Strong coupling in thermoelectric nanojunctions: a reaction coordinate framework

TL;DR

This paper investigates thermoelectric nanojunctions under strong vibrational coupling using a reaction coordinate approach, revealing complex trade-offs and the importance of non-additive effects on efficiency limits.

Contribution

It introduces a reaction coordinate formalism to analyze thermoelectric performance beyond weak coupling, highlighting non-additivity effects and efficiency bounds.

Findings

Strong coupling affects power, efficiency, and noise trade-offs.

Additive environment models can overestimate efficiency bounds.

Non-additivity is crucial for accurate thermoelectric analysis.

Abstract

We study a model of a thermoelectric nanojunction driven by vibrationally-assisted tunneling. We apply the reaction coordinate formalism to derive a master equation governing its thermoelectric performance beyond the weak electron-vibrational coupling limit. Employing full counting statistics we calculate the current flow, thermopower, associated noise, and efficiency without resorting to the weak vibrational coupling approximation. We demonstrate intricacies of the power-efficiency-precision trade-off at strong coupling, showing that the three cannot be maximised simultaneously in our model. Finally, we emphasise the importance of capturing non-additivity when considering strong coupling and multiple environments, demonstrating that an additive treatment of the environments can violate the upper bound on thermoelectric efficiency imposed by Carnot.