Key elements of Iron pnictide superconductors

David Singh gave a nice talk today about the iron pnictide superconductors. Here are just a few of the points that he emphasized.

This is a big family of materials - high Tc is a very robust phenonema. Common features

• Fe atoms are in a square lattice
• near divalent Fe
• tetrahedral coordination (2 Fe per unit cell)

The connection of the pnictides to the cuprates is weak, contrary to what some people asserted in the early days [because of the proximity of superconductivity and antiferromagnetism]
-doping not essential to superconductivity
-Mott physics is not relevant (no Mott insulating state)
-magnetic order & superconductivity do co-exist?
-multiple orbitals are present [they may be important for avoiding Mott insulator]
-many materials are electronically "three-dimensional" rather than two-dimensional

[ARPES and dHvA see significant corrugation of the Fermi surface].

Proximity of superconductivity to a magnetically ordered phase should not be viewed as necessarily implying a magnetic mechanism for Cooper pairing. He gave a summary [in the form of a phase diagram] of the 1966 paper by Berk and Schrieffer who argued that Pd was actually not superconducting due to proximity to a ferromagnetic state.

An important case is fullerene superconductors. They are due to electron-phonon pairing, but can be close to an antiferromagnetic Mott insulating phase.