Scanning tunneling microscopic observation of enhanced superconductivity in epitaxial Sn islands grown on SrTiO₃ substrate

Recent experimental and theoretical studies of single-layer FeSe film grown on SrTiO₃ have revealed interface enhanced superconductivity, which opens up a pathway to promote the superconducting transition temperature. Here, to investigate the role of SrTiO₃ substrate in epitaxial superconducting film, we grew a conventional superconductor β-Sn (bulk T_c ∼ 3.72 K) onto SrTiO₃ substrate by molecular beam epitaxy. By employing scanning tunneling microscope and spectroscopic measurements, an enhanced T_c of 8.2 K is found for epitaxial β-Sn islands, deduced by fitting the temperature dependence of the gap values using the BCS formula. The observed interfacial charge injection and enhanced electron-phonon coupling are responsible for this T_c enhancement. Moreover, the critical field of 8.3 T exhibits a tremendous increase due to the suppression of the vortex formation. Therefore, the coexistence of enhanced superconductivity and high critical field of Sn islands demonstrates a feasible and effective route to improve the superconductivity by growing the islands of conventional superconductors on perovskite-type titanium oxide substrates.