Imaging the New Iron-Arsenic High-Tc Superconductors

Twenty-two years after the original discovery of high-Tc superconductivity in the cuprates, superconductivity was discovered at high temperatures in a new, second family of materials: the iron arsenides. We summarize the excitement in this rapidly evolving new field of physics, and we present the first scanning tunneling spectroscopic imaging study of a single crystal iron-arsenide superconductor, at magnetic fields up to 9 T. We find an inhomogeneous superconducting gap, which is indicative of strong correlation. We further observe a static disordered vortex lattice at 9 T, and demonstrate that vortices are pinned in the bulk of this material. Finally, we observe dilute strong scatterers whose spectroscopic signatures may prove useful in determining the pairing symmetry in these materials. Reconciling our investigations of the iron-arsenides with similar studies in the cuprates may constrain and guide theories of high-Tc superconductivity.