We report specific-heat experiments under the influence of high pressure on a strongly underdoped Co-substituted BaFe2As2 single crystal. This allows us to study the phase diagram of this iron pnictide superconductor with a bulk thermodynamic method
and pressure as a clean control parameter. The data show large specific-heat anomalies at the superconducting transition temperature, which proves the bulk nature of pressure-induced superconductivity. The transitions in the specific heat are sharper than in resistivity, which demonstrates the necessity of employing bulk thermodynamic methods to explore the exact phase diagram of pressure-induced Fe-based superconductors. The Tc at optimal pressure and the superconducting condensation energy are found to be larger than in optimally Co-doped samples at ambient pressure, which we attribute to a weak pair breaking effect of the Co ions.
