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

Ferromagnetic Semiconductor(FS) with magnetic and semiconducting properties united in one material shows some unique characteristics in physics, crystallography, op-tics, and so on, then owns a broad prospect of application. D-wave superconductor(SC) is one representative kind of unconventional superconductors. After a simple conversion and development, generally, theoretical results for the d-wave superconductor can be directly applied to other unconventional SCs. Recently, so-called superconducting spintronics, has being gradually proved to be one of the most attractive subjects of spintronics. By measuring some basic parameters of the d-wave SC junctions, one can get the information of pairing mechanisms and energy gap. Therefore, the study of the d-wave SC junctions is important meaningful.In this article, we extend the BTK theory to study an FS/d-wave SC/FS junction and obtain the variation of the relevant probabilities, conductances, and tunnelling mag-netoresistance (TMR) with energy, in the meantime, compare the results with those for corresponding s-wave SC junctions.The FS/d-wave SC/FS junction are studied from three aspects in the article. Firstly, we study the effects of interband coupling on the relevant reflection and transmission probabilities, differential conductances, and TMR with energy for β the angle between the crystal a axis and the interface normal0and π/4. It is found that due to the interband coupling, for an incident heavy hole from the left FS, there are not only the inherent Andreev and normal reflections but also novel Andreev and normal reflections. With the change of the interband coupling, the features of the behaviors for the reflection and transmission probabilities with energy are basically not changed, however, the amplitudes are different. We also find that the differential conductances decrease with increasing α and decrease more and more quickly. When Z is larger, the TMR basically keeps unchanged.Secondly, we study the effects of barrier strength on relevant probabilities, differential conductances, and TMR. It is shown that with the enhancement of barrier strength, some probabilities increase while others are suppressed. Also the conductance and TMR are found to decrease with Z increased.Finally, we compare the results of the conductance for the d-wave model with those for s-wave one. It is found that for the d-wave, due to the anisotropic of energy gap, the first peak value is bigger than those of others no matter what the value of Z is, while for the s-wave, the first peak value is smaller than those of others regardless of value of Z. Particularly, at bigger Z, there is a split of the peak at the gap energy, whereas the situation for the s-wave is just contrary. All these characteristics in the junctions can be used to probe the pairing symmetry of d-wave SC.