Prediction of new superconducting bilayers heterostructures using quantum confinement and proximity effects

Abstract

A central challenge in nanoscale superconductivity is to understand and exploit the combined action of quantum confinement and proximity effects in experimentally realistic metallic heterostructures. We theoretically investigate superconducting bilayer heterostructures in which these two effects coexist. Using a generalized Eliashberg framework that incorporates both quantum confinement and proximity coupling, we show that their interplay can substantially enhance the superconducting critical temperature. In particular, the theory predicts superconductivity in selected bilayers whose constituent materials are nonsuperconducting or only weakly superconducting in the bulk. These results identify quantum-confined bilayers as a promising route to engineering emergent superconductivity in metallic heterostructures.

Figures (11)

• Figure 1: Schematic illustration of a superconductor/normal-metal multilayer system combining quantum confinement and the superconducting proximity effect. The superconducting layer ($S$) and the normal-metal layer ($N$) have thicknesses $L_S$ and $L_N$, respectively. Quantum confinement arises from the finite thickness of each layer, while interlayer coupling enables the proximity-induced transfer of superconducting correlations across the interface.
• Figure 2: Critical temperature $T_c$ as a function of the single-layer thickness $L_S$ for an $Al/Mg$ superconductor $Al$-normal metal $Mg$ bilayer with equal layer thicknesses ($L_S=L_N$). Full symbols denote numerical solutions of the confinement- and proximity-modified Eliashberg equations.
• Figure 3: Low temperature gaps values in the superconductive $\Delta_S$ (black full squares) and normal (red full circles) $\Delta_N$ layer as a function of the single-layer thickness $L_S$ for an $Al/Mg$ superconductor $Al$-normal metal $Mg$ bilayer with equal layer thicknesses ($L_S=L_N$). Full symbols denote numerical solutions of the confinement- and proximity-modified Eliashberg equations.
• Figure 4: Critical temperature $T_c$ as a function of the single-layer thickness $L_S$ for a Pb/Mg bilayer with equal layer thicknesses ($L_S=L_N$). Full symbols denote numerical solutions of the confinement- and proximity-modified Eliashberg equations.
• Figure 5: Critical temperature $T_c$ as a function of the single-layer thickness $L_S$ for a Pb/Ag bilayer with equal layer thicknesses ($L_S=L_N$). Full symbols denote numerical solutions of the confinement- and proximity-modified Eliashberg equations.