1. Department of Physics, University of California at San Diego (UCSD), La Jolla, CA 92093, USA.
2. Metal-Insulator Transition Lab, Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-350, Republic of Korea.
3. School of Electrical and Engineering, Pukyong National University, Busan 608-739, Republic of Korea.
4. Center for Metamaterials and Integrated Plasmonics and Electrical and Computer Engineering Department, Duke University, Post Office Box 90291, Durham, NC 27708, USA.