Elastic properties of iron-based superconductor SrFe 2 (As 1−x P x ) 2

Abstract We have measured the transverse elastic constants C 44 and C 66 of iron-based superconductor SrFe 2 (As 1− x P x ) 2 (Sr122) single crystals as a function of temperature. Under-doped samples show elastic anomalies towards the structural/magnetic transition temperature. Optimal sample shows an upturn at the superconducting transition temperature in both C 44 and C 66 . These behavior is similar to Ba122, while only C 66 shows anomaly for Ba122. The elastic anomalies were analyzed by Jahn-Teller formula, and it was found that the Jahn-Teller energy of C 44 is much larger than that of C 66 . This indicates that monoclinic structural fluctuations exist inherently in Sr122 in addition to the known tetragonal fluctuations. Co-existence of these diverse fluctuations and their cooperation are a key to investigate the mechanism and properties of superconductivity in iron based superconductors.