Jump in specific heat at the superconducting transition temperature in Ba(Fe1−xCox)2As2 and Ba(Fe1−xNix)2As2 single crystals

Abstract

We present detailed heat capacity measurements for $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Co}}_x\right)}_2{\text{As}}_2$ and $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Ni}}_x\right)}_2{\text{As}}_2$ single crystals in the vicinity of the superconducting transitions. The specific-heat jump at the superconducting transition temperature $\left(T_c\right)$, $\Delta C_p/T_c$, changes by a factor of $\sim 10$ across these series. The $\Delta C_p/T_c$ vs $T_c$ data of this work [together with the literature data for $\text{Ba}{\left({\text{Fe}}_{0.939}{\text{Co}}_{0.061}\right)}_2{\text{As}}_2$, $\left({\text{Ba}}_{0.55}{\text{K}}_{0.45}\right){\text{Fe}}_2{\text{As}}_2$, and $\left({\text{Ba}}_{0.6}{\text{K}}_{0.4}\right){\text{Fe}}_2{\text{As}}_2$] scale well to a single log-log plot over two orders of magnitude in $\Delta C_p/T_c$ and over about an order of magnitude in $T_c$, giving $\Delta C_p/T_c\propto T_c^2$.