1. Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, 80539 München, Germany
2. The Barcelona Institute of Science and Technology, ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Spain
3. National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan