TOPICS Developments of Magnetic Measuring System i-Helium3 Measurements under Extreme Conditions Crystal Growth under Ultra Low Oxygen Partial Pressure Novel Transition Metal Oxides New Ferromagnetic Transition High-Conductive Oxide Researches on Novel Superconductivity Spin-Triplet Superconductivity Mechanism of High-Tc Superconductivity MgB2 Superconductivity Novel Quantum Simulation Techniques New Quamtum Monte Carlo Simulation Dynamical Cluster Method
	The high-Tc cuprates have the typical perovskite structure with the 2D Cu-O planes. The mechanism of high-Tc SC is not still resolved although many theories have been proposed.             The origin of superconductivity certainly lies in the two-dimensional plane consisting of oxygen and copper atoms since the high-Tc oxides are quasi two-dimensional materials with large anisotropy. The superconducting gap has d-wave symmetry, and thus a superconductivity originated from the on-site Coulomb repulsion is a candidate for high-Tc superconductivity. We investigate the three-band model with copper and oxygen orbitals or the sinplified single-band Hubbard model.       As in the BCS scenario, two electron with opposite spins near the Fermi surface form the pairing state.
	The size dependence of the SC condensation energy for the Hubbard model. The upper two lines are for the single-band Hubbard model, and the lower two lines are for the three-band Hubbard (d-p model). The diamond indicates the value for optimally doped YBCO. The blue solid line shows the results for the coexistent state of vertical stripes and SC. In this state the charge density has an oscillating component accompanying the spatial oscillation of the SC gap. In the underdoped region the SC competes and collaborates with antiferromagnetism at the same time. Because of the collaboration with AF, the SC can exists even in the low-doping region.
	The figure indicates the LTT crystal structure at low temperatures. In this phase the vertical striped-state with inhomogeneous spin and charge distributions is stabilized and coexists with SC.

	Condensed Matter Physics Group: Nanoelectronics Research Institute