1. School of Science & Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Information Photonic Technique
2. Xi'an Jiaotong University
3. Xi'an 710049, China
4. Department of Physics
5. University of Arkansas
6. Fayetteville, USA
7. National Laboratory of Solid State Microstructures and Department of Physics
8. Nanjing University