Possibilities for enhanced electron-phonon interactions and high- $T_c$ superconductivity in engineered bimetallic nanostructured superlattices

Abstract

We explore theoretically the properties of engineered bimetallic nanostructured superlattices where an array of nanoclusters of a simple (single band) metal are embedded periodically inside another simple metal with a different work function. The exploration is done using a simplified tight-binding model with Coulomb interactions included, and also density functional theory. Taking arrays of Ag clusters of fixed sizes and configurations (when unrelaxed) embedded periodically in a Au matrix as an example, we show that a significant enhancement of electron-phonon interactions ensues, implying possibilities for high superconductivity. The enhancement stems from a strong coupling, via Coulomb interactions, between the dipolar charge distribution that forms at the Au-Ag interfaces and the breathing and other modes of vibration of the light Ag atoms caged inside the heavier Au matrix. The interface dipoles form because of the interplay between the mismatch of the local potential seen by the conduction electrons localized in Wannier orbitals at the Ag and Au sites (the Ag sites being slightly repulsive relative to the Au sites) and the (long-range) Coulomb repulsion between electrons occupying these Wannier orbitals. We also discuss the DC transport in such systems.