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首页> 外文会议>Progress in High-Temperature Superconducting Transistors and Other Devices II >Growth of epitaxial Ba2YCu3O7-delta thin films and control of their superconducting properties
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Growth of epitaxial Ba2YCu3O7-delta thin films and control of their superconducting properties

机译：Ba2YCu3O7-δ外延薄膜的生长及其超导性能的控制

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Abstract: We report on the correlations between structural quality and superconducting behavior in 1000 angstroms thick Ba$-2$/YCu$- 3$/O$-7$MIN$delta$/ (BYCO) films grown on LaAlO$-3$/ (100) from the coevaporation of BaF$-2$/, Y, and Cu, followed by an optimized ex situ annealing process. Epitaxial films with smooth, laminar morphology and excellent crystallinity can be grown to have critical current density (J$-c$/) values nearly identical to single crystals. This finding contrasts with the typical observation that J$-c$/ values in thin films of BYCO are very high compared to those of single crystals. This is attributed to a greater density of flux pinning sites due to structural defects within the films. Our most crystalline films have penetration length $lambda $LSEQ 2000 angstroms. Material disorder of two types can be controlled by the high temperature stage (T$-a$/) of the annealing process. The first type is point defects and dislocations the same size or smaller than the coherence length $xi$-ab$/, which, Rutherford backscattering/channeling suggests, decrease in number with increasing T$-a$/. The second is crevices, pinholes, and microcracks which are at least one to two orders of magnitude larger than $xi$-ab$/. At T$-a$/ $LS 850$DGR@C, crevices, which create areas of nonuniform thickness, occur due to incomplete epitaxial growth and correlate with the presence of weak links. Hence film resistivity is high, T$-c$/ is low, and $lambda is large. As T$-a$/ is increased, the film morphology becomes smoother and all electrical properties improve, except for J$-c$/ in nonzero applied magnetic fields, since the improved epitaxy correlates with reduced flux pinning. By T$-a$/ $EQ 900$DGR@, the BYCO films are similar to single crystals in both cation alignment and J$-c$/ behavior. Above this annealing temperature, pinholes and microcracks develop and increase in both size and density with increasing T$-a$/. Although these relatively large defects do not act as weak links, they do affect magnetic screening (and hence $lambda@).!21s
机译：摘要：我们报道了在LaAlO $ -3 $上生长的1000埃厚Ba $ -2 $ / YCu $ -3 $ / O $ -7 $ MIN $ delta $ /（BYCO）膜的结构质量与超导行为之间的相关性。 （100）由BaF $ -2 $，Y和Cu的共蒸发形成，然后是优化的非原位退火工艺。可以生长具有光滑，层状形态和出色结晶度的外延膜，使其临界电流密度（J $ -c $ /）值几乎与单晶相同。这一发现与典型的观察结果形成了鲜明的对比，即与单晶晶体相比，BYCO薄膜中的J $ -c $ /值非常高。这归因于由于膜内的结构缺陷而导致的助焊剂钉扎位点的密度更大。我们最结晶的薄膜的穿透长度为$λλLSEQ2000埃。可以通过退火过程的高温阶段（T $ -a $ /）控制两种类型的材料无序。第一种是点缺陷和位错，其大小等于或小于相干长度$ xi-ab $ /，卢瑟福反向散射/通道表明，随着T $ -a $ /的增加，数量减少。第二个是缝隙，针孔和微裂纹，它们至少比$ xi $ -ab $ /大一到两个数量级。在T $ -a $ / $ LS 850 $ DGR @ C处，由于不完全的外延生长而产生了产生厚度不均匀区域的缝隙，并且与薄弱环节有关。因此，膜电阻率高，T $ -c $ /低，而λλ大。随着T $ -a $ /的增加，薄膜形态变得更平滑，并且所有电性能都得到改善，但在非零磁场中的J $ -c $ /除外，因为外延的改善与磁通钉扎的减少有关。通过T $ -a $ / $ EQ 900 $ DGR @，BYCO膜在阳离子排列和行为方面都类似于单晶。在此退火温度以上，针孔和微裂纹会随着T $ -a $ /的增加而发展，并且尺寸和密度也会增加。尽管这些相对较大的缺陷不会充当薄弱环节，但它们确实会影响磁屏蔽（并因此影响$ lambda @）。21s

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