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arXiv 0706.0214cond-mat.supr-concond-mat.str-el
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高温超导体Bi2Sr2CaCu2O8 +d中电子对形成的原子尺度可视化

Visualizing pair formation on the atomic scale in the high-Tc superconductor Bi2Sr2CaCu2O8+d

Kenjiro K. Gomes, Abhay N. Pasupathy, Aakash Pushp, Shimpei Ono, Yoichi Ando, Ali Yazdani

摘要:

传统超导体中的电子配对发生在超导转变温度Tc,在电子态密度(DOS)中产生能隙D。在高温超导体中,在高于Tc的温度范围内,DOS中存在部分能隙。一个关键的问题是,在DOS以上的Tc的差距是否与配对,是什么决定了温度在不相干对的形式。在这里,我们报告的第一个空间分辨测量间隙形成的高Tc超导体,测量Bi 2Sr 2CaCu 2 O 8 +d样品具有不同的Tc值(空穴浓度为0.12至0.22),使用扫描隧道显微镜。在从0.16到0.22的掺杂范围内,我们发现配对间隙在Tc以上的纳米级区域中成核。这些区域随着温度的降低而扩散,导致超导状态下间隙尺寸的空间分布。尽管不均匀性,我们发现,每一个配对间隙的发展在温度Tp本地,以下的关系2D/kBTp = 8。在非常低的掺杂(<0.14)下,DOS的系统性变化表明存在另一种现象,该现象与电子配对无关,并且可能与电子配对竞争。我们对纳米级配对区域的观察为理解最近报道的空穴掺杂高Tc氧化铜超导体中Tc以上的波动超导响应提供了缺少的微观基础。

英文摘要:

Pairing of electrons in conventional superconductors occurs at the superconducting transition temperature Tc, creating an energy gap D in the electronic density of states (DOS). In the high-Tc superconductors, a partial gap in the DOS exists for a range of temperatures above Tc. A key question is whether the gap in the DOS above Tc is associated with pairing, and what determines the temperature at which incoherent pairs form. Here we report the first spatially resolved measurements of gap formation in a high-Tc superconductor, measured on Bi2Sr2CaCu2O8+d samples with different Tc values (hole concentration of 0.12 to 0.22) using scanning tunnelling microscopy. Over a wide range of doping from 0.16 to 0.22 we find that pairing gaps nucleate in nanoscale regions above Tc. These regions proliferate as the temperature is lowered, resulting in a spatial distribution of gap sizes in the superconducting state. Despite the inhomogeneity, we find that every pairing gap develops locally at a temperature Tp, following the relation 2D/kBTp = 8. At very low doping (<0.14), systematic changes in the DOS indicate the presence of another phenomenon, which is unrelated and perhaps competes with electron pairing. Our observation of nanometre-sized pairing regions provides the missing microscopic basis for understanding recent reports of fluctuating superconducting response above Tc in hole-doped high-Tc copper oxide superconductors.

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