Study On First Principle And Electrical Transport Of Topological Materials NbGeSb And KHgSb

With the rapid development of the information age,exploring electronic materials with low energy consumption,high density,and high transmission has become the core issue of electronic information devices.The fusion of material science and condensed matter physics provides a new way in the process of searching for new materials.In recent years,the fusion of condensed matter physics and the concept of "topology" has led people to realize that the topology in the eleltronic structure of materials may enable the preparation of electronic devices with excellent physical properties.In the process of searching for new topological quantum materials,people have successfully discovered various novel physical properties such as giant magnetoresistance phenomenon,metal-insulator phase transition,etc through theoretical calculations and experimental verifications,however,the applications of novel physical properties are still far from satisfying people's needs.Therefore,it is particularly important to explore the physical properties of new topological quantum materials.In this papre,first of all,the first-principles calculation is used to study the energy band electronic structure of the new topological semimetal NbGeSb.By studying of the state density,energy band structure,fermi surface and surface states of the bulk states,the NbGeSb energy band structure is found balanced topological properties,besides,energy band reversal occurs during the process of energy band crossing,and shows a large and unusual asymmetry in the range of hybridization gap.Compared with ZrSiS,it has a more abundant and compl ex energy band structure.And the band structure further shows that NbGeSb has good metal lic behavior,at the same time,the three-dimensional properties of the fermi surface indicates transport properties of NbGeSb crystal have good three-dimensional characteristics,and the surface electronic structure characteristics of completely different properties are also found in the surface states of different termination surfaces which indicates novel physical characteristics.Based on the first-principles calculation of the topological semimetal NbGeSb,the electrical transport properties of the NbGeSb single crystal were carried out.With the help of spherical aberration corrected transmission electron microscopy and scanning electron microscopy,the crystal quality and crystal structure of single crystal growth were clarified,and comprehensive physical properties were tested by PPMS whicih provides low temperature and magnetic field.Using the four-wire method,results show that NbGeSb has obvious metallic behavior and low resistivity,besides,obvious unsaturation and anisotropy have been found in magnetoresistance.The phenomenon of negative magnetoresistance due to chiral anomalies was observed under the low magnetic field and low temperature.The phenomenon of negative magnetoresistance is most obvious when the direction of the electric field coincides with the magnetic field.At the same time,The symmetry has been uniformly verified in the study of anisotropic angular magnetoresistance.The first-principles calculations studied the energy band electronic structure of the new topological insulator KHgSb in two dimensions.The energy band structure indicates that it is a zero-gap semiconductor in single layer of KHgSb.When considering spin orbit coupling,an energy gap will be opened at the fermi level,and it is found that the metal insulator phase transition occurs during the thickness of the KHgSb from one layer to six layers.The surface electron morphology of the "hourglass fermions" was observed in the(010)crystal plane in the surface state.When a single layer of KHgSb is injected with different amounts of electrons,the fermi level can be adjusted in energy band structure so that the electrical properties can be changed.In this paper,the electronic structure and transport properties of the new topological semimetal NbGeSb and topological insulator KHgSb were studied,we observed the negative magnetoresistance phenomenon caused by the chiral anomaly at low temperature of NbGeSb and predicted that different termination surfaces correspond to completely different surfaces states,besides,the physical phenomena such as phase transitions of metal insulators in different thicknesses of KHgSb,electric field control of single-layer energy band structure are predicted,which enriches the research on the magneticresistance and surface state of topological semimetals,and complements the study of KHgSb thin layer energy band structure,and provides theoretical thinking for the direction of the next experiment.