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	Multi-Band Superconductivity
	Ru oxide: Sr2RuO4 This oxide has the perovskite crystal sturcture which is the same as that of high- temperaure cuprates. Three d-orbitals play a role in this compound in contrast to cuprates where the dx2-y2 orbital is mainly concerned with superconducivity and magnetism.             The Ru transition metal oxide Sr2RuO4, with the perovskite crystal structure, shows significant spin-triplet superconductivity with Tc = 1.5K. There have been many intensive studies on this material, and the symmetry of Cooper pairs is believed to be p-wave. Strictly speaking, however, the origin of superconductivity is not still clarified. A clear spin-triplet superconductive phase has never been obtained, based on the electronic model for Sr2RuO4. In relation to this material, we have proposed a new multi-band model that exhibits spin-triplet superconductivity. This model has a horizontal line node. In our model the inter-band Coulomb interaction between three orbitals dxy, dyz, dzx play an important role to show a novel superconductivity.       Superconductivity from the Coulomb Scattering Mechanism The superconducting gap has horizontal nodes, as shown in the figure, that originate from the interlayer couplings. Ref. S. Koikegami et al.: Physical Review B67, 134517 (2003).

	Condensed Matter Physics: Electronics Research Institute