1. ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
2. Nanophotonic Systems Laboratory, ETH Zürich, 8092 Zürich, Switzerland
3. Institut für Festkörperphysik, Leibniz Universität Hannover, 30167 Hannover, Germany
4. Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany
5. Photonics Laboratory, ETH Zürich, 8093 Zürich, Switzerland
6. Nanoparticles Trapping Laboratory and Research Unit Modeling Nature (MNat), Universidad de Granada, 18071, Granada, Spain
7. Department of Applied Physics, Universidad de Granada, 18071 Granada, Spain
8. ICREA-Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain