通过量子限制和近邻效应将非超导元素转变为超导体
Turning non-superconducting elements into superconductors by quantum confinement and proximity
AI总结：
研究通过量子限制和近邻效应诱导非超导金属超导性，建立统一框架并计算临界温度与薄膜厚度的关系，发现超导性仅在特定条件下出现。
摘要：
本研究探讨了通过量子限制或与近邻效应结合，是否能将非超导的金属转变为超导体。通过建立一种通用框架，基于扩展的各向同性单带Eliashberg理论，计算了不同金属的临界温度随薄膜厚度的变化。结果表明，只有在特定情况下和极窄的厚度窗口内，超导性才会出现，通常在亚纳米尺度（L≈0.4-0.6nm）。此外，还考虑了超导体/正常金属层状结构，其中量子限制和近邻效应共存，预测即使构成材料在本征状态下是非超导或弱超导体，临界温度也会显著增强。
英文摘要：
Elemental good metals, including noble metals (Cu, Ag, Au) and several $s$-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 ($E_F$, $λ$, $μ^$) acquire explicit thickness dependence. By numerically solving the Eliashberg equations using ab initio or experimentally determined electron-phonon spectral functions $α^2F(Ω)$ and Coulomb pseudopotentials $μ^$, and without adjustable parameters, we compute the critical temperature $T_c$ 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 ($L \sim 0.4-0.6$ 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.
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