Symmetry measurements of the order parameter of BaFe$_{2}$As$_{2}$ superconductors

Since the discovery of the Fe-pnictide superconductors, extensive efforts have been directed toward understanding the symmetry and mechanism of the superconducting pairing. Extended s-wave models, predominantly the s$\pm$ model, are predicted by many theories, but a definitive experimental verification has been elusive. In this case, the phase-sensitive Josephson interferometry measurements that have been effective in determining the symmetry of many superconductors do not give a definitive signature. As an alternative approach, we are searching for proximity-induced structure in the density-of-states of an s-wave superconductor proximity-coupled to Co-doped BaFe$_2$As$_2$ superconductive crystals. Unique features are predicted to arise for s$\pm$ pairing that allow this symmetry to be distinguished from other order parameter forms such as s++ or d-wave. Observation of this structure would provide both magnitude and phase information about the multigap structure of the BaFe$_2$As$_2$ crystal.