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Time-dependent thermal transport theory

Understanding thermal transport in nanoscale systems presents important challenges to both theory and experiment. In particular, the concept of local temperature at the nanoscale appears difficult to justify. Here, we propose a novel theoretical approach where we replace the temperature gradient with controllable external black-body radiations. The theory recovers known physical results, for example the linear relation between the thermal current and the temperatures difference of two black-bodies. Furthermore, our theory is not limited to the linear regime and goes beyond accounting for non linear effects and transient phenomena. In the strong coupling and large temperature gradients, we show that there is a maximum energy current that the system can sustain and we recover the Kramers' turnover. Since the present theory is general and can be adapted to describe both electron and phonon dynamics, it provides a first step towards a unified formalism for investigating thermal and electronic transport.