1. Physics Faculty Belarusian State University; Independence Ave. 4; 220030; Minsk; Belarus
2. Department of Physics and Nanotechnology; Aalborg University; Skernvej 4A; 9220; Aalborg Øst; Denmark
3. Kazan Physical-Technical Institute; Sibirsky Trakt 10/7; 420029; Kazan; Russian Federation
4. Institute for Experimental Condensed Matter Physics; Ruhr-University Bochum; 44780; Bochum; Germany