基于铁基超导单晶器件的超导向列态研究

Fe-based superconductors was the most important progress on the researches of high transition temperature superconductors after the discovery of Cu-based superconductors, nevertheless, it is essential to understand the superconducting mechanism. Recently, the electronic nematic state was gradually considered as one of essential topic to explore the superconducting mechanism, and most of these studies are focused around the normal state after the structure transition or antiferromagnetic order transition. However, it is still an open question if another electronic order will be induced as the existence of superconductivity, such nematic state should be related to the superconductivity directly. In the conversional methods, the bulk crystals was applied to measure the nematic state, which cannot be used to measure the superconducting transport properties. In this project, we plan to research on the nematic state under superconductivity and the corresponding superconducting mechanism, via to the functional micro-devices from Fe-based superconductors, the detailed process is as following: fabricate the micro-devices with the angular electrodes and mesa structure，to avoid the problem in bulk crystal; study on in-plane and out-of-plane anisotropic magnetoresistivity and upper critical fields, via to the static and pulsed high magnetic fields technique; research on the under-, optimal, and over-doped 11- and 122-system superconductors, to complete the distribution of nematic state on the superconducting phase diagram; analysis the mechanism of superconducting nematic state, and explore the relation with the high temperature superconducting mechanism. The implementing on this project will provide experimental supporting on the analysis of basic physical properties by applying superconducting devices.

铁基高温超导是继铜基之后超导领域最重要的研究进展，但其最核心的超导机制问题还亟待研究。电子结构向列态已被认为是探索超导机制的重要领域，现有研究集中在正常态下结构相变或磁有序转变之后，而超导转变是否也会诱发向列态序还没有报道，该向列态应与超导配对机制关联。常规的向列态测试采用块体单晶，但无法满足超导态下输运特性精确表征的要求。本项目中，我们拟制备具有功能特性的铁基超导器件来研究超导态下的向列态与超导配对机制的前沿问题：采用环状电极和平台等微结构超导器件为研究对象，避免块体样品的局限性；以稳态磁场和脉冲强磁场为抑制超导的研究手段，研究面内、面外各向异性磁阻和上临界磁场；研究11-体系和122-体系超导的欠、最佳和过掺杂体系，以完善超导相图中向列态分布；分析超导向列态形成机制以及与高温超导机制之间内在关联。本项目顺利实施将为超导器件应用于基础物性研究提供实验依据。

高温超导技术被认为是21世纪最重要潜在突破技术之一，目前已经经过了三十多年的长足发展，但是目前还面临几个关键性的基础问题亟待解决。2008年，随着另一个高温超导家族，即铁基高温超导体的发现，并迅速成为了目前超导科学研究中的前沿领域。铁基超导的母体相在低温下具有反铁磁序、电荷密度波、电子结构序、以及晶格结构转变等相变。随着掺杂的增加，这些序逐渐被抑制，超导随之出现，因此被直观地认为这些有序态是超导的起源。本项目主要任务是以铁基超导单晶器件为研究对象，探索铁基超导体在超导态以下的向列态现象及其形成机制。具体完成了以下研究内容：1）采用原位制备和微加工技术，克服单晶器件界面退化和氧化问题；2）开发作为面内、面外各向异性磁阻和上临界磁场的功能特性的超导器件；3）在稳态磁场下，实现面内、面外各向异性磁阻和上临界磁场的可控表征；4）采用脉冲强磁场抑制超导电性，探索远离超导温度以下的各向异性，从而研究超导态下的向列态序；5）基于多带模型，分析超导向列态的引起机制和超导机制之间内在关联。本项目顺利实施将为超导器件应用于基础物性研究提供实验依据。