Conductance asymmetry in point-contacts on epitaxial thin films of Ba(Fe0.92Co0.08)2As2

One of the most common observations in point-contact spectra on the recently discovered ferropnictide superconductors is a large conductance asymmetry with respect to voltage across the point-contact. In this paper, we show that the antisymmetric part of the point-contact spectrum between a silver tip and an epitaxial thin film of Ba(Fe0.92Co0.08)(2)As-2 shows certain unique features that have an interesting evolution with increasing temperature up to a temperature far above the critical temperature T-c. We associate this observation with the existence of a gap above T-c that might originate from strong fluctuations of the phase of the superconducting order parameter. (C) 2010 American Institute of Physics. [doi:10.1063/1.3460274]