YBa2Cu3O7與SrMnO3 異質結構之 電荷轉移與特性量測

Abstract

本論文藉由脈衝雷射鍍膜(Pulse Laser Deposition，PLD)的技術製作反鐵磁(antiferromagnetic)材料SrMnO3(SMO)與高溫超導(Superconducting)材料YBa2Cu3O7-x(YBCO) 之雙層薄膜異質介面結構並研究其特性。研究中分為兩部分:一種為將SMO放至上層YBCO為下層的(AS)系統；以及YBCO在上層SMO在下層的(SA)系統。利用同步輻射中心X光近緣吸光譜(XANES)及電子能譜分析儀(X-ray Photoelectron Spectroscopy, XPS)搭配電性及磁性量測，在SA系統中，其電性量測發現在此系統中會有Insulator Superconductivity transition現象，並且隨著增加SMO之厚度，此現象更為明顯，而其原因是因為電荷轉移，將原本具有超導性的YBCO轉變成絕緣性的YBCO。而在AS系統中，隨著增加YBCO之厚度，其Mn之價數也隨之提高，伴隨著其電性也更趨近於導體。

The electrical and magnetic properties of two epitaxial heterostructures of the anti-ferromagnetic SrMnO3 (SMO) layer / high-temperature superconductor YBa2Cu3O7-x (YBCO) layer were studied in the thesis. One structure is YBCO-on-SMO system (SA) and the other is SMO-on-YBCO system (AS). In the SA system, we found that the superconductor-to-insulator transition (SIT) occurs with an increasing in the thickness of SMO layer. The cause of SIT is charge transfer between the YBCO (SC)/ SMO (I) interface. In the AS system, increasing the thickness of YBCO results in higher valence states of Mn ions in SMO layer. The charge transfer between the AS interface was also observed using X-ray Absorption Spectroscopy (XAS) measurement. Furthermore, XPS measurements suggest that conductivity of SMO layer becomes higher with an increase in the thickness of YBCO layer .