摻雜電洞在銅氧化物超導體的電子結構之研究

Abstract

銅氧化物超導體的載子，廣泛的被認為是電洞。但是Nagaosa和Lee以spin-charge separation為架構下之Kondo effect作用時，認為當鋅掺入在銅氧化物中，當載子濃度從underdoped到overdoped時，樣品殘餘電阻會從正比於nimp/p，變化到正比於nimp/(1-p)載子會從電洞變成電子，暗示銅氧化物的電子結構將會被改變。而最近的研究中，X.J.Zhou 用角分辨光電子發射能譜(ARPMS)去研究La2-xSrxCuO4 (LSCO)單晶費密面的變化，發現載子濃度大於0.22時，銅氧化物的載子才會變成電洞，這結果與前者有很大的差異。另外，Ando應用電阻率曲率繪圖的方法，繪製出另一類型的銅氧化物相圖，使得更方便去探討一些超導相圗上的傳輸特性，我們也將用同樣的方法去繪製並探討Y0.7Ca0.3Ba2Cu3O7-y的相圗。為了檢驗此重要之論證，我們將研究重點集中於Y0.7Ca0.3Ba2Cu3O7-y和Y0.7Ca0.3Ba2(Cu1-xZnx)3O7-y (x = 0.01、0.03)薄膜之傳輸特性。我們延續先前鍾佩君的實驗，以固定鋅的含量量測殘餘電阻隨著載子濃度從underdoped到overdoped的改變，從原本只到p = 0.11延伸作到p = 0.08，從樣品傳輸特性上的變化，印證銅氧化物的電子結構，傳導載子依然仍是電洞。

By the conventional point of view, the prominent carriers in cuprates are holes. However, Nagaosa and Lee claimed that the residual resistivity was in the form of r0µnimp/p in the underdoped regime and r0µnimp/(1-p)in the overdoped regime for Zn-doped cuprates with the Kondo screening effect in the spin-charge separation context. Here nimp is the Zn impurity concentration and p the hole concentration. If this case is true, a novel change of the electronic structure would happen from underdoped to overdoped regime. Recently, X.J. Zhou using angle-resolved photoemission spectroscopy (ARPMS) to observation of a change in Fermi-surface of (La2-xSrx)CuO4 with doping. When x = 0.22, the Fermi-surface will be changed from hole-like to electron-like. It’s different from former result. Otherwise, Ando made resistivity curvature mapping (RCM) to draw other type electric phase diagram of cuprates. It is conveniently to discussion the electronic transport properties of the curpates. We also try to use the same method to investigat and draw the pahse diagram of Y0.7Ca0.3Ba2Cu3O7-y. We focus our study on the electric transport properties of Y0.7Ca0.3Ba2Cu3O7-y & Y0.7Ca0.3Ba2(Cu1-xZn0x) 3O7-y (x = 0.01、0.03)thin films. The key point is to fix the Zn doping level while the carrier concentration in the sample is changed. To continuous P. C. Chung’s experiments, we pushed the hole concentration from 0.21 to 0.08, further. The evolution of the electronic structure with hole doping inferred from the changes of the transport properties is explored.