1. Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
2. Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546
3. Laboratorio TASC, IOM-CNR, S.S. 14 km 163.5, Basovizza, 34149 Trieste, Italy
4. Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE, United Kingdom