1. Beijing Key Laboratory of Quantum DevicesKey Laboratory for the Physics and Chemistry of Nanodevices and Department of ElectronicsPeking UniversityBeijing100871China
2. Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of SciencesBeijing100190China
3. State Key Laboratory of Superlattices and MicrostructuresInstitute of SemiconductorsChinese Academy of SciencesP.O. Box 912Beijing100083China