JULY 14, 2018 —

New work from A group of scientists led by Dr. Yang Ding of HPSTAR, provided the first experimental evidence of lattice inhomogeneity in high-temperature superconductors and found that the structural inhomogeneity correlates well with superconductivity in single-crystal Bi-2212—bismuth-based cuprate (Bi2Sr2CaCu2O8+δ) at high pressure. This study is published in the Journal of Physical Chemistry Letters.

Inhomogeneities in superconductors that had long been noticed but left unexplained, which could affect or alter the superconducting transition temperature (Tc). However, big challenges remain in building the connection between lattice inhomogeneity and superconductivity.

Dr. Jianbo Zhang, the lead author of the paper, together with his colleagues apply imaging and small-angle scattering measurements on single crystal Bi-2212, revealing structural inhomogeneity called “ribbon phase”.

“The ribbon phase is the direct evidence of lattice inhomogeneity in Bi-2212. The lattice inhomogeneity is very challenging to detect, since the x-ray diffraction peaks from the ribbon phase are entirely overlapped with the diffraction peaks from the modulated structure of the Bi-2212 crystal”, said Dr. Jianbo Zhang.

“This is the main reason why previous studies failed to find the ribbon phase even with many years of efforts. We also have tried various synchrotron techniques, from high-energy diffraction, anomalous scattering, to Laue nano-imaging, yet all of which failed to disclose the ribbon phase”, Dr. Yang Ding added. “We have finally used monochromatic nano-imaging measurements to successfully discover it”.

Their further study show that the changes of the ribbon phase’s morphology closely tied to the doom-shaped TC at high pressure. What’s more, their later x-ray absorption, inelastic scattering, and irradiation experiments indicate that the Tc also correlated with the inhomogeneous distribution of oxygen holes.

“These findings provide a direct link between TC and inhomogeneity in cuprate Bi-2212”, said Dr. Yang Ding. “We believe that inhomogeneity is general among high-temperature superconductors and synchrotron nanoprobe could be a powerful tool to do such investigations”.

Caption：The morphology of the ribbon-like phase changes at two different stages and the TC pressure evolution.

媒体报道：

中国科学报：http://news.sciencenet.cn/htmlnews/2018/7/415838.shtm

知社学术圈： https://baijiahao.baidu.com/s?id=1607739292492604516&wfr=spider&for=pc

研究高温超导（HTSC）的一个挑战是缺乏直接的实验证据，证明晶格的非均匀性对超导电性的影响。北京高压科学研究中心的丁阳团队借助一系列的同步辐射技术结合电输运测量，来揭示晶格的非均匀性和超导电性之间的关系。通过使用硬x射线纳米成像和小角度散射技术，发现在最佳掺杂的Bi-2212中存在一个微米尺度的带状相。在压力下，带状相形态的演化与拱形的超导转变温度-TC变化行为密切关联。同时x射线吸收研究表明，在CuO平面内，TC的增加与氧空穴的再分配有关，而当氧空穴变得不动时，TC伴随压力开始减少。额外的x射线辐照实验表明，辐射引起的纳米级的氧空穴的短程排序也可以进一步降低TC，这表明最优的TC不仅受到了带状相形态的影响，而且还受到了氧空穴分布的影响。该研究首次提供了令人信服的实验证据，并揭示出TC与微米与纳米级的不均匀性密切关联。