Research On The Electronic Transport Properties Of Quasi-two-dimensional Quantum Materials SrIn₂P₂ And ?-PdBi₂

Topological materials are quantum materials with nontrivial topological band structure.And the topological materials host topologically protected surface state where the electrons have their spin locked to lattice vector highly.Due to the special surface state and band structure of topological materials,a great deal of intriguing physical phenomena are observed,such as high carrier mobility,high anisotropy abnormal negative magnetoresistance caused by chiral abnormal,quantum oscillation effect,and quantum anomalous hall effect,etc.The unique physical properties of topological materials make it possible to fabricate electronic devices with low power consumption and high transmission which can be widely employed in the fields of spintronics,optoelectronics and magnetoelectricity.With the continuous studies,researchers have predicted more unique topological categories and topological materials.Topological insulators,topological semimetals and topological superconductors have attracted much attention and recently become the focus in condensed matter physics and materials science.The paper exhibits the electronic transport properties of two quasi-two-dimensional quantum materials Sr In₂P₂ and?-Pd Bi₂.The main research contents and experimental results are as follows:1.The weak localization effect of quasi-two-dimensional topological insulator candidate Sr In₂P₂single crystalThe theory predicts that the quasi-two-dimensional Zintl phase compound Srin₂P₂ may be a potential topological insulator under lattice stress.We prepare the high-quality Sr In₂P₂ single crystal and measure the electrical transport properties of Sr In₂P₂ single crystal without lattice stress at low temperature and high magnetic field.The resistance of Sr In₂P₂ single crystals at zero magnetic field decreases with temperature decreasing and has a minimum value around Tc?136 K.Below Tc the resistance upturns rapidly,behaving a similar metal-semiconductor transition.Besides,we measure the longitudinal resistance of Sr In₂P₂ crystal under Tc and find the obvious negative magnetoresistance(MR)effect.Further analysis suggests that the negative magnetoresistance is originated from three-dimensional weak localization effect.By three-dimensional weak localization model to fit the magnetoresistance curves at different temperatures,we get the inelastic scattering lifetime dependence on temperature and conclude that the dominant dephasing mechanism is electron-phonon interaction.The Hall resistance at different temperatures further suggests that the weak localization is affected by carrier transportation process.2.The size effect of quasi-two-dimensional topological superconductor candidate?-Pd Bi₂The quasi-two-dimensional?-Pd Bi₂ single crystal is a potential topological superconductor with superconductor transition temperature Tc=5.3 K.We prepare?-Pd Bi₂nanosheets of different thicknesses by nanofabrication technologies and study the influence of size effect on electrical transport properties.As the thickness of?-Pd Bi₂ nanosheets decreases from 85 nm to 50 nm,the superconducting transition is suppressed.When the thickness of?-Pd Bi₂ nanosheets is reduced to 45 nm,the superconducting transition eventually disappears and the resistance at low temperature rises slowly,behaving similar metal-semiconductor transition As the thickness is 30/36 nm,the resistance upturns suddenly around 7 K and hardly changes below 7 K,showing a high resistance state,which is inhibited by the external magnetic field.Besides,the?-Pd Bi₂ nanosheets below 45 nm shows obvious negative magnetoresistance effect and the Hall resistance of?-Pd Bi₂ indicates that the electrons dominate the transport in?-Pd Bi₂nanosheets.The behavior similar to superconductor-insulator transition in?-Pd Bi₂ can originate from the destroyed long-range phase coherence suppressing the superconductivity with the thickness decreasing.With further reducing the thickness,the electron localization is enhanced,which makes the resistance increase.