Recently, superconductivity in the crystal without inversion symmetry has attracted much attention because the Cooper pairing state such as spin-singlet or spin-triplet states may be mixed in these compounds. Both Li2Pd3B and Li2Pt3B which have the same crystal structure without inversion symmetry exhibit the superconductivity below 6.7K and 2.43K,respectively. From the specific heat and the penetration depth measurements, the superconducting state of Li2Pd3B is similar to that of the conventional BCS type with isotropic superconducting gap. On the other hand, in Li2Pt3B those measurements show power law behavior at low temperature, indicating the anisotropic superconducting gap. It suggests the possibility of mixture of spin-singlet and spin-triplet states in Li2Pt3B. In this presentation, I will introduce the physical properties of Li2Pt3B and Li2Pd3B and discuss the difference of superconducting state in these compounds.

　 最近、結晶構造に空間反転対称性の無い超伝導が注目を集めている。このような系においては、spin-singlet状態とspin-triplet状態の２つの超伝導状態が混成する可能性が議論されている。 今回、取り上げたLi2Pd3BとLi2Pt3Bはどちらも結晶構造に反転対称性が無く、それぞれTc=6.7K, Tc=2.43K以下で超伝導性を示す。 比熱や磁場侵入長の測定から、Li2Pd3Bは等方的な超伝導ギャップを持つ典型的なBCS型超伝導体と似た振る舞いを示すことがわかる。一方、Li2Pt3Bは低温で異方的超伝導ギャップに見られる、べき乗の振る舞いを示す。この結果は、spin-singlet状態とspin-triplet状態の混成の可能性を示唆している。 今回、Li2Pt3BとLi2Pd3Bの物性を紹介し、これらの超伝導状態の違いについて議論する。

H. Q. Yuan, et al .Phys. Rev. Lett, 97, 017006 (2006)