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

Abstract

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 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.