Tunable heat pump by modulating the coupling to the leads

TL;DR

This paper investigates how modulating the coupling between two leads in a thermal system affects energy flow, revealing controllable heat transfer directions and conditions for no net energy exchange using nonequilibrium Green's functions.

Contribution

It introduces a method to control heat flow by harmonic modulation of lead coupling, providing exact numerical solutions for energy currents in a time-dependent quantum system.

Findings

Modulating coupling can direct energy into or out of leads.

A specific frequency and temperature combination results in no net energy flow.

Higher modulation frequencies enhance transient effects.

Abstract

We follow the nonequilibrium Green's function formalism to study time-dependent thermal transport in a linear chain system consisting of two semi-infinite leads connected together by a coupling that is harmonically modulated in time. The modulation is driven by an external agent that can absorb and emit energy. We determine the energy current flowing out of the leads exactly by solving numerically the Dyson equation for the contour-ordered Green's function. The amplitude of the modulated coupling is of the same order as the interparticle coupling within each lead. When the leads have the same temperature, our numerical results show that modulating the coupling between the leads may direct energy to either flow into the leads simultaneously or flow out of the leads simultaneously, depending on the values of the driving frequency and temperature. A special combination of values of the driving frequency and temperature exists wherein no net energy flows into or out of the leads, even for long times. When one of the leads is warmer than the other, net energy flows out of the warmer lead. For the cooler lead, however, the direction of the energy current flow depends on the values of the driving frequency and temperature. In addition, we find transient effects to become more pronounced for higher values of the driving frequency.