1. Faculty of Materials Science, Shenzhen MSU-BIT University, Shenzhen 518172, China
2. Laboratory of Terahertz Spectroscopy, Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Dolgoprudny 171701, Russia
3. 1. Physikalisches Institut, Universität Stuttgart, Stuttgart 70569, Germany
4. Faculty of Materials Science, Lomonosov Moscow State University, Moscow 119991, Russia
5. Department of Physics, Lomonosov Moscow State University, Moscow 119991, Russia
6. Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK