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

TL;DR

This paper theoretically investigates engineered bimetallic nano-structured superlattices, revealing enhanced electron-phonon interactions that could lead to high-temperature superconductivity, driven by Coulomb-mediated interface dipoles and vibrational modes.

Contribution

It introduces a simplified tight-binding and DFT approach to show how nano-structured superlattices can significantly enhance electron-phonon coupling, suggesting new pathways for high-$T_c$ superconductivity.

Findings

Enhanced electron-phonon interactions in Ag-Au superlattices.

Strong Coulomb coupling between interface dipoles and vibrational modes.

Potential for high-$T_c$ superconductivity in engineered nanostructures.

Abstract

We explore theoretically the properties of engineered bimetallic nano-structured superlattices where an array of nano-clusters 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, as well as density functional theory. Taking arrays of "Ag" clusters of fixed sizes and configurations (when unrelaxed) embedded periodically in an "Au" matrix as an example, we show that a significant enhancement of electron-phonon interactions ensues, implying possibilities for high-$T_c$ 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 localised 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.