Superconductivity and influence of the interface on the normal-state resistance of ultrathin YBa_2Cu_3O_(7-δ) film

摘要

The high-T_C oxide superconductors are of high anisotropy due to their layered crystalline structure. For example, the anisotropic factor of YBa_2Cu_3O_(7-δ) (YBCO) is about 20, while that of TlBaCaCuO reaches to 10~4. The dimensionality associated with the anisotropy is one of the important factors to determine the superconductivity, flux pinning and flux motion feature of these materials. So the investigation of coupling between CuO_2 planes (dimensionality) is very helpful for understanding the novel physical phenomena which are not found in the conventional superconductors. The superconducting multilayers separated by non-superconducting layer have been studied, in which the minimun thickness of superconducting layer is down to one-unit-cell. In order to study the growth mechanism of the initial growth stage of high-T_C thin film and to explore the minimum unit of the high-T_C superconductivity, extensive attention has been paid to high-T_C ultrathin film. Due to the difficulty of making well-characterized specimens and the reliability of measurements, it is still necessary to investigate the ultrathin film. Also, the ultrathin YBCO film is important for some superconducting electronic devices, for example, the superconducting electrical field effect device. Recently, we prepared a series of YBCO ultrathin films. In this note, the superconductivity and the influence of the interface on the normal-state of resistance two-unit-cells (2.5 nm)-thick YBCO ultrathin film are discussed.