Electronic Nematicity in the Pnictide Superconductors

The iron pnictides are a recently-discovered class of high-temperature superconductors. The phase diagrams of these materials have a lot in common with other unconventional superconductors such as the cuprates. In particular, a superconducting dome is observed for the pnictides as a function of chemical doping, and magnetic order is seen in the underdoped side of the phase diagram. The electronic structure in the magnetic phase is nematic, ie, it breaks the translational symmetry of the underlying lattice. I will describe scanning tunneling microscopy and spectroscopy measurements on the NaFeAs pnictide system, where we can directly observe the electronic nematicity. I will address the relationship between the nematic electronic structure and superconductivity in the pnictides, and also comment on the phenomenology of the pnictides in comparison to the cuprates.