异质多层高温超导薄膜的研究

由高温超导和绝缘体、半导体、磁性体等材料构成的异质结具有一系列独特的物理性能，不仅有助于人们深入了解高温超导的一些物理参数，也可促进其在微电子领域的应用。该研究则拟将具有不同临界温度Tc的两种高温超导材料，如YBCO和BSCCO按照共格方式交替叠层生长，使其形成由高温超材料组成异质结（2层）、约瑟夫森结（3层）、甚至超晶格（多层）。这样，当温度变化时，所制备的多层膜体系会处于不同的物理状态，以异质结为例，在常温时，类似于普通的半导体异质结，当温度处于两个临界温度Tc之间时，类似于肖特基结，当两相均处于超导态时，就会形成全超导异质结。如果选择合适的晶格匹配，在不失去超导电性的同时，两相共格界面会保持一定的弹性应力，从而在两层之间形成原子尺度的势垒层，有望解决高温超导相干长度短、制备约瑟夫森结难的问题。进一步研究两相超导材料的界面特性，载流子的输运特性、光伏特性等都具有一定的学术意义及应用价值

Heterojunctions of high-temperature superconductor (HTS)/insulating oxide, HTS/semiconductor or HTS/ magnetism usually exhibit a series of unique physical properties, which is not only helpful for us to understand some physical parameters of HTS but also can promote their future special application in the field of microelectronics. In this project, a novel heterostructure with coherent alternating layers will be prepared by using two kinds of HTS materials, YBCO and BSCCO, with different critical transition temperature Tc. When the number of alternating layers is two, three and even more, the corresponding multilayer heterostructures are called as HTS heterojunction, Josephson junction and superlattice, respectively. Thus, with the change of temperature, the as prepared multilayer heterostructure will display the different physical properties. Take the bilayer HTS heterostructure as an example, the heterostructure will exhibit a common characteristic like semiconductor heterojunction when the temperature is higher than the Tc of the two HTS films; while it will be a superconducting heterojunction when the temperature is lower than the Tc of the two HTS films. Besides, it will exhibit the characteristics of Schottky junction when the temperature is between the two Tc. The appropriate lattice mismatch between two superconducting phases will induce a certain elastic stress in the coherent interface of them without the loss of superconductivity, which maybe leads to the formation of barrier between the interface atoms. It is expected to overcome the difficulties in the preparation of high temperature superconducting Joseph junction due to their short coherence length. In addition, it is quite significant for the academic research and practical application to investigate the interfacial properties of the two superconducting materials, their transport characteristics of charge carrier and photovoltaic characteristics.