Theory of coherent charge transport in junctions involving unconventional superconducting materials

Abstract

Recent theoretical studies of coherent charge transport in junctions involving unconventional superconducting materials such as high-temperature superconducting iron-based pnictides (FeBS) and in structures with induced superconductivity which are formed of a thin metal layer with spin–orbit coupling in contact with an s-wave superconductor (S_SO) are reported. The theoretical analysis is performed with our unified approach based on the tight-binding method and boundary conditions obtained for it. This approach makes it possible to take into account a complex nonparabolic and anisotropic spectrum of normal excitations in unconventional superconducting materials and their multiband character, as well as unusual types of symmetries of the superconducting order parameter in them. The possibility of a semiclassical description in the case of intraorbital superconducting pairing is demonstrated. The method of calculations and their results are presented for the conductivities of junctions between a normal metal and unconventional superconducting materials, as well as for the Josephson current. Comparison with the experiment for the junction with FeBS is performed and indicates the presence of the unusual s_± symmetry of the order parameter. An experiment is proposed to test our theoretical results for S_SO.