Spintronic THz Wave Emitter: an approach from Topological Weyl Semimetal Heusler alloys

为了实现研究目标，我研究了Weyl Heusler合金Co2MnGa的太赫兹辐射。我已经获得了具有不同化学有序的Co2MnGa的THz发射的系统数据。以往的研究认为，在单层铁磁体(而不是Weyl半金属)中，由于反常霍尔效应(AHE)，铁磁层内部的激光激发电子由于来自衬底或盖层的后向散射而产生回流电流，并发出太赫兹波。这种背向散射过程强烈地依赖于薄膜的厚度、粗糙度等结构性质。因此，我还重点研究了Co2MnGa薄膜的THz发射的厚度依赖关系，以深入了解后向散射通过AHE诱导THz发射的机制。对于生长在MgO衬底上的Co2MnGa薄膜，我发现了强烈的特征，即THz发射的起源是由Co2MnGa中的Weyl性质增强的AHE。此外，我还研究了Co2MnGa的THz发射与组份的关系，以阐明Wyle点相对于费米能级的位置如何影响THz发射。在几次会议上讨论了这些结果，并提交了这份文件。

To achieve the research objectives, I investigated the THz emission from Weyl Heusler alloys Co2MnGa. I have obtained systematic data for the THz emission in Co2MnGa with different chemical ordering. According to the past research it was believed that in a single layer ferromagnet (not Weyl semimetals) the laser-excited electrons inside the ferromagnetic layer generates a back-flow current due to back scattering from substrate or capping layer which emits a THz wave due to anomalous Hall effect (AHE). Such back-scattering process strongly depends on the structural properties like thickness, roughness, and etc. Thus, I also focused on thickness dependence of the THz emission from Co2MnGa films to gain insight into the mechanism of the back scattering-induced THz emission via AHE. For thin regime of Co2MnGa films grown on MgO substrates and capped by the MgO layers, I found the strong signature that the origin of the THz emission was AHE which was enhanced by Weyl nature in Co2MnGa. In addition, I have investigated the composition dependence of the THz emission of Co2MnGa to clarify how the Wyle point location with respect to the Fermi level influences the THz emission. Those results were discussed in several conference meetings and the paper was submitted.