1. Technische Universität Darmstadt, Eduard-Zintl-Institut, Alarich-Weiss-Straße 8, 64287 Darmstadt, Germany
2. Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria
3. School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom