1. Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum MaterialsGuangdong Engineering Technology Research Center of Efficient Green Energy and Environment Protection MaterialsSchool of Physics and Telecommunication EngineeringSouth China Normal University Guangzhou 510006 P.R. China
2. INM - Leibniz Institute for New Materials Campus D2 2 66123 Saarbrücken Germany
3. Department of Materials Science & EngineeringSaarland University Campus D2 2 66123 Saarbrücken Germany