摻鈣高溫超導釔鋇銅氧的近吸收邊緣X光吸收光譜之研究

Abstract

本次研究採取高溫超導材料YBa2Cu3Oy（YBCO）的薄膜系統，摻入不同含量的鈣Ca，與控制其氧含量，得到Y1-x CaxBa2Cu3Oy（鈣含量x = 0.0、0.1、0.2、0.3與氧含量y=6.1、6.5、6.9）等等的樣品。以台灣同步輻射中心的6m HSGM光束線進行近吸收邊緣x光吸收光譜實驗（XANES），研究其載子分佈對於高溫超導的機制影響。 實驗的結論為：不論摻鈣或是提高氧含量，都是增加電洞的行為。摻入鈣所增加的電洞，幾乎只加在銅氧平面（CuO2 plane）上，對於銅氧鍊或軸向氧（apical O(4)）的影響不大。提高氧含量所增加的電洞，對於銅氧平面（CuO2 plane)、銅氧鍊（CuO3 chain)及軸向氧（apical O(4))，都有明顯的效應。影響Tc的最大因數是銅氧平面上的載子數。

Using polarization-dependent O 1s and Cu 2p near-edge x-ray absorption structure on Y1-xCaxBa2Cu3Oy thin films, we have identified the unoccupied electronic states of the samples and studied the dependence on Ca concentration. X-ray absorption structure (XANES) was recorded by fluorescence yield mode, which is a bulk-sensitive technique. XANES can give information about the carrier concentration n on specific sites. Results: Both of Ca and Oxygen doping increase hole numbers. With Ca doping, the induced holes almost increase on plane instead of chain or apical O（4）site. Only the O(1) on the CuO3 chain was taken away, when the sample is oxygen–depleted. The carriers concentration on the CuO2 plain play the major role, that affects the critical temperature Tc.