Karl Franzens University Graz
Graz University of Technology
|
|
| |
Karl Franzens University Graz | Graz University of Technology | |
Electronic structure of new superconductors The discoveries that cuprates can be made to superconduct below transition temperatures reaching up to 150 K have been followed by discoveries of other classes of high-temperature superconductors, most notably the "graphites" MgB2 and CaC6, and the recent discovery of iron pnictides and chalcogenides. Whereas the mechanism behind the superconductivity in the cuprates remains not understood, the one in the graphites was soon unveiled as the classical electron-phonon interaction. Largely due to density-functional electronic-structure calculations, this could be cleared up within months. Such calculations have so-far contributed little to theories of cuprate superconductivity, but they did predict many results of angle-resolved photoemission experiments, and they have revealedmaterials trends. The iron pnictides and chalcogenides resemble the cuprates in many respects. They are pd-electron systems with the d-electrons residing on a 2D square lattice, and they are antiferromagnets, which upon doping become superconductors. However, whereas the undoped cuprates are single-band Mott insulators, the undoped iron compounds are metals which seem to be well described by itinerant multi-band theory. I shall describe the basics of this, but leave the solution many puzzles, including the origin of the superconductivity to future research. |