Anomalous Transport Properties Of Weyl Semimetals Ln(Ln=L,Ce,Pr)AlGe Systems

Topological semimetals have been believed to be the unique quantummaterial system because of the characteristics of linear energy band crossing near Fermi level.According to the degeneracy of energy band overlap,topological semimetal s can be divided into topological Dirac semimetals,topological Weyl semimetals and topological Nodal-Line semimetals.Weyl points with topological stability and definite chirality characteristics can be effectively controlled by magnetic field,pressure,and doping,et.al.As a result,they always exhibit strange quantum phenomena and anomalous physical properties.In particular,recently Ln Al Ge/Si(Ln=La,Pr,Ce)Weyl semi-metallic compounds with different rare earth elements,show rich magnetic properties such as non-magnetic,ferromagnetic or antiferromagnetic ordering depencency on Ln.Moreover,the electronic structure of Weyl nodes and the type of Weyl fermions in the system strongly depend on the rare earth element s Ln(Ln=La,Ce,Pr),showing novel physical phenomena.In this dissertation,we grew the high quality Ln Al Ge(Ln=La,Pr,Ce)single crystal using self-flux methods,and reported the abnormal physical properties of the system by measuring the magnetoresistance effect and abnormal Hall effect.The main results obtained are as follows:(1)Large La/CeAlGe single crystals were grown by self-flux method.Crystalstructure and chemical composition of single crystals were confirmed by X-ray diffraction and energy dispersive X-ray spectroscopy,respectively.c With the increase of magnetic field,the magnetization in ab-plane exhibits typical ferromagnetism,and a-axis is easily magnetized axis.Magnetorasistiance(MR)also shows strong anisotropy.At low temperature,it in ab plane shows uniaxial MR with the increase of magnetic field,while it in the c direction shows negative MR.Hall effect at low temperatures shows that Ce Al Ge exhibits a small anomalous Hall effect in the ab-plane,and the maximum anomalous Hall coefficient is 0.068cm~3/C.In the c direction the only normal Hall effect is observed.(2)Large PrAlGe single crystals were also grown.The magneto-resistance and susceptibility measurements of Pr Al Ge indicate that the system shows strong anisotropy behaviors.c-axis is easily magnetized and samples undergoes a ferromagnetic transition below 16K,while it in the ab plane exhibits an antiferromagnetic behavior.Pr Al Ge exhibits obvious anomalous Hall effect in the c direction,and we obtained the normal and anomalous Hall coefficients by fitting those data.Further research indicates that the intrinsic Hall effect may be caused by nontrivial berry curvature.