Electron Transportation And Magnetism Property Of "10-3-8" And "1111" Type Iron-Based Superconductors Under High Pressures

As a macroscopic quantum phenomenon,superconductivity has been an important branch and research hotspot of condensed matter physics since it was discovered.At present,superconducting materials are widely used in electric power,military,medical,transportation and other fields.People have been committed to finding superconducting materials with higher transition temperature.The discovery of iron-based superconducting materials is a significant progress in the field of superconductivity.It is the second kind of high-temperature superconductor discovered after copper-based superconductor,which has rich physical properties and great potential application value.However,the mechanism of high temperature superconductivity is still not completely clear,which is a hot and difficult research topic in the field of superconducting materials.In addition,it is of great significance to increase the superconducting transition temperature and explore the superconducting mechanism of iron-based superconductors.Pressure is a kind of"pure"means,which can change the physical properties of materials without introducing impurities.It is found that physical pressure can improve the superconducting transition temperature of iron-based superconductors and provide a new way to explore the mechanism of superconductivity.This paper mainly introduces the research results of iron based superconductors under high pressure conditions,and studies two kinds of iron based superconductors under high pressure.With diamond anvil cell combined physical property measurement system under high pressure and magnetic measurement system of iron-based superconductor resistance,on the hall coefficient,critical magnetic field and magnetization measurements,observed some interesting physical phenomena,and carries on the analysis and discussion,this research to explore the superconducting mechanism of iron-based superconductor provides experimental support and data accumulation,is of great scientific significance and research value.First,we measured the resistivity of Ca₁₀?Pt₃As₈?(Fe_0.95Pt_0.05)₂As₂)₅ single crystalline iron superconductor with complex structure under different hydrostatic pressure?maximum pressure P=5.24 GPa?with temperature change,and found that the T_c-P phase diagram presented an arch trend within the whole pressure range of 0.77 GPa⁵.24 GPa,which was consistent with the results of some high pressure research on iron superconducting materials.By measuring the high pressure magnetization of the sample,it is found that the superconducting transition temperature T_c,m measured by magnetic method are consistent with the results of electrical measurement.In addition,the measurement of high-pressure Hall coefficient found that the material is mainly electron-type carriers,and with the pressure increases,the Hall coefficient decreases,that is,the carrier concentration increases,and the Fermi surface structure changes,which may affect the superconductivity.It is also believed that the change of the superconducting transition temperature of the iron-based superconductor is directly related to the As-Fe-As bond angle of the iron-arsenide layer and the height of the anion As relative to the Fe layer.Then,we measured the high pressure resistivity,Hall coefficient,magnetoresistance and magnetization of the iron-based superconductor CaFe_0.88Co_0.12AsF of the"1111"system?maximum pressure P=16.80 GPa?.It is found that the superconducting transition temperature of the material decreases monotonically with the increase of pressure,but the Hall coefficient of the material is almost constant,which means that the carrier concentration n and the Fermi surface are not affected by the pressure.According to Landau-Fermi liquid theory?FL theory?,we studied the relationship between sample resistivity and temperature T under different pressures,and found that the quadratic term coefficient A decreased with the increase of pressure,while the residual resistivity was almost unchanged,which indicated that the electronic correlation strength was the reason affecting the change of superconducting transition T_c.