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

在本研究项目中，我们制备了一种新型的异质结材料，它由有机化合物如铜酞菁(CuPc)和高T_c氧化物超导体(如YBa2Cu3O；7-deltaGt；(YBCO))组成，其中的载流子可以在可见光照射下诱导，通过掺杂有机化合物的光生载流子来改变超导体的物理性质。我们成功地制备了异质结CuPc/YBCO，发现当在(001)YBCO上沉积CuPc时，CuPc的分子面平行于YBCO的(001)面，而当在与YBCO晶体结构相同的(001)PrBCO上沉积CuPc时，分子面垂直于衬底平面。不同的取向可能源于YBCO和PrBCO表面条件的不同，一个可能的原因是YBCO表面氧的还原。沉积样品和未沉积样品的正常态电阻都降低了。在T_c开始时，由于辐射效应，抗性增加。然而，在对温度进行校准后，证实了光照射会降低电阻。还观察到，由于氧的还原，由半导体组成的YBCO样品的电阻在较宽的温度范围内降低。由于在中断光照射之后电阻恢复到初始值，因此可以通过纯光激活过程发生电阻的降低。由于沉积的样品和未沉积的样品具有不同的TCS，所以我们不能清楚地说明从Cu-Pc到YBCO的载流子掺杂。

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.