1. Research Center for Functional Materials, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan
2. Institute of Particle and Nuclear Studies, and International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (QUP, WPI), High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan
3. Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
4. Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan