1. Department of Physics Clarendon Laboratory University of Oxford Oxford OX1 3PU UK
2. School of Physical Science and Technology ShanghaiTech University Shanghai 201210 China
3. ShanghaiTech Laboratory for Topological Physics ShanghaiTech University Shanghai 201210 China
4. Diamond Light Source Harwell Science and Innovation Campus Didcot Oxfordshire OX11 0DE UK