| Searching for superconductors with higher Tc has always been a hot topic of condensed matter physics. The iron-based superconductors discovered in the year of 2008 initiated a new round of research upsurge of high temperature superconductivity after the cuprate superconductors. The discovery of iron-based superconducting materials provides us a new point of view to research the high temperature superconducting mechanism and gives us enlightenment to explore the new superconducting materials with higher Tc.In this paper, we carried out experiment research on 1111 phase Iron arsenic superconductors and Iron pnictide superconductors. Main work and results are as follows:(1) 1111 phase SmFeAsO and SmFe1-xCoxAsO(x=0.1, x=0.2) single crystals have been grown successfully by us. A systematic research on their transport properties was carried out, which laid foundation for further studying of angle resolved photoelectron spectroscopy. (2) The effect of non-magnetic Zn impurities on superconductivity of LaFePO0.94F0.06 was studied, and strong magnetic pair-breaking effect caused by Zn was observed. The result suggests a nodal energy gap in this system and a possible scenario of SC paring symmetry.The paper includes four chapters. The first chapter is the introduction, including different structure types of iron-based superconductors and research status of FeP and NiP based superconductors, characteristics of parent compounds and doping effect of Zn impurity in iron-based superconductors. The second chapter introduces preparation of samples and measurement methods of physical properties.In the third chapter, we demonstrate the results of synthesis and transport properties of SmFeAsO and SmFe1-xCoxAsO single crystals. Millimeter-sized single crystals of SmFeAsO and SmFe1-xCoxAsO were grown from NaAs flux by flux growth method for the first time. The method provides a new way for growth of other 1111 phase iron-based superconducting single crystals. Structural analysis shows that samples are of very high purity and have strong c-axis orientation. Meanwhile, Co doping in SmFeAsO leads to the shrink of c-axis. The study of transport properties of parent compound SmFeAsO found that a flat maximum is presented at 140K marking the establishment of SDW-AFM ordering in the Fe-As layers and a sharp peak is observed at low temperature 6K owing to the AFM ordering of the Sm ion sublattice. The SmFe1-xCoxAsO single crystals show a sharp superconducting transition at 14K. Furthermore, measurement of ab-plane resistivity pab and c-axis resistivityρc shows thatρc/ρah～46 for SmFe0.9Co0.1AsO, indicating a large anisotropy and a less dependence on temperature. Overall, the later annealing treatment made the Co content more uniform and sample quality better. In the SmFe1-xCoxAsO system, due to the itinerant nature of Co 3d electrons, the electron-type charge carriers were induced by Co doping, and it was further confirmed by the measurement of Hall coefficient.The fourth chapter reports the effect of non-magnetic Zn impurities on Iron pnictide superconductor LaFePO0.94F0.06.In the LaFePO1-xFx system, we chose the optimal-doped LaFePO0.94F0.06 and made partial substitution of Fe with Zn. We found that lattice parameters a,b,c increases with Zn doping, and that only 1% Zn doping can destroy superconductivity. Node gap superconductors are very sensitive to non-magnetic impurities, so our results are consistent with d-wave or s±-wave SC paring symmetry. |
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