1. Optical
Nanomaterial Group, Institute for Quantum Electronics, Department of Physics, ETH Zürich, Auguste-Piccard- Hof 1, 8093 Zürich, Switzerland
2. Department
of Nanophotonics and Metamaterials, ITMO University, St. Petersburg 197101, Russia
3. Department
of Physics and Mathematics, University of Eastern Finland, Yliopistokatu
7, 80101, Joensuu, Finland
4. IBM Research−Zurich, Säumerstrasse 4, 8803 Rüschlikon, Switzerland
5. Laboratory
for Interfaces, Soft Matter, and Assembly, Department of Materials, ETH Zürich, Vladimir-Prelog- Weg 5, 8093 Zürich, Switzerland
6. Nonlinear
Physics Center, Australian National University, Canberra, Australian Capital
Territory 2601, Australia