1. a Department of Electrical and Computer Engineering and Department of Physics , Virginia Commonwealth University , Richmond, VA, 23284-3068, USA
2. b Department of Physics and Applied Physics , Kyung Hee University , Kyung-Ki-Do, 5 Yong-In, 449-701, S. Korea
3. c Samsung Advanced Institute of Technology (SAIT) , 14 Nong-Seo Ri, Youn-In City, Gyung-Gee Do, Republic of Korea