1. B. Verkin Institute for Low Temperature Physics and Engineering, Kharkov 61103, Ukraine
2. Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
3. Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
4. Russian Quantum Center, National University of Science and Technology MISIS, Moscow 119049, Russia