Efficiency fluctuations in quantum thermoelectric devices

TL;DR

This paper introduces a novel method to analyze efficiency fluctuations in nanoscale thermoelectric devices, incorporating quantum effects and nonequilibrium conditions using NEGF and FCS, with practical implications for experimental measurements.

Contribution

It develops a comprehensive NEGF-based framework to quantify efficiency fluctuations, including a Gaussian approximation for experimental accessibility, advancing understanding of quantum thermoelectric performance.

Findings

Efficiency fluctuations are significantly influenced by quantum effects.

The proposed Gaussian method accurately estimates efficiency fluctuations from measurable currents and noises.

Discrepancies between NEGF and QME highlight the quantum nature of fluctuations.

Abstract

We present a method, based on characterizing efficiency fluctuations, to asses the performance of nanoscale thermoelectric junctions. This method accounts for effects typically arising in small junctions, namely, stochasticity in the junction's performance, quantum effects, and nonequilibrium features preventing a linear response analysis. It is based on a nonequilibrium Green's function (NEGF) approach, which we use to derive the full counting statistics (FCS) for heat and work, and which in turn allows us to calculate the statistical properties of efficiency fluctuations. We simulate the latter for a variety of simple models where our method is exact. By analyzing the discrepancies with the semi-classical prediction of a quantum master equation (QME) approach, we emphasize the quantum nature of efficiency fluctuations for realistic junction parameters. We finally propose an approximate Gaussian method to express efficiency fluctuations in terms of nonequilibrium currents and noises which are experimentally measurable in molecular junctions.