Elastic Anomalies Associated with superconducting phase transitions in Iron-based Superconductor Ba(Fe1−xCox)2As2

We have measured the temperature dependence of elastic constants of iron pnictide superconductors Ba(Fe1−xCox)2As2 with optimal doped x = 0.060 and over-doped 0.116, with different superconducting phase transition temperatures Tsc. We have observed remarkable anomalies at Tsc. The coupling between the superconducting order parameter and elastic strain was discussed based on the elastic anomaly at Tsc. The elastic constant (C11+C12+2C66)/2 shows a large anomaly at Tsc, which clearly indicates a large Grüneisen parameter of this system. The amount of Grüneisen parameter is 62 comparable to that of the strongly correlated electron system.