近藤效應在銅氧化物導體傳輸特性之研究

Abstract

本論文研製基於傳統的觀點，銅氧化物超導體中的載子為電洞。然而，Nagaosa 與Lee等人指出，在以spin-charge separation為架構下之 Kondo effect 作用時，當摻雜少量的鋅在銅氧化物中，樣品殘餘電阻會從正比於nimp/p，變化到正比於nimp/(1-p)，當載子濃度從underdoped變化到overdoped， p為載子濃度，nimp為摻雜鋅之濃度。若此結果發生，必定伴隨著顯著的電子結構變化的發生。為了檢驗此重要之論證，我們將研究重點集中於Y0.7Ca0.3Ba2(Cu1-xZnx) 3O7-y (x=0.03,y=0.1~0.6)薄膜之傳輸特性。我們固定鋅之濃度，經由控氧改變載子濃度，探討載子濃度改變所造成的影響，進而研究經摻鋅引起之Kondo screening effect在銅氧化物超導體傳輸特性的影響。實驗結果發現，當載子濃度從underdoped變化到overdoped時，殘餘電阻率對載子濃度的倒數是呈線性的變化關係。意指，無論載子濃度在正常態時如何變化，銅氧化物超導體傳輸之載子仍是電洞。基於此結論，進而探討Nagaosa 與Lee所依據之spin-charge separation理論用於說明underdoped與overdoped伴隨電子結構變化其適用性是有問題的。

A procedure is By 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. To verify this important puzzle, we focus our study on the electric transport properties of Y0.7Ca0.3Ba2(Cu1-xZnx) 3O7-y. The key point is to fix a Zn impruity concentration while the carrier concentration in the sample is changed. In contrast with Nagaosa and Lee’s conclusions, we discovered that r0µnimp/p when carrier concentration is changed from overdoped to underdoped. Our experimental suggest the invalidity of the scenario proposed by Nagaosa and Lee.