PhD Defense: Gediminas Kirsanskas – University of Copenhagen

PhD Defense: Gediminas Kirsanskas

Electron Transport in Quantum Dots and Heat Transport in Molecules

In my thesis defense I will speak about electron and heat transport through quantum dots in the transistor type setup. More concretely, I will present three rather distinct problems: tunneling renormalization of cotunneling spectroscopy, sub-gap states in superconductors due to spinful quantum dots, and usage of π-stacked molecules as phonon insulators but electric conductors. The first problem is dedicated to the examination of the so-called cotunneling spectroscopy of the quantum dots, where in the Coulomb blockade regime simultaneous electron transport happens through the junction by virtual occupation of the excited states of the dot. More specifically, the renormalization effects of such spectroscopy due to higher order tunneling processes are examined by considering energy level shifts using leading order quasi-degenerate perturbation theory. The second problem is devoted to the study of the emergence of sub-gap states in a junction consisting of two superconducting leads coupled to a spinful quantum dot. Lastly, in the third problem I address the question ``How the heat transport due to center of mass vibrational modes can be reduced in a molecular junction, while maintaining electrical conductivity?''. As one of the possible suggestions a molecular design consisting of two large masses coupled to each other and to the leads is considered.

Supervisors: Karsten Flensberg and Jens Paaske