Rafael M. Fernandes
The recent discovery of iron-based compounds displaying superconductivity at nearly 60K opened a new direction in the research of high-temperature superconductors. Much of the interest lies in understanding not only their superconducting pairing mechanism, but also their normal state properties. In this talk, I will show that emergent Ising-nematic degrees of freedom are present in these systems over wide temperature and doping ranges, fundamentally affecting their macroscopic properties and explaining several behaviors observed experimentally. Starting from a microscopic electronic model, I will demonstrate that the nematic state has magnetic origin, and is associated with a spontaneous tetragonal symmetry-breaking. I will discuss the phase diagrams resulting from this model, and how the elastic properties are affected by nematic fluctuations. I will also show that the scattering of electrons by impurities and by spin fluctuations in the nematic phase leads to an anisotropy in the resistivity, whose sign changes from electron-doped to hole-doped compounds.