Theoretical Study on Superconductor - Magnet Multilayers

对非常规超导体和巡游铁/反铁磁体组成的多层膜的电子性质进行了理论研究。我们处理一个紧束缚模型在一个正方形晶格上的吸引（排斥）最近的邻居网站（现场）之间的相互作用来描述超导性（磁性）。在平均场近似下，我们导出了描述超导序参量和磁化强度空间变化的Bogoliubov de Gennes（BdG）方程。这些BdG方程数值求解完全自洽的方式。我们发现：（1）在超导体与（反）铁磁体的界面附近，由于I邻近效应，出现了SCOP与磁化共存的表面态。(2)在界面附近，诱导出与体相不同对称性的SCOP。特别是，即使SCOP在体相中具有自旋单重态对称性，也会出现自旋三重态SCOP。我们还考察了杂质的影响，因为杂质总是存在于真实的体系中，所以为了将理论结果与实验结果进行比较，有必要考察杂质对超导态的影响。(3)结果表明，在杂质周围诱导出了与体相不同对称性的SCOP。此外，自发自旋电流可以出现在具有自旋轨道相互作用的磁性杂质附近。

Theoretical study has been carried out on the electronic properties of multilayers composed of unconventional superconductors and itinerant ferro/antiferromagnets. We treat a tight binding model on a square lattice with attractive (repulsive) interactions between nearest-neighbor sites (on-site) to describe the superconductivity (magnetism). Then we derive the Bogoliubov de Gennes (BdG) equations which describe the spatial variations of superconducting order parameters (SCOP) and magnetization using mean-field approximation. These BdG equations are solved numerically in a fully self-consistent way. We found the following :(1) Near the interface between the superconductor and the (anti)ferromagnet, surface state where SCOP and magnetization coexist appears due to the I proximity effect.(2) Near the interface the SCOP's with different symmetries from that of the bulk are induced. In particular, even if the SCOP has a spin-singlet symmetry in the bulk, spin-triplet SCOP can occur.We have also examined the effect of impurities, since they always exist in real systems, and so it is necessary to examine the effect on the superconducting state in order to compare the theoretical results with experiments.(3) It turns out the SCOP s with different symmetries from that of the bulk is induces around the impurity. Also spontaneous spin currents can appear near a magnetic impurity with spin-orbit interactions.