Effect of spin-density wave fluctuations on the specific heat jump in iron pnictides at the superconducting transition

Measurements of the specific heat jump at the onset of superconducting transition in the iron-pnictide compounds revealed strong variation of its magnitude as a function of doping that is peaked near the optimal doping. We show that this behavior is a direct manifestation of the coexistence between spin-density wave and superconducting orders and the peak originates from thermal fluctuations of the spin-density waves near the end point of the coexistence phase - a tetracritical point. Thermal fluctuations result in a power-law dependence of the specific heat jump that is stronger than the contribution of mass renormalization due to quantum fluctuations of spin-density waves in the vicinity of the putative critical point beneath the superconducting dome.