Thermal Expansion and Gruneisen Parameters of Ba(Fe1-xCox)2As2: A Thermodynamic Quest for Quantum Criticality

Thermal expansion data are used to study the uniaxial pressure dependence of the electronic-magnetic entropy of Ba(Fe1-xCox)(2)As-2. Uniaxial pressure is found to be proportional to doping and, thus, also an appropriate tuning parameter in this system. Many of the features predicted to occur for a pressure-tuned quantum critical system, in which superconductivity is an emergent phase hiding the critical point, are observed. The electronic-magnetic Gruneisen parameters associated with the spin-density wave and superconducting transitions further demonstrate an intimate connection between both ordering phenomena.