Impact of Fano and Breit-Wigner resonances in the thermoelectric properties of nanoscale junctions

TL;DR

This paper investigates how Fano and Breit-Wigner resonances influence the thermoelectric properties of nanoscale junctions, revealing conditions for significant enhancement of thermopower and efficiency.

Contribution

It provides general expressions for thermoelectric coefficients related to these resonances and demonstrates their impact through simulations of real molecular junctions.

Findings

Thermoelectric properties are highly sensitive to resonance type and proximity to Fermi level.

Resonances near the Fermi level significantly enhance thermopower and figure of merit.

Variability in thermoelectric performance depends on molecular coupling, symmetry, and spin filtering.

Abstract

We show that the thermoelectric properties of nanoscale junctions featuring states near the Fermi level strongly depend on the type of resonance generated by such states, which can be either Fano or Breit-Wigner-like. We give general expressions for the thermoelectric coefficients generated by the two types of resonances and calculate the thermoelectric properties of these systems, which encompass most nanoelectronics junctions. We include simulations of real junctions where metalloporphyrin molecules bridge gold electrodes and prove that for some metallic elements the thermoelectric properties show a large variability. We find that the thermopower and figure of merit are largely enhanced when the resonance gets close to the Fermi level and reach values much higher than typical values found in other nanoscale junctions. The specific value and temperature dependence are determined by a series of factors such as the strength of the coupling between the state and other molecular states, the symmetry of the state, the strength of the coupling between the molecule and the leads and the spin filtering behavior of the junction.