Study of exotic superconductivity in the iron-family-based intermetallic compounds

本项目研究了几种铁族化合物的奇异超导性和几何挫折效应。特别是在研究硅化铁Lu_2Fe_3Si_5的奇异超导性和尖晶石钴酸盐GeCo_2O_4的几何挫折效应方面取得了显著的研究成果。硅化铁超导体Lu_2Fe_3Si_5具有与砷化铁超导体不同的三维多带结构。本课题研究了非磁性杂质对Lu_2Fe_3Si_5超导性的影响，并进行了磁热输运实验。得到的研究结果有力地证明了逆符号多隙超导性。尖晶石钴酸盐GeCo_2O_4是一种具有轨道自由度的几何挫折磁体，尽管铁磁交换相互作用占主导地位，但仍会发生反铁磁跃迁。GeCo_2O_4的非弹性中子散射实验观察到分子自旋激发的典型受挫效应。此外，在GeCo_2O_4的超声速度测量中，发现了分子自旋激发下的弹性异常，这种弹性异常强烈地表明存在磁场诱导的轨道序序跃迁。

This project performed studies of exotic superconductivity and geometrical frustration effects in several iron-family-based compounds. And remarkable research results were obtained especially in the study of exotic superconductivity in the iron silicide Lu_2Fe_3Si_5, and the study of geometrical frustration effects in The spinel cobaltite GeCo_2O_4.The iron silicide superconductor Lu_2Fe_3Si_5 has three-dimensional multiband structure which is demarcated from the multiband structure in the iron arsenide superconductors. This project performed study of non-magnetic impurity effects on the superconductivity, and magneto-thermal transport experiments in Lu_2Fe_3Si_5. And we obtained research results which strongly suggest the sign-reversed multigap superconductivity.The spinel cobaltite GeCo_2O_4 is a geometrically-frustrated magnet with orbital degrees of freedom, where an antiferromagnetic transition occurs despite the dominance of ferromagnetic exchange interactions. Inelastic neutron scattering experimets in GeCo_2O_4 observed a typical frustration effect of molecular spin excitations. Furthermore, ultrasound velocity measuremets in GeCo_2O_4 observed elastic anomalies driven by the molecular spin excitations, and elastic anomalies which strongly suggest the occurrence of magnetic-field induced orbital order-order transitions.