1. School of Civil Engineering, Wuhan University, Wuhan, 430072, China
2. Department of Materials Science & Engineering, and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, USA
3. Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA
4. Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic