Phase-incoherent superconductivity above Tc in Ba(Fe1-xCox)2As2 thin films

Understanding the mechanism of superconductivity in the recently discovered high Tc ferropnictide superconductors is one of the most important problems in contemporary condensed matter physics. It is believed that the normal state properties of these compounds might hold the key to understanding their superconductivity. In this talk, I will discuss our recent point-contact spectroscopy results on high quality epitaxial thin films of             Ba(Fe1-xCox)2As2, a member of the so called 122 family of the ferropnictides. Our results show that Andreev reflection between an epitaxial thin film of Ba(Fe0.92Co0.08)2As2 and a silver tip can be seen in the normal state of the film up to temperature T~1.3Tc, where Tc is the critical temperature of the superconductor. Andreev reflection far above Tc can be understood only when superconducting pairs arising from strong fluctuation of the phase of the complex superconducting order parameter exist in the normal state. Therefore, our results provide spectroscopic evidence of phase-incoherent superconducting pairs in the normal state of the Ba(Fe1-xCox)2As2 thin films.