si surface atom, proposed by a theory [J. W. Park and M. H. Kang, Phys. Rev. Lett. 117, 116102 (2016)].