Refined infrared magnetotransmission experiments have been performed in magnetic fields B up to 35 T on a series of multilayer epitaxial graphene samples. Following the main optical transition involving the n=0 Landau level (LL), we observe a new absorption transition increasing in intensity with magnetic fields B≥26 T. Our analysis shows that this is a signature of the breaking of the SU(4) symmetry of the n=0 LL. Using a quantitative model, we show that the only symmetry-breaking scheme consistent with our experiments is a charge density wave (CDW).
Fig 1 : CR energies, resulting from the deconvolution of the experimental transmission traces, as a function of B for two samples. The full lines are a linear fit of the data for the low energy transition at low and high field.
More details in L.Z. Tan et al., Phys. Rev. B 91, 235122, (2015)