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.

铁磷族元素呈现出丰富的相图，其中超导性与自旋密度波（SDW）和向列序共存并竞争，从而产生非常规的配对机制。超导性可以通过载流子掺杂（异价）、施加压力或等价掺杂来获得。尽管人们普遍认为自旋涨落在库珀对的形成中起着重要作用，但诸如磁性的作用、化学调谐的本质以及由此产生的配对对称性等许多方面仍然未知。 SrFe2(As1-xPx)2、(Sr122) 和 LaFeAs1-xPxO (La1111) 是典型的等价掺杂超导体，因为 P 具有与 As 相似的电子配置。因此，预计不会引入额外的电子或空穴。因此，掺杂P对静磁序的抑制比在电子掺杂化合物中观察到的要缓慢得多。 Ba(Fe1-xPx)2As2 中的等价取代已得到充分记录，并在后一个系统中发现了量子临界点 (QCP) 的清晰特征。因此，QCP 需要在另一个等价系统（即 SrFe2(As1-xPx)2）中进行测试。此外，Sr122 和 P 掺杂的 La1111 系统中的超导性质仍然存在争议。该提案的目的是重点关注 122 和 1111 材料的单晶生长，以及使用 X 射线方法、电阻率、磁化率、比热和低温下 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种极好的组合，可以全面地探索 122 和 1111 化合物的物理特性。该研究的中心目标是：（i）利用法兰克福歌德大学物理研究所Cornelius Krellner教授博士实验室的各种设施来合成单晶，例如铁基超导体。对于Sr122，我将使用自熔剂方法；而对于 La1111，将使用 Sn 助焊剂。对于La1111化合物，迄今为止还没有生长出单晶。第 1111 章(ii) 将探讨等价掺杂超导体中的超导性和磁性以及相图。 (iii) 有据可查的是，磷族元素中的能隙对称性因材料而异。此外，实验证实了SC序参数的精确对称性；其与兴奋剂有关的演变仍然存在很大争议。因此，了解超导基态的对称性将为磷族化合物的微观配对机制提供线索，并有助于更深入地理解高温超导现象。