1. Photophysics and OptoElectronics Zernike Institute for Advanced Materials University of Groningen Nijenborgh 4 Groningen AG 9747 The Netherlands
2. Cavendish Laboratory University of Cambridge JJ Thomson Avenue CB30HE Cambridge UK
3. State Key Laboratory of Precision Measurement Technology and Instrument Department of Precision Instrument Tsinghua University Beijing 100084 China
4. Laboratoire National des Champs Magnétiques Intenses UPR 3228, CNRS‐UGA‐UPS‐INSA Toulouse 31400 France
5. Department of Experimental Physics Faculty of Fundamental Problems of Technology Wroclaw University of Science and Technology Wroclaw 50‐370 Poland