Enhancement of Ising Superconductivity in Pb_1-xBi_x Ultrathin Films

Ising superconductivity has garnered much attention in recent years due to its extremely high in-plane upper critical field (B_\rm c2). Here, we fabricated 14 multilayer Pb_1-xBi_x (0%\le x\le 40%) thin films on Si (111)-7\times 7 reconstructed surface by molecular beam epitaxy. Large B_\rm c2 beyond the Pauli limit is observed in all the Pb_1-xBi_x films, indicating that they may exhibit characteristics of Ising superconductivity. Moreover, the introduction of Bi doping can significantly enhance and effectively tune the in-plane B_\rm c2 of Pb_1-xBi_x films, which will help us better understand Ising superconductivity and provide a new platform for the development of tunable Ising superconductors.