Interplay Between Magnetism And Superconductivity In Iron-based Superconductors And Annealing Effects In BiS₂Based Superconductors

This essay gives an explicit introduction to the development of study on iron-based superconductors since2008. We put our emphasis on the interplay between magnetism and superconductivity. We also provide useful discussions on specific cases of vortex dynamics.In Chapter1, after offering brief introduction to the categorization and prac-tical applications of superconductors, we comprehensively review the magnetism in the iron-based superconductors. We perform induction from the aspects of phase diagram, magnetic ordering and spin dynamics.In Chapter2, a work by myself is introduced concerning the122-structure compound AxFe2-ySe2. Based on that, we come to discuss the basic property of the AxFe2-ySe2series. As the doping by different elements on Fe site leads to totally contrasting effects on superconductivity, we curiously look for the reason by performing different measurements and finally found it via micro-scale magnetism study. We offered useful discussions for the interaction between magnetism and superconductivity in AxFe2-y/Se2.In Chapter3and4, we turn our focus to the vortex dynamics. We use high quality AxFe2-ySe2single crystal as our research object, and discuss the motion of the vortex and the applicability of vortex-glass model for layered compounds. Finally we verify the correctness of our theoretical analysis via fittings for the data.In Chapter5, we testify the superconductivity reported in the new type su-perconductors:the BiS2-based superconductors and annealed the originally insu-lating parent compound Bi6O8S5, and successfully induced its superconductivity. We gave discussions to the effects of the annealing concerning micro-structure adjustments and element redistribution.