Control of Superconducting Properties by Metal Organic Compound/High-T_c Superconductor

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In this research project, new heterostructures comprising of organic compounds such as Cu-phthalocyanine (Cu-Pc), in which carriers can be induced by a visible light irradiation, and high-T_c oxide superconductors such as YBa_2Cu_3O_<7-delta> (YBCO) are fabricated for changing the physical properties of the superconductors by a doping of the light induced carriers from organic compounds. We have succeeded in the fabrication of the heterostructure, Cu-Pc/YBCO.It is found that when Cu-Pc is deposited on (001) YBCO,the molecular plane of Cu-Pc is parallel to the (001) plane of YBCO.On the other hand, when Cu-Pc is deposited on (001) PrBCO with the same crystal structure as YBCO,the molecular plane is vertical to the substrate plane. The different orientation may originate in the different surface conditions between YBCO and PrBCO.One possible cause is the reduction of the oxygen from the surface of YBCO.The reduction of the normal state resistance were observed for Cu-Pc deposited sample and non-deposited sample. Below T_c onset, the resistance was increased due to the irradiation effect. After the calibration of the temperature, however, it was confirmed that the resistance is decreased by a light irradiation. It was also observed that the resistance is reduced within a wide temperature range for the sample consisting of semiconducting YBCO due to the oxygen reduction. The reduction of the resistance may occur by a pure light activation process because the resistance recovered to the initial value after interrupting the light irradiation. We can not clarify the carrier doping from the Cu-Pc to YBCO becouse the different Tcs' for Cu-Pc deposited sample and non-deposited sample.