铁基超导体Fe1+yTe1-xSex中磁性的中子散射研究

本文对本研究组主要的研究领域——利用中子散射研究铁基超导体系Fe_1+yTe_1-xSe_x中磁性与超导的相互作用进行简要综述. Fe_1+yTe_1-xSe_x具有和其他铁基、铜基超导体相似的相图——母相Fe_1+yTe是反铁磁体, 随着Se掺杂的增加, 母相的反铁磁序受到抑制, 随后在x～30%处体超导出现, 在x～50%处达到最佳掺杂, 此时超导转变温度T_c～ 15 K, 达到整个体系在常压下的T_c最大值. 它们的相图又存在着差别: 在相图末端, 即当Se掺杂达100%时, Fe_1+ySe 仍然超导, T_c～8 K. 该体系母相磁有序的面内波矢大致为(0.5,0) (采用每个原胞含2个铁原子的四方结构), 随着Se含量的增加, 在超导逐渐发展的同时, 磁激发谱的谱重被逐渐转移到波矢为(0.5,0.5) 处. (0.5,0.5) 处在温度低于T_c 时出现中子-自旋共振峰. 施加外磁场后, 超导受到抑制, 该共振峰也被压制. 从这些实验结果我们得到以下的结论: 在这个体系中磁性和超导紧密耦合在一起——(0.5,0) 处的静态磁有序与超导互相竞争, (0.5,0.5) 附近的自旋激发则可能对超导电性的形成具有重要的促进作用. 本文还将简要讨论磁性的来源和3d 过渡金属的替代效应.     

Multi-carrier transport in ZrTe_5 film

Single-layered zirconium pentatelluride(ZrTe_5)has been predicted to be a large-gap two-dimensional(2D)topological insulator,which has attracted particular attention in topological phase transitions and potential device applications.Herein,we investigated the transport properties in Zras a function of thickness,ranging from a few nm to several hundred nm.We determined that the temperature of the resistivity anomaly peaktends to increase as the thickness decreases.Moreover,at a critical thickness of～40 nm,the dominating carriers in the films change from n-type to p-type.A comprehensive investigation of Shubnikov–de Hass(SdH)oscillations and Hall resistance at variable temperatures revealed a multi-carrier transport tendency in the thin films.We determined the carrier densities and mobilities of two majority carriers using the simplified two-carrier model.The electron carriers can be attributed to the Dirac band with a non-trivial Berry phaseπ,while the hole carriers may originate from surface chemical reaction or unintentional doping during the microfabrication process.It is necessary to encapsulate the Zrin an inert or vacuum environment to potentially achieve a substantial improvement in device quality.