1. Departament de Física, Universitat Jaume I, Av. Sos Baynat, s/n, 12071 Castelló, Spain, Hahn-Meitner-Institute Glienicker Strasse 100, 14109 Berlin, Germany, and Photonics and Optoelectronics Group, Physics Department and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität München, Amalienstrasse 54, 80799 Munich, Germany