Quasiparticle interference of C$_{2}$-symmetric surface states in LaOFeAs parent compound

We present scanning tunneling microscopy studies on the LaOFeAs parent compound of iron pnictide superconductors [1]. High resolution spectroscopic imaging reveals strong standing wave patterns induced by quasiparticle interference of two-dimensional surface states. Fourier analysis shows that the distribution of scattering wavevectors exhibits pronounced two-fold (C$_{2})$ symmetry, strongly reminiscent of the nematic electronic state found in CaFe$_{1.94}$Co$_{0.06}$As$_{2}$ [2]. The implications of these results to the electronic structure of the pnictide parent states will be discussed. \\[4pt] [1] X.Zhou \textit{et al.} arXiv:1008.2642 \\[0pt] [2] T.M.Chuang \textit{et al.} Science \textbf{327}, 181 (2010)