1. Department of Physics, Sungkyunkwan University, Suwon 16419, Korea
2. Center for Neuromorphic Engineering, Korea Institute of Science and Technology, Seoul 02792, Korea
3. Department of Physics, Pusan National University, Busan 46241, Korea
4. Department of Physics and Photon Science, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Korea
5. Department of Energy Science, Sungkyunkwan University, Suwon 16419, Korea
6. Graduate School of Semiconductor Materials and Devices Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919, Korea
7. Department of Physics, Jeonbuk National University, Jeonju 54896, Korea
8. cCPM, Max Planck POSTECH/Korea Research Initiative, Pohang 37673, Korea