[1] Konkuk Univ, Div Quantum Phases & Devices, Dept Phys, Seoul 143701, South Korea
[2] Sungkyunkwan Univ, Dept Mech Engn, Suwon 440746, South Korea
[3] Sogang Univ, Dept Phys, Seoul 121742, South Korea
[4] Korea Inst Adv Study, Seoul 130722, South Korea
[5] Korea Adv Inst Sci & Technol, Grad Sch Energy Environm Water & Sustainabil, NanoCentury KI, Taejon 305701, South Korea
[6] Univ Calif Berkeley, Lawrence Berkeley Lab, Div Mat Sci, Berkeley, CA 94720 USA