Crystal growth and thermodynamic investigations in isovalently doped iron-based superconductor

等价掺杂铁基超导体的晶体生长和热力学研究

• 批准号: 278038270
• 负责人: Dr. Mahmoud Rabie Abdel-Hafez, Ph.D.
• 金额: --
• 依托单位: Lyman Laboratory of Physics
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/278038270?language=en
• 关键词: Crystal; growth; thermodynamic; investigations; isovalently

Iron pnictides present a rich phase diagram wherein superconductivity coexists and competes with the Spin Density Wave (SDW) and nematic order, resulting in unconventional pairing mechanisms. Superconductivity can be obtained through carrier doping (heterovalent), the application of pressure, or isovalent doping. Although there is a general consensus that spin fluctuations play an important role in the formation of Cooper pairs, much aspects such as the role of magnetism, the nature of chemical tuning, and the resultant pairing symmetry remain unknown. SrFe2(As1-xPx)2, (Sr122) and LaFeAs1-xPxO (La1111) are prototypical isovalently doped superconductors, as P has a similar electronic configuration to that of As. Therefore, it is not expected to introduce extra electrons or holes. Hence, doping P suppresses a static magnetic order much more gradually than observed in electron doped compounds. Isovalent substitution has been well documented in Ba(Fe1-xPx)2As2 with clear signatures of a Quantum Critical Point (QCP) found in the latter system. Thus, the QCP needs to be tested in another isovalent system i.e., SrFe2(As1-xPx)2. In addition, the nature of superconductivity in Sr122 and in La1111 systems with P doping remains under debate. The aim of this proposal is to focus on the single crystal growth of 122 and 1111 materials, together with a thorough characterization of crystals using x-ray methods, resistivity, magnetic-susceptibility, specific-heat, and Muon Spin Resonance measurements at low temperatures, to gain insights into the questions raised above. To use crystal growth and physical characterization in one laboratory provides an excellent combination to explore the physics of the 122 and 1111 compounds in a comprehensive way. Central objects of the research are: (i) To use diverse facilities in the laboratory of Prof. Dr. Cornelius Krellner at the Physics Institute at the Goethe University Frankfurt to synthesize single crystals such as Fe-based superconductors. For Sr122, I will use a self-flux method; whereas for La1111, the Sn-flux will be employed. For La1111 compounds, so far no single crystals have been grown. But learning to grow these single crystals of the 1111 systems will be of great scientific interest to better understand the physics behind various 1111 compounds. (ii) Superconductivity and magnetism in isovalently doped superconductors as well phase diagrams will be explored. (iii) It is well documented that the gap symmetry in pnictides differs from material to material. Moreover, experimental confirmations of the precise symmetry of the SC order parameter; as well its evolution with doping remains highly controversial. Therefore, understanding the symmetry character of SC ground states should provide clues to microscopic pairing mechanisms in pnictides and will give a deeper understanding of the phenomenon of high-temperature superconductivity.

铁磷属化合物呈现出丰富的相图，其中超导性与自旋密度波（SDW）和超有序共存并竞争，导致非常规的配对机制。超导电性可以通过载体掺杂（异价），施加压力或等价掺杂来获得。虽然人们普遍认为自旋涨落在库珀对的形成中起着重要作用，但许多方面，如磁性的作用，化学调谐的性质，以及由此产生的配对对称性仍然未知。SrFe_2（As_（1-x）Px）_2（Sr_（122））和LaFe_（1-x）P_xO（La_（1111））是典型的等离子体掺杂超导体，因为P具有与As相似的电子组态。因此，预计不会引入额外的电子或空穴。因此，掺杂P抑制静态磁序比在电子掺杂化合物中观察到的要缓慢得多。在Ba（Fe 1-xPx）2As 2中已经很好地记录了等价取代，在后者系统中发现了量子临界点（QCP）的明确特征。因此，QCP需要在另一个等价系统中进行测试，即，SrFe 2（As 1-xPx）2.此外，在Sr 122和La 1111系统中的P掺杂的超导电性的性质仍然存在争议。该提案的目的是专注于122和1111材料的单晶生长，以及在低温下使用X射线方法，电阻率，磁化率，比热和μ子自旋共振测量对晶体进行全面表征，以深入了解上述问题。在一个实验室中使用晶体生长和物理表征提供了一个很好的组合，以全面的方式探索122和1111化合物的物理性质。研究的主要目标是：（一）利用法兰克福歌德大学物理研究所Cornelius Krellner教授实验室的各种设施，合成铁基超导体等单晶。对于Sr 122，我将使用自熔剂法;而对于La 1111，将使用Sn熔剂。对于La 1111化合物，迄今为止还没有生长出单晶。但是，学习生长这些1111系统的单晶将具有巨大的科学兴趣，可以更好地理解各种1111化合物背后的物理学。(ii)本课程将探讨掺有异方晶系之超导体之超导电性与磁性，以及相图. (iii)有充分的文献证明，磷属元素化物中的差距对称性因材料而异。此外，SC序参量精确对称性的实验证实;以及其随掺杂的演变仍然存在很大争议。因此，了解SC基态的对称性特征，将提供线索的微观pnictides的配对机制，并会给高温超导现象的更深入的理解。