Nanoarchitecture. Toward quantum-size tuning of superconductivity

Quantum confinement is known to affect a nanosized superconductor through quantum-size variations of the electronic density of states. Here, it is demonstrate that there is another quantum-confinement mechanism overlooked in previous studies. In particular, it is found that the electron-electron attraction can be enhanced due to quantum-confinement modifications of electronic wave functions. The superconducting correlations are strengthened by such quantum mechanical effect, which creates a subtle interplay with surface-substrate phonon modifications. The combined effect depends on nanofilm thickness and can be controlled by nanoarchitecture. The calculations are in a reasonable agreement with experiments performed on high-quality aluminum films. These findings shed light on the long-standing problem of the size dependence of the critical temperature in low-dimensional superconductors. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)