Study On The Superconductivity Of FeSe_1-xTe_x And ZrNCl With Alkali Metal Intercalated

Iron-based superconducting system is one of the most promising high-temperature superconducting systems after the cuprates superconductors.The iron-based superconductor and the copper oxide superconductor have a similar layered structure,which is formed by alternately arranging the conductive layer and the carrier library layer along the c axis.The FeSe superconductor of the"11"system is the simplest structure in the iron-based superconducting system;its layers are joined by van der Waals forces.The"11"system can be converted into other systems such as"111"?"122"and"1111"by various means such as intercalation or doping,and obtain many complex and interesting quantum physical properties.In addition,the solid ion conductor field-effect transistor(SIC-FET)is the latest carrier regulation method.It takes into account the advantages of all-solid-state device preparation of traditional field-effect transistors(FETs)and the powerful carrier regulation capability of electric double-layer field-effect transistors(EDL-FETs).Using SIC-FET to adjust the carrier concentration of the band insulator material ZrNCl and observing its superconductivity is helpful to understand the superconducting mechanism.1.The?-phase FeSe superconducting material was obtained by high-temperature solid-phase synthesis,and then synthesized K0.3(NH3)y Fe2Se2 and K0.6(NH3)y Fe2Se2intercalation compounds at room temperature by liquid ammonia method.Both of these superconductors have a layered structure similar to the precursor tetragonal FeSe,but the distance between layers has increased significantly.More importantly,the interlayer spacing is not positively correlated with the amount of potassium ion insertion.K0.3(NH3)y Fe2Se2 with less potassium ion insertion has a larger interlayer spacing.The two intercalated compounds have pure Tc?43K and Tc?30K superconducting phases,which are significantly higher than the superconducting transition temperature of the precursor?-FeSe of about 8.5K,and have a larger Fe-Se interlayer distance K0.3(NH3)y Fe2Se2 appears as a high Tc phase.External pressure can inhibit the two superconducting phases Tc?43K and Tc?30K,but the pressure suppression effect of Tc?43K phase is larger than that of Tc?30K phase.The inhibitory effect of the applied pressure indicates that in the high Tc phase,the interlayer coupling effect of FeSe is weaker.2.The FeSe_1-xTe_x superconducting material was synthesized by partially replacing Se with Te,and then synthesized K0.3(NH3)y(FeSe_1-xTe_x)2 and K0.6(NH3)y(FeSe_1-xTe_x)2 series of materials,where x=0-0.6.Depending on the amount of K inserted,these materials have a superconducting phase of Tc?40K or Tc?30K,respectively.We also found that there are two phase separations of Te-poor and Te-rich in the FeSe_1-xTe_x,when 0.1<x<0.5,and both the Te-poor phase and the Te-rich phase can be co-intercalated by K with ammonia,but only the K-ammonia co-intercalated Te-poor phase is the main cause of superconductivity.The negative chemical pressure of Te replacing Se causes negligible changes in Tc in the K0.3(NH3)y(FeSe_1-xTe_x)2 series,but leads to obvious suppression in Tc in K0.6(NH3)y(FeSe_1-xTe_x)2series.In both systems,the superconductivity disappeared when the Te content x?0.4.3.The ?-ZrNCl single crystal samples was synthesized by a two-step gas phase transport method,and ssuccessfully modulated electrical properties of ZrNCl thin flakes used a newly developed SIC-FET device,which usede the solid lithium ion conductive glass ceramics as the gate dielectric and substrate.Drived Li⁺in the solid lithium ion conductor substrate into the?-ZrNCl thin flakes,we have induced the optimal superconductivity with a midpoint critical temperature T_c^mid=15.1 K.In addition,we also found that ZrNCl is a low carrier concentration of the superconductor,in its superconductor-insulator transition edge has abnormal behavior peculiar,its T_c increases with decreasing carrier concentration,which provides an attractive new platform for studying the BCS-BEC transition.