Turning non-superconducting elements into superconductors by quantum confinement and proximity
arXiv:2602.07585 · doi:10.1088/1361-648X/ae5907
Abstract
Elemental good metals, including noble metals (Cu, Ag, Au) and several -block elements, do not exhibit superconductivity in bulk at ambient pressure, mainly due to weak electron-phonon coupling that cannot overcome Coulomb repulsion. Quantum confinement in ultra-thin films reshapes the electronic spectrum and the density of states near the Fermi level, producing strong, often non-monotonic, thickness dependencies of the critical temperature in established superconductors. Here, we examine whether confinement alone, or combined with proximity effects, can induce superconductivity in metals that are non-superconducting in bulk form. We review recent theoretical progress and introduce a unified framework based on a confinement-generalized, isotropic one-band Eliashberg theory, where the normal density of states becomes energy dependent and key parameters (, , $μ^$) acquire explicit thickness dependence. By numerically solving the Eliashberg equations using ab initio or experimentally determined electron-phonon spectral functions and Coulomb pseudopotentials $μ^$, and without adjustable parameters, we compute the critical temperature as a function of film thickness for representative noble, alkali, and alkaline-earth metals. The results predict that superconductivity emerges only in selected cases and within extremely narrow thickness windows, typically at sub-nanometer scales ( nm), indicating strong fine-tuning requirements for confinement-induced superconductivity in good metals. We also consider layered superconductor/normal-metal systems where confinement and proximity effects coexist. In these heterostructures, a substantial enhancement of the critical temperature is predicted, even when the constituent materials are non-superconducting or weak superconductors in bulk form.
Topical review
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