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 ${\mathrm{CaFe}}_{1.94}{\mathrm{Co}}_{0.06}{\mathrm{As}}_2$. The implications of these results to the electronic structure of the pnictide parent states will be discussed.

• Received 1 September 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.087001