Doubling of the superconducting transition temperature in ultra-clean wafer-scale aluminum nanofilms

• Main Authors: Yeh, Ching-Chen, Do, Thi-Hien, Liao, Pin-Chi, Hsu, Chia-Hung, Tu, Yi-Hsin, Lin, Hsin, Chang, T.-R., Wang, Siang-Chi, Gao, Yu-Yao, Wu, Yu-Hsun, Wu, Chu-Chun, Lai, Yu An, Martin, Ivar, Lin, Sheng-Di, Panagopoulos, Christos, Liang, Chi-Te
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2024
• Subjects: Physics; Aluminum film; Quantum resistance
• Online Access: https://hdl.handle.net/10356/173904
• Institution: Nanyang Technological University

We 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.