作者机构:[1]School of Physics and Microelectronics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
相关基金:Project supported by the National Key Basic Research and Development Programme of China (Grant No 2001CB610504) and the National Natural Science Foundation of China (Grant Nos 60576039 and 10374060).Acknowledgments We thank Dr Wang Zhuo and Dr Yang ChangHong for their assistance in the experiment.