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Ryotaro Arita Searching for novel unconventional superconductors with high Tc has been one of the most fascinating challenges in condensed matter physics. One promising approach is, to look for analogs for high Tc cuprates or iron pnictides. Especially, for the former, since its seminal discovery, there have been a variety of proposals. In this talk, I will start with a discussion on the material dependence of Tc in cuprates [1]. In order to explore why the single-layered cuprates, La2£x(Sr/Ba)xCuO4 (Tc~40K) and HgBa2CuO4 (Tc~90K), have such a significant difference in Tc, we recently studied a two-orbital model that incorporates the dz2 orbital on top of the dx2£y2 orbital[1]. It is found that the dz2 orbital contribution to the Fermi surface, which is stronger in the La system, works against d-wave superconductivity. This result suggests that, in order to realize single-orbital analogs of cuprates, it is crucial to minimize the hybridization with other orbitals. From this point of view, by means of LDA+DMFT, I will discuss how we can make d1, d7, and J=1/2 analogs of cuprates in Sr2VO4, Ba2VO4[2], (Nd/Eu)2-xSrxNiO4[3], and Sr2IrO4, Ba2IrO4[4] for which superconductivity has yet to be observed. [1] H. Sakakibara et al., Phys. Rev. Lett. 105 057003 (2010) [2] R. Arita et al., Phys. Rev. B 75, 174521 (2007) [3] M. Uchida, et al., Phys. Rev. Lett. 106 027001 (2011) [4] R. Arita et al., in prep. |