The Magneto-transport Property Study Of Several Single Crystalline Materials

Magneto-transport property is one of the most important physical properties of materials.Giant magnetoresistance(GMR)was found in magnetic multilayer materials in 1988 and has been widely used in magnetic storage devices.With the further research on topological quantum materials(including topological insulator,Dirac/Weyl semimetal,Dirac nodal-line semimetals,etc.),the extremely large magnetoresistance effect of these materials has aroused great interest.Elucidating the physical origin of extremely large magnetoresistance in topological quantum materials not only riches the research of condensed matte physics,but also guides on how to exploring the materials with extremely large magnetoresistance effect in the viewpoint of applications.In this thesis,magneto-transport phenomena and corresponding physical pictures are predicted through single-and two-carrier model,under different approximations.Combing single-and two-carrier model and electronic band structures predicted by the first-principles calculation,the magneto-transport data Cu2T1Te2/Se2,ZrSiS,HfTes and MoTe2 single crystals are rationalized.A unified explanation on magneto-transport properties of diverse crystals is given.The conclusions are summarized as follows:1)Cu2T1Se2 is a single hole-carrier metal.The conduction band and valence band is partially overlapped in Cu2T1Te2 and electron doping by Cu2+ ions makes Cu2T1Te2 an electron-hole coexisting semimetal at the low temperature.2)The large magnetoresistance effect in ZrSiS is due to the nearly compensated electron and hole carriers,as well as high carrier mobility,the open orbital in the Fermi surface results in the anisotropic and extremely large magnetoresistance.3)HfTe5 is a kind of narrow band-gap semiconductor.The change of electron/hole carrier concentration leads to a resistance peak on the temperature-dependent resistance curves.We can modify the carrier properties through controlling the Te defect concentration.Resultantly,the temperature of maximum resistance can be adjusted within the 50-90 K.In addition,the magnetoresistance effect can reach as large as 30000%by means of co-existence of electron and hole.4)The results of the carrier model in the MoTe2 system are consistent to those extracted from quantum oscillation analysis.It turns out that electrons and holes coexist in this material.Due to its low mobility of about 103 cm2/(V·s),the magnetoresistance is only 1000%,indicating that high mobility(>105 cm2/(V·s))is crucially important to the extremely large magnetoresistance effect.These conclusions on magneto-transport properties of single crystalline materials,reached by combining single-/two-carrier transport model and electronic band structure calculated by the first-principles calculation,are crucial to understand the physical properties of topological quantum materials.These works also have some hints on how to improve the transport properties of materials in the viewpoint of applications.