A thesis submitted in partial fulfillment for the degree of Doctor of Philosophy in the Faculty of Physics, Chemistry and Materials Science, Department of Materials Physics.The interaction of radiation with matter at the nanoscale has an inexhaustible range of applications in electronics, biotechnology and medicine. At the nanoscale, the length scale where the classical and quantum worlds meet, quantum effects dominate the light–matter interaction and unique phenomena arise. This work addresses fundamental questions on the overlap of quantum theory, non-equilibrium thermodynamics and material science. As the exact description of these quantum phenomena is not feasible, we discuss how the open quantum system approach can be used to study thermal relaxation and thermo-electric transport at the nanoscale. The basic concepts of thermal relaxation are studied from first principles. As the conditions for relaxation are connected with the non-Markovian nature of the equation of motion, we discuss a time-local stochastic Schrödinger equation. Remarkably, this equation can describe thermal relaxation and transport dynamics correctly. Furthermore, this thesis introduces a thermal transport theory where the temperature field is established by radiation of classical blackbodies. The combination of this theory with the techniques of time-dependent current density functional theory provides an ab initio tool to study thermal transport in manybody systems. This approach is general and can be adapted to describe both electron and phonon dynamics. In this way, combined with the time-dependent current DFT, it provides a unified way to investigate ab initio electrical and thermal transport beyond linear response. The observation of thermo-electric transport in macroscopic bodies does not disturb the system or change the flow of energy. However, when moving towards the nanoscale, measurements may influence the system and has to be considered. We demonstrate that the choice of location of these local measurements provides control of the direction of the energy flow and of the particle currents separately. These results seem to violate the second law of thermodynamics. By treating decoherence as a thermodynamic bath we resolve this contradiction. In order to further advance the applications of light–matter interactions for realisable materials, the electronic and optical properties of 2D layered semiconductors are studied. 2D materials have established their place as candidates for the next generation of opto-electronic devices. Specifically, the electronic and optical properties of TiS3 and In2Se3 are theoretically investigated within DFT and many-body perturbation theory. This work constitutes a first step towards exploiting the
trichalcogenide family in 2D opto-electronical applications, such as chemical sensors, passive optical polarisers, fast photodetectors, and battery technologies.Peer reviewe
