ELECTRONIC STATES OF (GaP)m(AlP)n SHORT PERIOD SUPERLATTICES AND MULTI-QUANTUM WELL STRUCTURES AND THE MECHANISM OF PHOTOLUMINESCENCE

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This three-year research project started on April of 1996 and has been conducted successfully. The aim of this project was twofold : One was to elucidate the origin of the unusual behavior of photoluminescence (PL) observed in (GaP)n(AJIP)n short period superlattices, in which the PL intensity decreases with increasing a magnetic field in the strong field regime in the Faraday configuration. In the present research we have clarified that a bound exciton trapped at a pseudo-dot type defect at the interface is responsible for the above unusual behavior. The present result was appreciated in the field of semiconductors and we have given a talk in international conferences. Another aim was to clarify a many-body electronic structures of underdoped cuprates. By using the multi-configuration self-consistent field variational method for a single CuO_5 pyramid embedded in YBCO7 with Tc=90K and then by introducing the transfer interactions between CuO_5 pyramids, unusual electronic states were clarified. That is, the dopant holes move coherently by taking the Zhang-Rice spin singlet and Hund's coupling triplet alternately in the apin correlated region of anti-ferromagnetic ordering due to Cu localized spins, without destroying the anti-ferromagnetic order.