Calorimetric Evidence Of Multiband Superconductivity In Ba(Fe0.925co0.075)(2)As-2 Single Crystals

We report on the determination of the electronic heat capacity of a slightly overdoped (x=0.075) Ba(Fe1-xCox)(2)As-2 single crystal with a T-c of 21.4 K. Our analysis of the temperature dependence of the superconducting-state specific heat provides strong evidence for a two-band s-wave order parameter with gap amplitudes 2 Delta(1)(0)/k(B)T(c)=1.9 and 2 Delta(2)(0)/k(B)T(c)=4.4.