1. Central European Institute of Technology - Brno University of Technology (CEITEC BUT), Purkyňova 123, 612 00 Brno, Czech Republic
2. Institute of Physical Engineering, Brno University of Technology, Technická 2, 616 69 Brno, Czech Republic
3. Department of Physics and Materials Engineering, Faculty of Technology, Tomas Bata University in Zlín, Vavrečkova 275, 760 01 Zlín, Czech Republic
4. Solid State Physics Laboratory, ETH Zürich, CH 8093 Zürich, Switzerland