1. Institute for Technical Physics and Materials Science, Centre for Energy Research, Hungarian Academy of Sciences, Konkoly Thege M. út 29-33, H-1121 Budapest, Hungary
2. Wigner Research Centre for Physics, Hungarian Academy of Sciences, Konkoly-Thege M. út 29-33, H-1121 Budapest, Hungary
3. Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia