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The discovery of superconductivity in LaFeAsO1-xFx has stimulated the research activity on new high temperature superconductors [1]. Rare-earth element substitutions for La have boosted Tc up to 55 K [2]. To date, four kinds of iron-containing layered superconductors have been identified [1,3-5]. I will report physical properties of RFeAsO1-xFx (R = La, Sm Nd), Ba(Fe,Co)2As2, and Fe(Se,Te) systems. In RFeAsO1-xFx polycrystals, magneto-optical characterizations of intra- and inter-grain critical current densities (Jc) have revealed large contrast in the two Jc’s [6]. We have succeeded in growing high quality single crystals of the latter two systems. Magneto-optical imagings in optimally doped Ba(Fe,Co)2As2 have clarified rather homogeneous distribution of Jc [7]. In addition to these layered compounds, characteristics of other Fe-containing superconducting compounds R2Fe3Si5 (R = Lu and Sc) will also be reported. Specific heat measurements clearly show the presence of two distinct gaps in these compounds [8], indicating that R2Fe3Si5 are two-gap superconductors like MgB2.


[1] Y. Kamihara, T. Watanabe, M. Hirano, H. Hosono, J. Am. Chem. Soc. 130 (2008) 3296.

[2] Z.-A. Ren, J. Yang, W. Lu, W. Yi, X.-L Shen, G.-C. Che, L.-L. Sun, F. Zhou, Z.-X. Zhao, Europhys. Lett. 82 (2008) 57002.

[3] M. Rotter, M. Tegel, D. Johrendt, Phys. Rev. Lett. 101 (2008) 107006.

[4] X. C. Wang, Q. Q. Liu, Y. X. Lv, W. B. Gao, L. X. Yang, R. C. Yu, F. Y. Li, C. Q. Jin, Solid State Commun. 148 (2008) 538.

[5] F. C. Hsu, J. Y. Luo, K. W. The, T. K. Chen, T. W. Huang, P. M. Wu, Y. C. Lee, Y. L. Huang, Y. Y. Chu, D. C. Yan, M. K. Wu, Proc. Natl. Acad. Sci. 105 (2008) 14262.

[6] T. Tamegai, Y. Nakajima, Y. Tsuchiya, A. Iyo, K. Miyazawa, P. M. Shirage, H. Kito, H. Eisaki, J. Phys. Soc. Jpn. 77 (2008) Suppl. C, 54.

[7] Y. Nakajima, T. Taen, and T. Tamegai, J. Phys Soc. Jpn. 78, 023702 (2009).

[8] Y. Nakajima, T. Nakagawa, T. Tamegai, and H. Harima, Phys. Rev. Lett. 100, 157001 (2008).


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