This work is devoted to investigation of tunnelling and switching phenomena arising
in Condensed Matter Physics. In the first part I investigate quantum tunnelling of
a single Abrikosov vortex in a superconducting quantum dot. The escape of a vortex
carrying magnetic flux leads to a switching of a quantum dot to non-magnetic state. Tunnelling of a vortex manifests itself as a spontaneous relaxation of magnetization. I
showed that it is possible to use an instanton technique based on path integral formalism
even in presence of forces breaking time-reversal symmetry. [Continues.]
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy at Loughborough University.
Loughborough University (research studentship). European Physical Society (European Mobility Scheme for Physics Students, EMSPS). Committee of Vice-Chancellors and Principals of the Universities of the United Kingdom (Overseas Research Studentship, ORS). European Science Foundation.