1. Institute for Quantum Electronics, ETH Zürich, CH-8093 Zürich, Switzerland
2. Center for Emergent Matter Science, RIKEN, Wako, Saitama 351-0198, Japan
3. Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
4. International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan