Transport Properties On Topological Semimetals Fe₃Sn₂ And In_xTaS₂

As a new class of topological matters,topological semimetals have become a hot research topic in condensed state physics because of their rich physical properties and potential applications.A series of measurements of angle-resolved photoemission spectroscopy(ARPES)and transport prop-erties have verified the relevant theories and deepened the understanding of topological semimetals.According to the magnetic monopole wrapped in the Fermi surface,topological semimetals can be divided into Dirac semimetals,Weyl semimetals and node-line semimetals and so on.In this thesis,the anomalous Nernst effect of ferromagnetic Dirac semimetal Fe3Sn2 and anisotropic supercon-ductivity of topological node-line semimetal InxTaS2 have been studied by means of thermal and electrical transport measurements.The relation between topological bands near Fermi energy and transport properties is analyzed.The innovative achievements we acquired are as the followings:(1)The thermoelectric transport properties of ferromagnetic Dirac semimetal Fe3Sn2 with Kagome lattice structure have been measured,and a giant anomalous Nernst effect has been ob-served.The anomalous Nernst coefficient |Qs| can reach 13.3 ?VK-1T-1 at 300 K,nearly ten times larger than that of usual ferromagnets.The anomalous transverse Peltier conductivity ?yxA shows a linear temperature dependence,which is consistent with Berry-curvature contributions.Fe3Sn2 has an abnormally large ?yxA/?yxA ratio.Considering the Fermi level close to the Dirac cone,the increased ?yxA and ?yxA/?yxA ratio indicate that the massive Dirac dispersion and Berry curvature should play an important role in the giant anomalous Nernst effect.(2)The topological node-line semimetal superconductor InxTaS2 with noncentrosymmetric structure has been successfully synthesized by vapor transport method.A2×2 commensurate charge density wave(CCDW)is observed at low temperature in InxTaS2,identified by transport properties and scanning tunneling microscope measurements.What is more important is that the anisotropic superconductivity emerges below Tc=0.69 K and the anisotropy ratio is significantly enhanced compared to 2H-TaS2.By analyzing the effective mass of InxTaS2 in different directions,we suppose that the enhanced anisotropy could result from the decreased effective mass in the ab plane due to the linear band crossings near the Fermi surface.