Turning non-superconducting elements into superconductors by quantum confinement and proximity.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Bulk elemental metals (Cu, Ag, Au, s-block) typically lack superconductivity due to weak electron-phonon coupling and Coulomb repulsion.
• Quantum confinement in ultra-thin films significantly alters electronic properties and density of states, influencing critical temperature (Tc).

Purpose of the Study:

• To investigate if quantum confinement alone or with proximity effects can induce superconductivity in non-superconducting bulk metals.
• To develop a theoretical framework for predicting superconductivity in confined metals based on Eliashberg theory.

Main Methods:

• Utilized a confinement-generalized, isotropic one-band Eliashberg theory.
• Incorporated energy-dependent normal density of states (DOS) and thickness-dependent material parameters (EF, λ, μ*).
• Numerically solved Eliashberg equations using ab-initio or experimental electron-phonon spectral functions (α2F(Ω)) and Coulomb pseudopotentials (μ*).

Main Results:

• Superconductivity is predicted to emerge in specific metals within extremely narrow thickness windows (∼0.4-0.6 nm).
• Fine-tuning of film thickness is crucial for confinement-induced superconductivity in good metals.
• Layered superconductor/normal-metal heterostructures show predicted substantial enhancement of Tc, even with non-superconducting constituents.

Conclusions:

• Quantum confinement offers a pathway to induce superconductivity in otherwise non-superconducting elemental metals.
• The developed theoretical framework provides a quantitative tool for predicting and designing superconducting thin films.
• Heterostructures combining quantum confinement and proximity effects hold significant promise for achieving enhanced superconducting properties.