Specific-Heat Discontinuity Delta C Vs. T-C In Annealed Ba(Fe1-Xcox)(2)As-2

The low-temperature specific heat of annealed single-crystal samples of Ba(Fe(1-x)Cox)(2)As-2 with compositions spanning the entire superconducting phase diagram was measured. Effort was made to discover the best annealing schedule to maximize T-c and minimize transition width in these samples. Values of Delta C/T-c normalized to 100% superconducting volume fractions varied proportionally to Tc a. Within a rather narrow error bar of +/- 0.15, the exponent a was the same (approximately 2) over a range of compositions (0.055 <= x <= 0.15) around the optimal concentration x = 0.08, where T-c is the maximum in the phase diagram. Thus, whether the superconductivity was coexistent with magnetism (underdoped) or not (overdoped) did not affect the non-BCS variation (alpha nearly 2 instead of approximate to 0.8-0.9 for BCS superconductors) of Delta C/T-c with T-c. The annealed samples in the present work, with increased Delta C/T-c and T-c values compared to previous results for the Ba(Fe1-xCox)(2)As-2 alloy system, suggest that the intrinsic value of the exponent a for the iron superconductors, when the samples are annealed, with fewer defects, may indeed be even further from the BCS value of 0.8-0.9 than previously thought.