Why have no manifestations of the excitonic mechanism have been detected in Ginzburg sandwiches?

TL;DR

This paper investigates why excitonic mechanisms are not observed in Ginzburg sandwiches, showing that their effects are negligible for typical system sizes and explaining the absence of experimental detection.

Contribution

It provides an exact calculation of the superconducting transition temperature considering excitonic effects, revealing their insignificance in typical Ginzburg sandwich configurations.

Findings

Exitonic mechanisms are negligible for L>>a

Transition temperature is independent of exciton frequency

Manifestations are practically undetectable in typical systems

Abstract

The Ginzburg sandwich is a superconducting film coated with a dielectric layer containing Bose-type exitations, i.e. exitons. Using spatially inhomogeneous Eliashberg equations in the local interaction limit, an exact result for the superconducting transition temperature of the Ginzburg sandwich has been obtained in the first order in a/L (where a is interatomic distance and L is the film thickness). The result has been found to be independent of the exiton frequency. The exitonic mechanism appears only in the second order in a/L since both partners of the Cooper pair should enter a layer of thickness \sim a in order to interact through exchange of exitons. Numerical estimates indicate that manifestations of the exitonic mechanism are practically undetectable in systems with L>>a. Calculations for a narrow-gap and wide-gap dielectric have been performed and compared to experimental data.