ANOMALOUS ELASTIC BEHAVIOR AND ITS CORRELATION WITH SUPERCONDUCTIVITY IN IRON-BASED SUPERCONDUCTOR <font>Ba</font>(<font>Fe</font>_1-x<font>Co</font>_x)₂<font>As</font>₂

Abstract

Elastic properties of iron-based superconductor Ba ( Fe 1-x Co x ) 2 As 2 with various Co concentrations x were reviewed. Among all elastic constants, C 66 shows remarkable softening associated with the structural transition from tetragonal to orthorhombic. The amount of anomaly in C 66 is 90% for the underdoped samples of x &lt; 0.07 For the overdoped samples, the anomalies in C 66 gradually disappear with the increasing of Co concentration. The elastic compliance S 66 (= 1/C 66 ) shows a quantum critical behavior, which behaves just like the magnetic susceptibility of unconventional superconductors. There exists a clear correlation between the superconducting transition temperature and the amount of anomaly in S 66 . It was suggested that the structural fluctuation, which is measured by S 66 , plays an important role in the emergence of superconductivity. The elastic anomaly of Ba ( Fe 1-x Co x ) 2 As 2 is characterized by a strong electron–lattice coupling, which would be originated from the 3d orbitals of iron. This might be a universal phenomenon not only in iron-based superconductors but also d-electron based superconductors. The results on Ba ( Fe 1-x Co x ) 2 As 2 would reveal relevant roles of the structural fluctuations due to the orbitals, which should be taken into account for the understanding of a whole picture of the superconductivity in iron-based superconductors and related materials.