1. Department of Chemistry, The Chinese University of Hong Kong, Hong Kong SAR 999077, China
2. Department of Physics, University of Houston, Houston, TX 77204
3. Texas Center for Superconductivity, University of Houston, Houston, TX 77204
4. College of Physical Science and Technology, Central China Normal University, Wuhan 430079, China
5. Institute for Advanced Materials, Hubei Normal University, Huangshi 435002, China