1. Department of Physics, Colorado School of Mines, Golden, Colorado 80401, United States
2. Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław 50-422, Poland
3. Materials Department, University of California, Santa Barbara, California 93106, United States
4. Instituto de Física Teórica, São Paulo State University (UNESP), São Paulo, São Paulo 01049-010, Brazil
5. Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Wrocław 50-422, Poland
6. Department of Mechanical Science and Engineering, University of Illinois Urbana−Champaign, Champaign, Illinois 61820, United States