Superconductivity in a two monolayer thick indium film on Si(111) 3×3 -B

Two-monolayer-thick In film with a $\ensuremath{\surd}7\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}3$-rect structure is known to show superconductivity at 3.18 K on the $\mathrm{Si}(111)7\ifmmode\times\else\texttimes\fi{}7$ substrate. We synthesized the $\ensuremath{\surd}7\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}3$-In-rect film on the $\mathrm{Si}(111)\ensuremath{\surd}3\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}3\text{\ensuremath{-}}\mathrm{B}$ substrate and found that it also became a superconductor at ${T}_{c}$ = 2.38 K. The In film on the $\ensuremath{\surd}3\text{\ensuremath{-}}\mathrm{B}$ substrate showed the two-dimensional free-electron-like circular Fermi surface as on the $7\ifmmode\times\else\texttimes\fi{}7$ substrate. However, the butterfly-wing-like shape contour at the Fermi surface was found to be shifted and enlarged on the $\ensuremath{\surd}3\text{\ensuremath{-}}\mathrm{B}$ substrate. Density functional calculations revealed that it was caused by the difference of the substrate. ${T}_{c}$ on the $\ensuremath{\surd}3\text{\ensuremath{-}}\mathrm{B}$ substrate was considered to be identical to that on the $7\ifmmode\times\else\texttimes\fi{}7$ substrate in consideration of the recently reported surface defect density dependence of ${T}_{c}$. These results indicated that the interaction with the substrate does not play a crucial role in the superconductivity of the two-monolayer-thick In film.