Superconducting single-atomic-layer Tl-Pb compounds on Ge(111) and Si(111) surfaces

The set of known single-atomic-layer (SAL) superconductors has been limited so far by a few examples, including Si(111)-hex-7×3-In reconstruction, Si(111)-SIC-Pb and -HIC-Pb phases, and Si(111)3×3-(Tl, Pb) compound phase. In the present study where transport properties of SAL compounds of Tl-Pb with different composition ratios on Ge(111) and Si(111) substrates have been studied in situ in ultrahigh vacuum, the list of SAL superconductors has been enlarged by three new members, Ge(111)3×3(Tl, Pb), Ge(111)3×3-(Tl, Pb), and Si(111)4×4-(Tl, Pb) systems which show superconducting transition at the critical temperatures of 2.03 K, 0.83 K and 0.79 K, respectively. Bearing in mind that the atomic arrangements and electronic band structures of these SAL compounds of Tl-Pb have already been established, the obtained data set is believed to constitute a solid basis for the prospective theoretical investigations on the nature of SAL superconductivity. In addition, all the new systems demonstrate a noticeable Rashba-type spin splitting in the metallic surface-state bands and, therefore, they might be promising materials for future superconducting spintronics as well as for basics research of exotic superconductivity.