1. Department of Electrical Engineering and Computer Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
2. Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz, Germany
3. Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
4. Condensed Matter and Materials Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
5. Department of Energy and Materials Engineering, Dongguk University, Seoul 100-715, Republic of Korea
6. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States