1. Department of Energy Science (DOES) and Center for Artificial Atoms, Sungkyunkwan University, Suwon 16419, Republic of Korea
2. Department of Physics, Hanyang University, Seoul 04763, Republic of Korea
3. SKKU Institute of Energy Science and Technology (SIEST), Sungkyunkwan University, Suwon 16419, Republic of Korea
4. Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States