The original version of this Article had a few typesetting errors in the main text. In the section “Results and discussion”, subsection “Propagating collective excitations”, the 4th paragraph, the texts “a less pronounced dependence of intensity on thickness” were mistakenly written as “a less pronounced thickness-dependent intensity”. In the same subsection, the 9th paragraph, the equation “ω2 p ¼ e2 2ε0εr nM meff q1” was mistakenly written as “ω2 p ¼ e2 4ε0εr nM meff q1” and the equation “nM¼ 3 1010cm À2” was mistakenly written as “nM¼ 6 1010cm À2”. These errors have been corrected in both the PDF and HTML versions of the Article.The original version of this Article also had errors in one figure of the Supplementary Information. In Supplementary Fig. 6, the “ε1”,“ε2” axis of panel b, c were mis-aligned. In the same figure, the “Frequency” axis corresponding to the “Imfεbulkg” axis of panel e was mis-aligned. In …