Exploring two facets of physics: Coherent current transport in superconducting structures. Phenomenographic studies of sense-making in physics

Doktorsavhandling, 2002

This thesis has two major parts. It draws upon and contributes both to the physics and the pedagogical research traditions. It consists of two acts, and a discussion on the relation between the two acts. The main result in the physics part is the development of a coherent MAR (multiple Andreev reflection) theory for SNS junctions. The theory takes into account finite length, multiple modes, arbitrary amount of backscattering and finite temperature. It is based on the coherent MAR scheme using the scattering approach, which was developed for quantum point contacts (ScS). In finite length junctions, the current is considerably enhanced for subgap voltages, compared to short junctions. Resonances through superconducting bound states give subgap structures on the current-voltage characteristics, and the positions of the structures are directly related to the bound state energies and do not coincide with the subharmonic gap structure positions. In finite length junctions the positions of the subgap structures do not scale with the superconductor gap as a function of temperature, as is the case in short junctions. Parts of the results show qualitative agreement with experiments on S-2DEG-S junctions. In the pedagogical part, the results of two phenomenographic studies are reported. They illuminate, on a general level, my object of research "What does it mean to become a physicist?". In particular they include analyses of how students make sense of studying Physics in the first year of study, the ways in which senior students and (condensed matter) physics researchers expound on physics, and how (condensed matter) physics researchers conceptualize the judging of trustworthiness of research results. Additionally, a methodological consideration on the issue of context in phenomenographic research has been made. In the thesis, physics is sketched as a systematic search for intelligibility, which takes place within a social context, in which a particular world view is a common starting point. The researcher and the community are essentially engaged in an enterprise of learning at both the individual and the collective level. The quality of this learning determines the quality of the research results. There is thus a potential for informing and supporting the education of physicists and physics research itself, with the kind of investigations made in this thesis.