1. Huygens-Kamerlingh Onnes Laboratory, LION, 2300 RA Leiden, Netherlands
2. Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, Netherlands
3. School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, P. R. China
4. Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands