A Strongly Correlated Quantum-Dot Heat Engine with Optimal Performance: An Non-equilibrium Green's function Approach

Abstract

We present an analytical study of a strongly correlated quantum dot-based thermoelectric particle-exchange heat engine for both finite and infinite on-dot Coulomb interaction. Employing Keldysh's non-equilibrium Green's function formalism for different decoupling schemes in the equation of motion, we have analyzed the thermoelectric properties within the non-linear transport regime. As the simplest mean-field approximation is insufficient for analyzing thermoelectric properties in the Coulomb blockade regime, one needs to employ a higher-order approximation to study strongly correlated QD-based heat engines. Therefore initially, we have used the Hubbard-I approximation to study the quantum dot level position ( d ), thermal gradient (∆T ), and on-dot Coulomb interaction (U ) dependence of the thermoelectric properties. Furthermore, as a natural extension, we have used an approximation beyond Hubbard-I in the infinite-U limit (strong on-dot Coulomb repulsion) to provide additional insight into the operation of a more practical quantum dot heat engine. Within this infinite-U limit, we examine the role of the symmetric dot-reservoir tunneling (Γ) and external serial load resistance (R) in optimizing the performance of the strongly correlated quantum dot heat engine. Our infinite-U results show a good quantitative agreement with recent experimental data for a quantum dot coupled to two metallic reservoirs.