1. NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza
S. Silvestro 12, I-56127 Pisa, Italy
2. St. Petersburg Academic University, Khlopina 8/3, 194021, and St. Petersburg State University, Ulyanovskaya 3, 198504
St. Petersburg, Russia
3. Ioffe Physical Technical Insitute, Politechnicheskaya 26, 194021 St. Petersburg,
Russia