Nonequilibrium Energy Transport in Time-Dependent Driven Systems

Abstract

Heat conduction and electric conduction are two fundamental energy transport phenomena in nature. However, they have never been treated equally, because unlike electrons, the carriers of heat?phonons?are just quantized vibration modes that possess no mass or charge, which makes phonon transport hard to be controlled. Nevertheless, a new discipline?phononics emerges, which is the science and technology of phonons, aimed to manipulate heat flow and render thermal energy to be controlled as flexibly as electronics. To achieve this ultimate goal, various thermal devices, like thermal diode, thermal transistor, thermal memory have been proposed theoretically and partially been realized in experiments.

The control of heat flow in the above mentioned thermal devices is managed mainly by applying a static thermal bias with heat commonly flowing on average from ?hot? to ?cool?. In order to obtain an even more flexible control of heat energy comparable with the richness available for electronics, one may design intriguing phononic devices which utilize temporal modulations as well. More intriguing control of transport emerges when the manipulations are made explicitly time-dependent.

In this thesis, I will talk about the dynamic control of nonequilibrium thermal energy transport by various time-dependent driving.

I will first show that an efficient pumping or shuttling of energy across spatially extended nano-structures can be realized via modulating either one or more thermal bath temperatures, or applying external time-dependent fields, such as mechanical/electric/magnetic forces. This gives rise to a plethora of intriguing phononic phenomena such as a directed shuttling of heat against an external thermal bias, multiple thermal resonances. Three necessary conditions for the emergence of heat current without or even against thermal bias are unraveled.

Then I will show if more than a single parameter is modulated in time, the system response is also affected, apart from its dynamic (phase) response, by the manner the modulation proceeds in parameter space. This in turn yields a geometric phase contribution which affects the overall heat transport in a geometric Berry-phase like manner. I will discuss the geometric-phase effect on time-dependent driven heat transport in both quantum and classic systems in details. Finally, the possible experimental setup of electric circuits to verify the prediction about geometric-phase effects on time-dependent heat transport is discussed as well.

As a conclusion, the dynamic control scheme allows for a most fine-tuned control of the energy transport.