The Minimum Model for the Iron-Based Superconductors

A single band t-U-J1-J2 model is proposed as the minimum model to describe the superconductivity of the newly discovered iron-based superconductors R(O1-xFx)FeAs and RO1-xFeAs (R = La, Ce, Sm, Pr, Nd, Gd). With the mean-field approach, it is found that the pairing occurs in the d-wave channel. In the likely parameter region of the real materials, by lowering temperature, the system enters firstly the dxy superconducting phase with D4h-symmetry and then enters the time-reversal-symmetry-broken dxy + idx2-y2 superconducting phase with C4h-symmetry. (condensed matter: electronic structure, electrical, magnetic, and optical properties)