In the limit of perfect nesting, the physics of iron pnictides is governed by the density wave formation at the zone-edge vector $\mathbf{M}$. At high energies, various spin- (SDW), charge-, and orbital/pocket- (PDW) density waves, and their linear combinations, all appear equally likely, unified within the unitary order parameter of $\mathrm{U}(4)\times \mathrm{U}(4)$ symmetry. Nesting imperfections and low-energy interactions reduce this symmetry to that of real materials. Nevertheless, the generic ground state preserves a distinct signature of its highly symmetric origins: A SDW along one axis of the iron lattice is predicted to coexist with a perpendicular PDW, accompanied by weak charge currents. This “hidden” order induces the structural transition in our theory, naturally insures $T_s⩾T_N$, and leads to orbital ferromagnetism and other observable consequences.

• Received 20 November 2010

DOI:https://doi.org/10.1103/PhysRevB.83.020505