Large elastic anomalies and strong electron-lattice coupling in iron-based superconductor Ba(Fe1−xCox)2As2

We investigated the elastic properties of the iron-based superconductor Ba(Fe1−xCox)2As2 with various Co concentrations. The elastic constant shows remarkable anomalies associated with the structural phase transition and the superconducting transition. The elastic constant C66C66 shows a quantum critical behavior, which behaves just like the magnetic susceptibility of unconventional superconductors. It was suggested that the anomalous part in the elastic compliance S66(1/C66)S66(1/C66) is closely related the emergence of superconductivity. Large Grüneisen parameter was found at the superconducting transition in the longitudinal elastic constant. These results show the strong electron–lattice coupling in this system, and support the prevailing scenario on the relevant role of structural fluctuation coupling to orbitals to understand a whole picture of iron-based superconductor.

► Iron-based superconductor shows a remarkable softening in C66C66.
► The anomalous C66C66 shows a quantum critical behavior.
► Elastic properties are characterized by strong electron–lattice coupling.
► The structural fluctuations may play a relevant role for the emergence of superconductivity.