Quasiparticle Interference of C2-Symmetric Surface States in a LaOFeAs Parent Compound

We present scanning tunneling microscopy studies of the LaOFeAs parent compound of iron pnictide superconductors. 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 wave vectors exhibits pronounced twofold (C-2) symmetry, strongly reminiscent of the nematic electronic state found in CaFe1.94Co0.06As2. The implications of these results to the electronic structure of the pnictide parent states will be discussed.