Spin-triplet superconductivity. New quantum condensed state in ruthenate

Spin-singlet electron pairs (Cooper pairs), the total spin S=0, causes ordinary superconductivity, for example, the high-temperature superconductivity of copper oxide. However, spin-triplet atomic Cooper pairs, S=1, causes superfluidity of liquid helium. Is there the spin-triplet state in superconductivity? Lately, it was found that the superconductivity of Sr2RuO4 was caused by the spin-triplet state. Sr2RuO4 is the same lamellar crystal structure as the high-temperature superconductivity copper oxide. Copper oxide shows anomalous electron state, but the normal conductive state of liquid helium is described quantitatively as quasi-two-dimensional Fermi liquid The electron orbital of ruthenate is degenerated. So that, copper oxide shows spin-singlet superconductivity of ant-parallel spin pairs depend on dominant anti-ferromagnetism interaction between electrons. On the other hand, ruthenate produce spin-triplet superconductivity of parallel pairs depends on spin fluctuation in the large scale of wavelength. Sr2RuO4 is able to grow so pure crystal that we expect to research the spin-triplet superconductivity so deeply as to the spin-triplet superfluidity of herium3. In this paper, the recent results of Sr2RuO4 are explained on the spin-triplet superconductivity state, the strongly correlated electron system, the superconductivity symmetry, characteristic superconductivity phenomena of spin-triplet degenerate state and mechanism of superconductivity. (S.Y.)