Low Temperature Transport Study On Transition Metal Sulfides

Topological matter has been one of the hottest topic of current research of condensed matter physics,in this thesis,I mainly studied the quantum oscillation of the topological semimetal: N bIr T e₄ and the superconductivity of two2 D superconductors: M oT e₂ and N bSe₂.As a candidate material of the type II W eyl semimetal,the unusual properties of N bIr T e₄ may have potential application in the future quantum devices;As the few nature 2D superconductors,M oT e₂ and N bSe₂ provide a good platform to study the fundamental questions of superconductor in 2D limit,in addition,monolayer M oT e₂ has been predicted to be the 2D topological insulator and topological superconductor,so our work may help to understand the topological physics in these materials.In Chapter 1,we introduce the background knowledge of W eyl semimetal and 2D superconductor,including some unusual properties of W eyl semimetals,such as chiral anomaly and Nonlocal transport and the quantum metal state,Ising Pairing superconductivity in 2D superconductor.In Chapter 2,we describe how to synthesize single-crystal N bIr T e₄ and atomic thin film of M oT e₂ and N bSe₂ with CV D,we also describe the microfabrication process and the device measurement equipments including P P M S,3He cryostat and dilution refrigerator.In Chapter 3,we describe the low temperature transport properties of N bIr T e₄,the Hall resistivity shows multiple carriers dependence and changes from electron to hole as temperature increases,the longitudinal resistivity increases in the magnetic field up to 38 T without saturation,the Shubnikov-de Haas effect reveals a strongly anisotropic fermi surface of N bIr T e₄.In Chapter 4,we describe the superconductivity of two 2D superconductors:M oT e₂ and N bSe₂,we find enhanced superconductivity in M oT e₂ thin film compared to the bulk M oT e₂,further study reveals that with Se doping can also enhance the superconductivity of M oT e₂;As for the N bSe₂,we find the superconductivity transition can exist in 2D limit in the as-grown samples which is consistent with the Berezinskii-Kosterlitz-Thouless?BKT?theory.In Chapter 5,we summarize the works of this thesis.