The question of interaction between two different orders is always an
intriguing one – will they coexist or will they fight for the phase space; how
will each of them be modified by this interplay? In this talk I will present a
weak-coupling approach to describe the interaction between two electronic
orders: superconductivity (SC) and spin-density wave (SDW).
These two orders are the primary players in the iron-based superconductors
discovered in the early 2008. Specifics of the electronic structure of these
materials and its variations between different families create a wide range of
possibilities for competition or attraction between SC and SDW states.
I will describe how this interplay depends on parameters, such as doping and
symmetry of the SC state. I will also touch on thermodynamic properties of the co-existence state, and on its behavior in magnetic field.