1. State Key Laboratory for Mechanical Behavior of Materials Xi'an Jiaotong University Xi'an 710049 P. R. China
2. Faculty of Materials Science Lomonosov Moscow State University Leninskie Gory 1 Moscow 119991 Russia
3. Department of Physics Chalmers University of Technology Göteborg SE‐412 96 Sweden
4. Institute of Arctic Technology Moscow Institute of Physics and Technology 9 Institutskiy per., Dolgoprudny Moscow 141701 Russia