Study Of The Large Magnetoresistance Materials By High Resolution Mobility Spectrum Method

The study of topological quantum materials is one of hotspots in the field of condensed matter physics in recent years due to their unique electronic band structure and anomalous quantum transport properties.Generally,topological quantum materials have multiband effect and large magnetoresistance.In this dissertation,we systematically studied the electronic transport properties of the Weyl semimetal TaAs and TaP,topological material PtBi₂ and Ag₃Sn based on maximum entropy mobility spectrum analytical approach,and obtained the following main results:1.In TaAs,four bands with different mobility were clearly distinguished from the mobility spectrum.At T=1.8 K,we found that two bands e_I?13.42 m²/Vs?and h_I?6.39 m²/Vs?with extremely high mobility mainly contribute to the conductivity,but the two low mobility bands e_II and h_II have minor role on the transport properties.Besides,the mobility of e_I is much larger than that of h_I,but decreases faster than that of h_I with increasing temperature,indicating that the high mobility of e_I band is intimately linked to the weyl fermions,and the origin of large magnetoresistance may be related to weyl fermions in lower temprature.Intriguingly,as magnetic field increases,complicated curvature changes of Hall resistivity were observed at T=80 K,meanwhile,the number of bands which contribute to the conductivity were increased from two to four above 80 K.All these results suggest that the electronic structure may be changed around 80 K.Lastly,the carrier concentrations of the electron and the hole band is comparable,signifying that the origin of large magnetoresistance may be related to the electron-hole compensation effect in higher temperature.2.Mobility spectrum also distinguished four bands with different mobility in TaP.At T=2 K,it is found that two high mobility bands significantly contribute to the conductivity,and two low mobility bands almost have no influence on the conductivity.The electron and hole concentrations are almost the same,which means the large magnetoresistance in TaP is also related to the possibly of electron-hole compensation effect in origin.In contrast to TaAs,the hole band mobility is larger than that of electron band at low temperatures and fields.3.Mobility spectrum shows five bands with different mobility in PtBi₂,consistent with the result of first-principle calculation.One hole band with higher mobility?0.964 m²/Vs?,possibly corresponding to the Dirac cone,contributes 15%to the conductivity.The carrier concentrations of electron and hole bands are unequal,which means the large magnetoresistance in PtBi₂ is not related to the electron-hole compensation.In addition,the mobility of all bands gradually decreases with increasing temperature,but the shape of the mobility spectrum substantially not changes,indicating that the electronic structure is not changed below 20 K.4.The mobility spectrum of Ag₃Sn also shows multiband characteristics at low temperature,including three electron bands and three hole bands.The sign of Hall resistivity is positive,indicating the hole band dominate the transport properties,regardless of the higher mobility of electron band.The carrier concentration of the electron band and the hole band is not alike,which means the large magnetoresistance in Ag₃Sn is not related to the compensation of electron and hole.Further detailed analyses suggest that the origin of the large magnetoresistance may be related to Dirac cone state in Ag₃Sn.