The Effect Of Mn Incorporation In Transition Metal Sulfides Mn_xTaS₂

Recent years,the exploration of novel topological states has injected new vitality into the forefront research of condensed matter physics.In order to induce topological phase transitions,experimental techniques such as doping,intercalation,pressure application and electromagnetic modulation are commonly used to control the physical state of materials.Some special spiral magnetic phases,such as chiral magnetic solitons and magnetic Skyrmions,can lead to non-trivial Berry curvature in the system,which in turn gives rise to special electronic structures and anomalous transport properties in materials.It has been found that intercalation effect in transition metal sulfides has a significant impact on the structure and physical properties of the system.Based on two-dimensional layered transition metal sulfides,this dissertation mainly focuses on the study of Mn intercalation effects in TaS₂ system.We grew a series of single crystals with different Mn contents,and performed detailed electrical and magnetic transport measurements.In the experiment,we first discovered the anomalous Topological Hall Effect（THE）in the system,which strongly depends on the variation of Mn content,and the experimental results are agree well with theoretical models.The separated chapter content of this dissertation is listed as follows:Chapter 1 describes the Lagrangian equation of phase space and the Boltzmann transport equation to derive the relationship between electrical conductivity and Berry curvature,analyzing the influence of Berry curvature on thermal and electrical transport properties and providing theoretical explanations for anomalous transport phenomena.In addition,the research background,related transport properties,and unresolved issues of the two-dimensional transition metal sulfide（TaS₂）system are emphasized,and the motivation of this dissertation is elaborated.Chapter 2 introduces the experimental methods and instruments,including solid-phase reaction and gas-phase transport for preparing single crystals,X-ray diffraction for characterizing lattice structure,scanning electron microscopy for observing morphology,and X-ray energy-dispersive spectroscopy for analyzing elemental ratios.The measurement methods for thermal and electrical transport are also introduced in detail.Chapter 3 mainly studies the transport properties of Mn_xTaS₂ samples with different Mn doping contents,through a series of experiments methods.（1）A series of high-quality Mn_xTaS₂（0.1≤x≤0.3）single crystal samples with different Mn doping contents were successfully grown,and it was found that the low-temperature magnetic ground state of the system is affected by the Mn content.（2）The anomalous THE in this system was first observed at low temperatures,which strongly depends on the Mn contents.because the reason is that the Mn moments form a spiral magnetic ground state,producing a non-zero Berry curvature in real space,thereby causing an anomalous THE.This study provides new ideas for the development of topological magneto-electronics and the preparation of two-dimensional devices.Chapter 4 is the summary and the proposition of my project,including the preparation process of Mn_xTaS₂ single crystal samples,their structure parameters and characterizations,as well as magnetic and electrical transport properties of those samples.