Coherent Quantum Transport In Ferromagnet/S_±-wave Superconductor/Ferromagnet Structures

Iron pnictide superconductors are a new type of materials for superconducting study, and have become.one of the important regions of condensed-matter physics. As faced by all newly discovered superconductors (SCs) with unconventional behavior, one of impor-tant issues for the iron-based SCs is determination of the pair potential symmetry. By measuring essential parameters of the superconductor junction, one can get the informa-tion of the symmetry mechanism and gap energy.In this article, we extend the Blonder-Tinkham-Klapwijk(BTK) approach to study-ing FM/s±-SC/FM junction from two aspects, and obtain the relevant probabilities and conductances. We also compare the results of s±model with those of s++ model.On the one hand, the effects of barrier strength and spin polarization on the relevant reflection and transmission probabilities, and differential conductances are studied. It is found that, for s±model, in different magnetic configurations, transmission probabilities and differential conductances with energy can exhibit different behaviors. Also, we find that, different interband interferences of the two models lead to different effects of barrier strength of interfaces and spin-polarization on the reflection and transmission probabili-ties, and differential conductances with energy. Compared with s++ model, regardless of magnetic configurations, we can obtain the following properties for s±model. Firstly, the AR probability Aσhas two peaks, one is at E/Δ2=1.0, the other is at E/Δ2=0.5, which just indicates two OPs. Secondly, for Z unequal to 0, novel features for Bσat E/Δ2=0.5 with a dip accompanied by a peak and Dσat E/Δ2=1.0 with a dip accompanied by splitting of a peak in both F and AF alignments appear. Thirdly, there is no longer an oscillation peak of tunneling differential conductances at the bigger gap energy and at least one peak is very sharp in both the F and AF alignments.On the other hand, the effects of mixing coefficientα0 and superconducting gap ratioβon the relevant reflection and transmission probabilities, and differential conductances are studied. Asα0=0, the s±-SC reduces to conventional s-wave one, so that the results are the same as those obtained in the corresponding conventional SC tunneling junctions. Withα0≠0, it is found that with the increases of mixing coefficientα0 and superconducting gap ratioβ, the above mentioned three properties have no change. Furthermore, in both models, regardless of the magnetic configurations, the first peak or dip of relevant probabilities and differential conductances is shown to shift to the lower energy whenβis enhanced, these just imply the increase in ratios of OP magnitudes. Therefore, the three properties in the junctions can be used to probe and discern the s±pairing symmetry of iron-based SC in experiments.