Quantum-coherent Enhancement of Nonlinear Thermoelectricity on Nanoscale Heat Engines

We theoretically investigate how we can improve thermoelectric performance of nanoscale heat engines by controlling quantum coherence, which we can regulate in nanostructures such as by deforming device geometry, making direct channels between environments, or applying gate voltages. We show how one improves both thermal efficiency and output power by taking two realizations: (1) a quantum-dot interferometer (a quantum dot embedded in the ring geometry), where one can analytically evaluate various quantities, and (2) a graphene nano-ribbon junction of double bend or rhombus geometry. In the latter, we also consider the degradation effect due to phonon, but relatively good thermoelectricity perseveres in some parameter regions. We also argue power bounds and how one can predict controllability in the fully nonlinear regime based on linear-response quantities.