Evidence of Landau Level broadening due to strain fluctuations in single-layer graphene

Abstract

The Landau Level (LL) broadening mechanisms in graphene were investigated through a quantitative analysis of magneto-micro-Raman experiments in two different samples, namely a natural single layer graphene (SLG) flake deposited over a Si/SiO2 substrate and a multilayer epitaxial graphene (MEG) sample. Interband LL transition widths were extracted from the dampening of the magnetophonon resonances associated with optically active LL transitions crossing the energy of the E2g Raman-active phonon. Our results on the MEG samples are similar to previous reports and consistent with LL energy widths proportional to B^{1/2}. On the other hand, SLG shows a much stronger dampening of the low-field resonances that is consistent with an additional broadening mechanism with LL energy widths proportional to B^{-1/2}. This contribution is argued to be a signature of random strain-induced pseudomagnetic fields that take place in SLG samples and are absent in self-protected MEG