Large Anisotropic Uniaxial Pressure Dependencies of Tc in Single Crystalline Ba(Fe0.92Co0.08)2As2

Using high-resolution dilatometry, we study the thermodynamic response of the lattice parameters to superconducting order in a self-flux grown Ba(Fe0.92Co0.08)(2)As-2 single crystal. The uniaxial-pressure dependencies of the critical temperature T-c calculated using our thermal-expansion and specific-heat data via the Ehrenfest relation, are found to be quite large and very anisotropic (dT(c)/dp(a)=3.1(1) K/GPa and dT(c)/dp(c)=-7.0(2) K/GPa). Our results show that there is a strong coupling of the c/a ratio to superconducting order, which demonstrates that T-c is far from the optimal value.