Superconductivity And Topological Properties Of Ternary Metal Compounds

The research of high temperature superconducting materials has always been the focus of condensed matter physics.Scientists have been exploring high-temperature superconducting materials,hoping to realize more applications of superconducting materials in practical production.But up to now,it has been found that the critical transition temperature of most superconductors is too low,while the pressure required by some predicted high-temperature hydrides superconductors to reach the critical transition temperature is too high,which greatly limits the application of superconductors.On the other hand,since the discovery of topological insulators,finding new topological states has become the core of condensed matter physics.With the emergence of Dirac semi-metal and Weyl semi-metal,the research interest in topological phenomena has shifted to various topological metals or semi-metals.Recently,a great deal of work has been devoted to the study of superconductivity and topological physics of ternary metal compounds.Hydrogen-dominated metal alloys may be potential high-temperature superconducting materials under high pressure,because of the light weight of hydrogen and high Debye temperature.Ternary metal hydrides are a convenient and valuable system for studying metallization and superconductivity of metal hydrides,because they can be synthesized under lower requirements and recovered under environmental pressure.At present,the hot research field of applied physics and materials science is how to make hydrogen-rich materials play their metallic and super-conductivity,thus forming metallization of hydrogen materials and forming high-temperature superconducting structures.The recently discovered sulfur trihydride(H₃S),which can realize superconductivity at ultra-high temperature,has set a new record in this field.it can realize superconductivity transition temperature up to 203K.this discovery is a major research breakthrough in the transition of superconductor structure to superconductivity at room temperature,which has aroused extensive attention and research on this superconductor at home and abroad,and promoted the use and research of superconductivity at high pressure.Recently,the conductive behavior and structural phase transition of hydrogen-rich metal hydride Li₅Mo H₁₁ have been discovered The Li₅Mo H₁₁ changes from insulator to weak metal at about 100GPa.Superconductivity was observed at 100 GPa,which changed from insulator to weak metal at this pressure and kept at 210 GPa,and the maximum initial transition temperature was 6.5 K at 160GPa.In our research,however,the maximum superconducting transition temperature of stable(Eu₂H₆Ru)₄ compounds at 160GPa is about 25.8 K.(Eu₂H₆Ru)₄ is already a metal under normal pressure,so it does not need to change from insulator to metal,but directly changes from metal to superconducting phase.moreover,in their research,the T_c value is not very large at 160GPa,so the(Eu₂H₆Ru)₄ we studied under this pressure can have higher superconducting transition temperature.Recently,a new topological fermion,namely cubic dispersed Dirac semimetal(CDSM),has been proposed theoretically.Due to the strict limitation of crystal symmetry,the substance of this CDSM is extremely rare,only the quasi-one-dimensional molybdenum chalcogenide A₂Mo₆X₆(A=Na,K,Rb,In,TL;X=S,Se,Te);It is the main candidate to realize these cubic Dirac fermion;When the interacting electrons are confined to a reduced dimension in space,they show a more singular electronic ground state,which makes them a fascinating research topic in theory and experiment.Quasi-one-dimensional systems provide an excellent place to explore the low-dimensional electron correlation,because they show a variety of physical phenomena,including non-Fermi liquid behavior,superconductivity,charge density wave distortion and so on.We mainly choose Tl₂Mo₆Se₆ as the research object,which is also superconducting under environmental pressure.In this paper,the pressure evolution of Tl₂Mo₆Se₆ band structure up to 150 GPa is studied by first-principles calculation,with special attention to its topological properties.We found that there may be topological phase transition in P6₃/m structure below 50 GPa.When it exceeds 50 GPa,structural phase transition will occur,thus entering topological trivial phase.The corresponding relation of body boundary is also studied,which clearly reveals the dramatic change of surface state under pressure.The calculated phonon spectrum reveals the possible Peierls distortion in this system.The prediction of this work will open the way for further study of new physical properties related to this series of quasi-one-dimensional topological compounds.Our results establish Tl₂Mo₆Se₆ as an ideal place to further explore various topological phenomena related to different types of topological fermions,and may be helpful to design these nontrivial carriers in future applications.