| It is a very important and hot issue to explore new superconducting materials inthe superconducting physics field. Especially, in the research of layered compounds, Ithas been found that many superconducting materials with layered crystal structurealways exhibit exotic physics properties. The typical examples include high-Tccuprates and Fe-based superconductors. The discovery of those superconductors hascaused great research interests in the high Tc superconductors again and again. In2012, superconductivity in the novel superconductor Bi4O4S3with layered crystalstructure has been discovered, followed by LnO1xFxBiS2(Ln=La,Ce,Pr,Nd,)superconductors. These new materials share a common NaCl-type BiS2layer, playingthe crucial role of superconducting layers. Following those results, SrFBiS2compoundwith similar structure was also reported, however, it was a semiconductor and nosuperconductivity is observed down to2K. In this dissertation, we investigated the Ladoping effect in the Sr1-xLaxFBiS2system, and found that superconductivity can beinduced by La-doping in this system. All the polycrystalline samples were synthesizedby the two-step solid state reaction methods, and meanwhile we perform acombination of XRD diffraction, electrical transport, magnetic susceptibility, Hallcoefficient and heat-capacity measurements, confirming that electron-typedsuperconductor in present system. The results show that superconductivity issuccessfully induced by La doping in Sr1-xLaxFBiS2(0.4≤x≤0.7) compounds with amaximal Tc of3.5K at x=0.55; This system shows evident bulk superconductivityand possibly exists multiband effect. Besides, we established the electronic phasediagram of Sr1-xLaxFBiS2(0≤x≤0.7) system. It can be seen that a transition frommetallic to semiconductor-like behavior with doping is observed in the normal state ofthe superconducting samples, and Tc decreases with doping contents. All of theseresults can help us to explore the nature of BiS2superconductor. |
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