1. International Joint Research Laboratory of New Energy Materials and Devices of Henan Province School of Physics and Electronics Henan University Kaifeng 475004 P. R. China
2. Department of Physics and Astronomy University of New Hampshire Durham NH 03824 USA
3. Institute for Superconducting & Electronic Materials Australian Institute of Innovative Materials University of Wollongong Innovation Campus, Squires Way North Wollongong NSW 2500 Australia