# Large enhancement in thermoelectric efficiency of quantum dot junction due to increase of level degeneracy

## TL;DR

This paper theoretically shows that increasing the degeneracy of energy levels in quantum dot junctions significantly boosts thermoelectric efficiency, mainly through enhanced electrical conductance, with potential applications in energy conversion.

## Contribution

It introduces a Green-function theoretical model demonstrating how increased level degeneracy enhances the thermoelectric figure of merit ($ZT$) in quantum dot systems.

## Key findings

- Higher degeneracy increases electrical conductance ($G_e$) and $ZT$.
- Seebeck coefficient ($S$) remains unaffected by degeneracy.
- Double quantum dots also show $ZT$ enhancement with increased degeneracy.

## Abstract

It is theoretically demonstrated that the figure of merit ($ZT$) of quantum dot (QD) junctions can be significantly enhanced when the degree of degeneracy of the energy levels involved in electron transport is increased. The theory is based on the the Green-function approach in the Coulomb blockade regime by including all correlation functions resulting from electron-electron interactions associated with the degenerate levels ($L$). We found that electrical conductance ($G_e$) as well as electron thermal conductance ($\kappa_e$) are highly dependent on the level degeneracy ($L$), whereas the Seebeck coefficient ($S$) is not. Therefore, the large enhancement of $ZT$ is mainly attributed to the increase of $G_e$ when the phonon thermal conductance ($\kappa_{ph}$) dominates the heat transport of QD junction system. In the serially coupled double-QD case, we also obtain a large enhancement of $ZT$ arising from higher $L$. Unlike $G_e$ and $\kappa_e$, $S$ is found almost independent on electron inter-dot hopping strength.