| With the progress of high-quality epitaxial thin film preparation technology,the research on oxide interface superconductivity has developed rapidly in the past 20 years.It is of great value in studying the interface physics related to the coexistence and competition of multiple quantum orders,understanding the mechanism of hightemperature superconductivity,and developing new oxide electronic devices that surpass the traditional silicon-based semiconductor devices.In this thesis,two kinds of oxide interface systems were studied.One is KTaO3 interface superconducting system.The recently discovered KTaO3 interface superconducting systems(EuO/KTaO3,amorphous LaAlO3/KTaO3,etc.)have a superconducting transition temperature one order of magnitude higher than that of the traditional SrTiO3 interface system,and are affected by the crystal orientation on the surface of KTaO3,which has attracted extensive attention.The second is the copper oxide interface system.Copper oxide is the most classical high-temperature superconducting system,and it is of great practical importance to explore new interface high temperature superconductivity.The content of this paper is arranged as follows:Firstly,the background of SrTiO3,KTaO3 and copper oxide interface(conductive)superconducting system is introduced,and then the basis for selecting the topic is given.Secondly,the technical methods of thin film preparation(pulsed laser deposition and electron beam evaporation),nanofabrication technologies,morphology and structure characterization,electrical transport measurements,and ionic liquid gating used in this thesis are presented.Then,in order to study the mechanism of KTaO3 interface superconductivity,we used ionic liquid electronic double layer transistor to regulate KTaO3 single crystal,realized electron doping on KTaO3(001),(110)and(111)crystal planes,and obtained 2D superconductivity with transition temperatures of 2 K and 1 K on KTaO3(111)and(110)surfaces,respectively.In contrast,the KTaO3(001)sample showed no sign of superconductivity until the lowest temperature of 0.4 K.The thickness and coherent length of the superconducting layer on the surface of KTaO3(111)and(110)controlled by ionic liquid were obtained by measuring the upper critical magnetic field in the vertical and parallel directions.It was found that the coherent length was equivalent to the KTaO3 interface superconductivity,and the thickness of the superconducting layer was larger than that of the KTaO3 interface superconductivity.By studying the effects of different gate voltages and the comparison of reference electrodes,we believe that the regulation of KTaO3 by ionic liquids may be a mixed effect of electrostatic and electrochemical.This work not only shows that the key factor of KTaO3 interface superconductivity is the electron doped KTaO3 surface,but also paves the way for studying the intrinsic superconductivity of KTaO3 by using ionic liquid electronic double layer transistor technology.Finally,in order to search for new interfacial high-temperature superconducting systems,we started from the classical copper oxide La2CuO4 and found hightemperature superconductivity at the interface consisting of two Mott insulators,PrBa2Cu3O7 and La2CuO4,for the first time.In this work,we used pulsed laser deposition system to construct PrBa2Cu3O7/La2CuO4 heterostructure samples and found high-temperature superconductivity at the interface;in contrast,both La2CuO4 and PrBa2Cu3O7 single-phase films grown under the same conditions are Mott insulators.By controlling the oxidation conditions and selectively doping a specific CuO2 surface with Fe(Fe can suppress superconductivity),it was found that superconductivity occurs on the La2CuO4 side near the interface and can be confined to no more than two layers of unit cells(about 2.6 nm).Based on the experimental data,we suggest that the mechanism of high-temperature superconductivity at the PrBa2Cu3O7/La2CuO4 interface is the redistribution of oxygen at the interface. |
