1. Department of Physics and Nanotechnology, Aalborg University, Skjernvej 4A, DK-9220, Aalborg Øst, Denmark
2. Institute of Sensors, Signals and Electrotechnics (SENSE), University of Southern Denmark, Niels Bohrs Allé 1, DK-5230 Odense M, Denmark
3. ISIS, CNRS et Université de Strasbourg, 8 allée G. Monge - BP 70028, 67083 Strasbourg, Cedex, France