[1
]Department of Physics/Centre for Materials Science and Nanotechnology, University
of Oslo, P.O. Box 1048, Blindern, N-0316 Oslo, Norway
[2
]ABB Corporate Research, Segelhofstrasse 1K, 5405 Baden-Dättwil, Switzerland
[3
]Lawrence Livermore National Laboratory, Livermore, California 94550, USA