[1] Inst Solid State Phys, Chernogolovka 142432, Moscow Region, Russia
[2] Moscow Inst Phys & Technol, Dolgoprudnyi 141700, Russia
[3] Natl Res Univ Higher Sch Econ, Moscow 101000, Russia
[4] Univ Jyvaskyla, Nanosci Ctr, Dept Phys, Jyvaskyla 40014, Finland
[5] Russian Acad Sci, Inst Phys Microstruct, GSP 105, Nizhnii Novgorod 603950, Russia