High Pressure Effect On Strong Spin-Orbital Coupling Materials

Spin-orbit coupling interaction is a kind of"tiny"splitting of orbital energy level caused by the interaction between the spin of particles and the orbital momentum.Strong spin-orbit coupling interaction can induce many unique quantum phenomenas,such as topological surface states,Rashba effect,p wave superconductors,etc.A series of strong spin-orbit coupling materials,such as binary topological insulators and Rashba compounds,have been studied under pressure,and it has been shown that pressure can effectively induce many new physical properties,such as superconductivity,topological electronic structure phase transition,and so on.These properties have great potentional for application.Therefore,this paper systematically studied the physical properties of several different types of strong spin-orbit coupling materials under high pressure by high pressure experimental technology.The research results are as follows:?1?Investigation on the structure and physical properties of 3D Dirac semimetal Cd₃As₂ single crystal under high pressure.It was found that the resistances of Cd₃As₂exhibited an insulator behavior different from that of metal state at normal pressure and at low pressure.The superconductivity of T_c=2.0 K appeared at 8.5 GPa,and T_c increased to 4.0 K when the pressure further increased to 21.3 GPa.The superconducting transition temperature was found to be abnormally constant before the highest pressure.Synchrotron radiation X-ray diffraction shows that there is a phase transition in the crystal structure around 3.5 GPa.The constant value of T_c and the linear Hc2 dependence of temperature under pressure,as well as the reduction of crystal structure symmetry,indicate that the superconductivity observed in Cd₃As₂ under high pressure may have a topological structure.These results suggest that Cd₃As₂ is a good candidate for topological superconductor.?2?Investigation on the three-dimensional quaternion topological insulator BiSbTeSe₂.Two superconducting phases induced by pressure are found by high pressure electric measurement.The first superconducting phase SC I appeared in 3.2GPa and T_c was about 7 K.With the change of pressure,it showed a basically constant value and presented the anisotropy of superconductivity,which may be related to the topological property.When the pressure continued to increase,the second superconducting phase SC II appeared at 9.6 GPa.The superconducting phase had a significant superconducting transition at 13.3 GPa and T_c was 2.7 K.The highest T_c in SC II phase is about 9.5 K at 22 GPa.Two crystal structures phase transitions were observed at 10.1 GPa and 28.2 GPa by in situ high pressure synchrotron radiation?XRD?,respectively.Hall coefficient measurement showed that the carrier type changed from n-type to p-type at about 3.2 GPa?i.e.,SC I phase?,and turned back to n-type at 9.6 GPa?the first phase change of crystal structure?.Finally,we obtained the pressure-temperature phase diagram of BiSbTeSe₂ under 50.5 GPa,and observed the behavior of topological insulator under pressure more clearly.?3?Investigation on the physical properties of Sb₂S₃ and Bi₂S₃ under high pressure.In Sb₂S₃ single crystal,pressure-induced insulator-metal phase transition and superconducting phase transition were observed at 17 GPa and 35 GPa,respectively.At the same time,it was confirmed that Sb₂S₃ had neither pressure-induced second-order phase transition nor electronic topological phase transition at about 5 GPa.The superconducting transition temperature is proportional to the pressure,and at 98.9 GPa,T_c reaches about 9.7 K.The results of synchrotron radiation X-ray diffraction show that there is a crystal structure transition around 15.1 GPa,which is corresponding to the pressure of the insulator-metal phase transition.A"V"shaped change of resistance around 18.1 GPa may indicate a electron topological transition.Insulator-metal transition and superconducting transition were observed at 18.7 GPa and 49.4 GPa,respectively for Bi₂S₃.The superconducting transition temperature is proportional to the pressure,and reaching 10.9 K at 152 GPa.The results of synchrotron radiation X-ray diffraction show that no crystal structure transition within 55.2 GPa.Through theoretical calculation,it is speculated that the insulator-metal transition may be caused by the slip between layers and S vacancy.