Study Of Transition Metal Bismuth/Tellurium Compounds Under High-Pressure

Experimental condensed matter physics mainly studies the interaction between(quasi)particles,structure,energy band,physical/chemical/mechanical properties in condensed matter.Many novel ordered states and quantum phenomena appear in condensed matter due to the many-body interactions.Discovering and understanding these novel ordered states and quantum phenomena is the basis for understanding quantum mechanical effects in macroscopic materials,and the quantum materials bearing these properties provide the basis for further applications.Therefore,it is very important to understand the properties of these ordered states and the interactions between them.The focus of this paper is to use physical pressure as a tuning parameter to manipulate and study various phase transitions and their related ordered states,including superconductivity,magnetic order,charge density waves,structural phase transitions,etc.In this paper,the structure and electrical properties evolution of topological semimetal y-PtBi2,ferrimagnetic nodal-line semiconductor Mn3Si2Te6 and two-dimensional charge density wave material LaTe3 are studied under high pressure by using X-ray diffraction,Raman scattering and electrical transport measurements combined with density functional theory.The findings include the following:1)Pressure-induced superconductivity in γ-PtBi2.The pressure-induced superconductivity in y-PtBi2 with non-trivial triple degenerate fermions exhibiting unsaturated XMR effect has been investigated by XRD and electrical transport experiments.The critical pressure is 5-6 GPa and the beginning temperature of the superconducting transition is～2 K,showing a very weak pressure dependence over a wide pressure range of～5-48 GPa.The lattice structure of γ-PtBi2 remains stable at 12.9 GPa.Near the critical pressure where SC appears,Hall coefficient changes dramatically,and the change of sign from positive(hole dominated)at low pressure to negative(electron dominated)at high pressure may indicate a close relationship between them.2)Pressure engineering of colossal magnetoresistance in the ferrimagnetic nodalline semiconductor Mn3Si2Te6.Ferrimagnetic nodal-line semiconductor Mn3Si2Te6 exhibits exotic magnetotransport behavior,termed colossal angular magnetoresistance.By studying the effects of pressure on the electrical and magnetic properties of single crystal Mn3Si2Te6,we found a pressure-induced semiconductor-to-metal transition between 1.5 and 2.5 GPa,and a possible structural transition/amortization at 12 GPa.Both DC magnetization and density-functional theory calculations show that the ferrimagnetism gradually stabilizes as the pressure rises rising to at least 10 GPa,which is also reflected by a monotony increase in the Curie temperature TC.However,the CMR effect only appears in the semiconductor state and is significantly suppressed,and finally disappears in the metal state.These findings provide important insight into the microscopic interplay between non-trivial band topology and intrinsic magnetic order.3)Pressure-induced superconductivity in quasi-two-dimensional charge density wave material LaTe3.The RTe3 system(R:rare-earth elements except Eu/Yb/Lu)shows a complex phase diagram under pressure due to the interaction of charge density waves,antiferromagnetism,and superconductivity.However,the relationship of interactions between these ordered states remain unclear.The interaction of quasi-particles,the evolution of structures and transport properties in LaTe3 under high pressure have been systematically studied using high-pressure methods including Raman,electrical transport and synchrotron radiation XRD experiments.The results show that the Raman amplitude mode and a phonon mode have anti-cross behavior when the pressure is changed,which is similar to the situation with temperature.Combined with the results of electrical transport and the evolution of structure,it is found that with the increase of pressure,the pressure first suppresses the charge density wave and induces the superconductivity.With the further increase of pressure,the isostructural phase transition occurs near 28.8 GPa,and the superconducting transition temperature reaches the highest point.At 47.0 GPa,a further structural phase transition occurs and causes Hall coefficients to change sign.These findings provide new insights for further understanding of the relationship between various ordered states in the phase diagram of typical charge density wave materials RTe3.