Ballistic surface plasmons in high mobility Dirac liquid of graphene

Optical spectroscopies are an invaluable resource for exploring new physic of new quantum materials. Surface plasmon polaritons and other forms of hybrid light-matter polaritons provide new opportunities for advancing this line of inquiry. In particular, polaritonic images obtained with modern nano-infrared tools grant us access into regions of the dispersion relations of various excitations beyond what is attainable with conventional optics. I will discuss this emerging direction of research with two examples from graphene physics: $i)$ ultrafast dynamics of hot photo-excited electrons [2]; and \textit{ii)} ballistic electronic transport at low temperatures [3].$\backslash $pard$\backslash $pard$\backslash $pard[1] D.N. Basov, M.M. Fogler and F. J. Garcia de Abajo ``\textit{Polaritons in van der Waals materials}'', Science 354, 195 (2016).$\backslash $[2] G. X. Ni, L. Wang, M. D. Goldflam, M. Wagner, Z. Fei, A. S. McLeod, M. K. Liu, F.Keilmann, B. \"{O}zyilmaz, A. H. Castro Neto, J. Hone, M. M. Fogler and D. N. Basov \textit{Nature Photonics} \textbf{10}, 244 (2016)$\backslash $[3] G. X. Ni, A. S. McLeod, L. Xiong et al. [in preparation].