Ching-Chen YehThi-Hien DoPin-Chi LiaoChia-Hung HsuYi-Hsin TuHsin LinT.-R. ChangSiang-Chi WangYu-Yao GaoYu-Hsun WuChu-Chun WuYu An LaiIvar MartinSheng-Di LinChristos PanagopoulosChi-Te Liang2024-10-092024-10-092023-11-03https://scholars.lib.ntu.edu.tw/handle/123456789/721900We studied the role of reduced dimensionality and disorder in the superconducting properties of wafer-scale aluminum (Al) nanofilms. This new generation of ultrathin films were grown using molecular beam epitaxy and depict normal-state sheet resistance at least 20 times lower than the quantum resistance h/(4e2). Defying general expectations, the superconducting transition temperature of our films increases with decreasing Al film thickness, reaching 2.4 K for a 3.5-nm-thick Al film grown on GaAs: twice that of bulk Al (1.2 K). Surface phonon softening is shown to impact superconductivity in pure ultrathin films, offering a route for materials engineering in two dimensions.journal article10.1103/physrevmaterials.7.114801