Synopsis: Back to basics
The condensed matter community’s current excitement over a new class of iron-based superconductors closely resembles the early days in the discovery of high-temperature superconductivity in copper-based (cuprate) oxides. New compounds are being discovered nearly every month, with the highest reported transition temperature approaching 55 K. Similar to the copper-oxide layers in the high- cuprates, the new superconductors consist of conducting iron-arsenide layers that are separated by insulating rare-earth-oxide layers. First-principles calculations have shown that superconductivity is associated with the iron-arsenide layers, but these studies are based on complex models that can only be solved with computational methods and a more intuitive model is required. In a Rapid Communication appearing in the June 11th issue of Physical Review B, Srinivas Raghu and Shou-cheng Zhang of Stanford, Douglas Scalapino of the University of California, Santa Barbara, and collaborators have distilled the current knowledge on this complicated system into a simple model.
They construct an effective Hamiltonian that correctly reproduces the structure of the electronic Fermi surface in the normal state, which is a necessary first step for understanding the superconducting state. They also find magnetic behavior associated with the iron-arsenide layer that is thought to be connected to superconductivity in these materials.
The work may be viewed as the iron-arsenide analog of the classic paper by Zhang and Rice , which introduced an effective Hamiltonian for the cuprates. Such simple models that capture the low-energy physics are indispensable starting points for theorists as they attempt to reproduce the properties of these complex materials. - Alexios Klironomos
 Zhang, F-C. and Rice, T. M. Phys. Rev. B 37, 3759(R) (1988)