我們製作了不同m, N的 [(YBa2Cu3O7-δ)m/(Y0.7Ca0.3Ba2Cu3O7-δ)m]N多層膜並研究這些過摻雜 (overdoped) 多層膜在磁場下的傳輸性質。當δ ∼ 0.05 時， YBa2Cu3O7-δ 為最佳摻雜(optimum doped)，所以僅改變氧含量幾乎不可能使 YBa2Cu3O7-δ 成為過摻雜態。將 Pr3+ 以 Ca2+ 取代將使該處晶胞 (unit cell) 增加一個電洞並增加 123 系統的摻雜程度 (doping level)。 Y0.7Ca0.3Ba2Cu3O7-δ 在一大氣壓氧氣下經過退火補氧後臨界溫度及電阻率都下降，證實了 Y0.7Ca0.3Ba2Cu3O7-δ 是過摻雜態。
所有的薄膜都是由脈衝雷射濺鍍同組成的靶材所製成。X光圖形並無任何衛星峰 (satellite peak) 結構。我們量測了這些樣品在磁場下電阻率對溫度的變化 (r-T) 及 Hall 效應。室溫下 Y0.7Ca0.3Ba2Cu3O7-δ 薄膜的自由載子濃度最低，但電導度最高。所有的樣品中 Y0.7Ca0.3Ba2Cu3O7-δ 薄膜的反轉 Hall 訊號最難被磁場所壓制，而且 Hall 係數變號二次。
我們推測鈣的擴散造成層與層間介面的模糊，因此無衛星峰出現。當磁場平行薄膜表面時，樣品 5/5 的電阻相變轉變寬度的增加量最小，意味著五層YBa2Cu3O7-δ 的厚度已大於二倍鈣的擴散長度。 Y0.7Ca0.3Ba2Cu3O7-δ 異常低的自由載子濃度可能導因於自由電子的產生而抵消了部份 Hall 電壓或是電洞的等效質量有所改變。我們認為 Hall 係數的二次變號現象是因為薄膜局部的臨界溫度隨著位置而改變及量測系統的溫度誤差所造成。

We fabricate [(YBa2Cu3O7-δ)m/(Y0.7Ca0.3Ba2Cu3O7-δ)m]N multilayers with different combinations of (m,N) and study their transport properties in overdoped region under magnetic field. YBa2Cu3O7-δ reaches optimum doping with δ ∼ 0.05, indicating that YBa2Cu3O7-δ system can hardly evolve into overdoped region by merely altering their oxygen content. Replacing Pr3+ with Ca2+ increases one hole of the unit cell where substitution occurs and substantially doping level of 123 system. The decrease of both Tc and resistivity after annealing under 1 atm O2 proves that Y0.7Ca0.3Ba2Cu3O7-δ is overdoped.
All the films are deposited by pulse laser deposition with stoichiometric targets. X-ray patterns of those multiplayers do not show any satellite peaks. We measure R-T under magnetic field and Hall effect. Sample 5/5 under magnetic field along a-b plane has smallest broadening of r-T. At room temperature Y0.7Ca0.3Ba2Cu3O7-δ single layer has smallest carrier concentration but largest conductivity. The sign reversal Hall signal of Y0.7Ca0.3Ba2Cu3O7-δ is the hardest to suppress by magnetic field among all the samples. Y0.7Ca0.3Ba2Cu3O7-δ has double sign reversal of Hall coefficient.
We conjecture that the Ca diffusion blurs the interfaces between the layers and thus eliminates the satellite peaks. The smallest broadening of sample 5/5 implies that the thickness of 5 unit cell of YBa2Cu3O7-δ layer is longer than twice of the Ca diffusion length. The abnormally small carrier concentration of Y0.7Ca0.3Ba2Cu3O7-δ may be attributed to the coexistence of mobile holes and electrons or the variation of effective mass of holes. We argue that the double sign reversal is due to the inhomogeneous Tc distribution on the film and the temperature error.

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