| In recent years,topological insulators have set off a wave of research in the field of condensed matter physics.Topological insulators are a new class of quantum matter states.Due to the spin-orbit coupling effect and the protection of time inversion symmetry,the body states of these substances are in the energy-gap insulating states,while the surface states are in the metal states without energy gaps.The surface state of a topological insulator is determined by the topological properties of the bulk electronic state.And as long as the body state is insulating,its edge state always exists stably and is not easily affected by non-magnetic impurities and defects.In this way,electrons can pass through the channels of the topological insulator in an orderly and unobstructed manner.This kind of low energy dissipation transport property has great scientific research value and potential application value in the fields of basic research,spin electronics and quantum computers.The 4f electron orbital in the Sm atom in this system is very local and appears as local magnetism.The 5d orbital electrons in the conduction band and the 4f electrons in the local Sm ions a re coupled to each other,forming a quasi-bound state,shielding the local magnetism of the 4f electrons,and a Kondo effect occurs.5d orbital electrons and local 4f electrons are hybridized to cause band inversion,resulting in non-mediocre topological insulator.Researchers around the world have carried out a lot of research on SmB6 material,and most of these works focused on bulk SmB6.Thin film material has the advantages of large specific surface area and easy integration in the electronic devices.So it is important to prepare high quality SmB6 thin film.Compared with massive studies on bulk SmB6,the work of film growth and characterization of SmB6 is limited.Considering the importance of SmB6 thin film in practical applications,in this thesis we grow SmB6 thin film using pulsed laser deposition(PLD)technology by optimizing the deposition parameters,and characterize the properties of SmB6 thin film by a variety of characterization methods.Its content is mainly divided into two parts,as shown in the following:(1)Using MgO as the substrate,SmB6 thin film was deposited at different temperatures by PLD.(100)oriented crystalline SmB6 films were obtained successfully.Through different testing and analysis methods,the following properties were studied in details:Structure and morphology:The surface roughness and resistivity of SmB6 film grown at different temperatures decreased first and then increased with the increase of the depositing temperature.When the growth temperature was 700℃,the sample has the best crystalline.Its resistivity was the lowest,and the surface roughness is minimal.Electrical property:We used PPMS to study the transport property of SmB6 thin film at low temperatures.Metal-to-insulator phase transition is observed in the sample prepared at 700℃.The resistivity gradually increases with decreasing temperature and finally reaches saturation because the SmB6 film only has a surface state at very low temperatures.(2)YIG/SmB6 heterojunction was prepared by PLD.XRD,AFM,AGM,TEM,etc.were used to characterize the physical properties of the heterojunction.The spin pumping effect was used to study the spin current generation and transport.We detected a strong ferromagnetic resonance signal of the YIG layer,but did not observe the spin pump voltage signal on the surface of SmB6.Ferromagnetic resonance peak position shifts a little.It may be due to the presence of the YIG/SmB6 interface reaction which has an effect on the magnetic properties of YIG.In order to prevent the YIG and SmB6 interface from reaction,2 nm Au was deposited at the interface.But the spin pumping signal is still not observed,and the reason is still not clear and further investigation is needed. |
