1. Department of Physics, University of Oslo, P.O. Box 1048 Blindern, Oslo 0316, Norway and Norwegian Defense Research Establishment (FFI), Kjeller, Norway
2. Department of Physics, University of Oslo, P.O. Box 1048 Blindern, Oslo 0316, Norway and Institute for Superconducting and Electronic Materials, University of Wollongong Northfields Ave., Wollongong, NSW 2522, Australia
3. Department of Physics, University of Oslo, P.O. Box 1048 Blindern, Oslo 0316, Norway and Ioffe Physical Technical Institute, 26 Polytekhnicheskaya, St Petersburg 194021, Russia