1. Department of Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111 Budapest, Hungary
2. MTA-BME Condensed Matter Research Group, Budapest University of Technology and Economics, Budafoki út 8, H-1111 Budapest, Hungary
3. Nanobiosensorics Group, Institute of Technical Physics and Materials Science, Centre for Energy Research, Konkoly Thege M. u. 29-33, H-1121 Budapest, Hungary
4. Graduate School of Science, Chiba University, Yayoi-cho 1-33,
Inage-ku, Chiba 263-8522, Japan