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	空間反転対称性のない系             The study of noncentrosymmetric superconductors is an interesting subject. Noncentrosymmetric superconductors have been extensively investigated since the discovery of superconductivity in CePt3Si. Materials without spatial inversion symmetry has a unique property that the degeneracy of bands with spin up and spin down is lifted in the presence of spin-orbit coupling. In this case, spin singlet and spin triplet Cooper pairs can coexist to form a mixed pairing state. Examples of noncentrosymemtric superconductors are 　　 CePt3Si 　(Tc = 0.75K) 　 　LaPt3Si 　　UIr 　　(under pressure) 　　CeRhSi3 　　Li2Pd3B 　　Li2Pt3B 　　CeIrSi3 　　LaNiC2 　(Tc = 2.7K) The existence of line nodes in the gap function is suggested for CePt3Si, Li2Pd3B and Li2Pt3B. We are interested in LaNiC2 which exhibits relatively high temperature superconductivity with Tc = 2.7K among these compounds.　 The isostructural compound YNiC2 also shows superconductivity when Th is substituted for Y. The maximum of Tc is Tc &sim 8.3K in Y0.5Th0.5NiC2 [2]. We have carried out the first principles calculation for LaNiC2 [3]. Recently, the time reversal symmetry (TRS) breaking has been observed through zero-field muon spin resonance [4]. This is very interesting since the TRS breaking strongly suggests unconventional superconductivity. References [1] W. H. Lee et al.: Solid State Commun. 101 (1997) 323. [2] K. J. Syu et al.: Solid State Commun. 141 (2007) 519. [3] I. Hase and T. Yanagisawa: J. Phys. Soc. Jpn. 78 (2009) 084724. 　"Electronic Structure of RNiC2 (R = La, Y, and Th)" [4] A. D. Hiller et al.: Phys. Rev. Lett. 102 (2009) 117007. [5] J. Quintanilla et al.: Phys. Rev. B82 (2010) 174511.

	Condensed Matter Physics: Electronics Research Institute