Magnetism, nematicity and superconductivity in 1111 oxypnictide single-crystals

1111氧磷元素单晶的磁性、向列性和超导性

• 批准号: 461247437
• 负责人: Professor Dr. Markus Braden
• 金额: --
• 依托单位: Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden (IFW) e.V.
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/461247437?language=en
• 关键词: Magnetism; nematicity; superconductivity; 1111; oxypnictide

The discovery of superconductivity in F-doped LaFeAsO polycrystals initiated the so-called iron-age of high-temperature superconductivity. These materials are frequently referred to as Fe-based superconductors (IBS). Three types of order manifest in the low-temperature phases of IBS: (i) orbital or electronic ordering (ii) orthorhombic distortion, and (iii) the antiferromagnetic spin density wave order. Precedent to long-range ordered states, a phase with broken rotational symmetry but with preserved time-reversal and translation symmetries emerges and is referred to as nematic state. Magnetism, nematicity and superconductivity are intimately interwoven but the question, which of these three orderings is central, remains matter of controversy. While there have been comprehensive studies on many families of IBS, the initial system of doped REFeAsO (1111) compounds with RE a rare earth has been very little studied due to the absence of suitable single crystals. This lack of understanding the 1111 system is highly regrettable, as these compounds exhibit the highest bulk superconducting transition temperatures, and as there are significant differences with the other classes such as a higher degree of orbital degeneracy and a reduced electronic dispersion perpendicular to the layers.A deep understanding of IBS in general and of 1111 materials in particular requires single crystals of appropriate size, quality and composition. Due to the major challenges in crystal growth, the 1111 family is currently the least understood among all IBS. Only recently, large and well faceted LaFeAsO single crystals with considerable c axis growth were grown in the group of PI Wurmehl at the IFW in Dresden using solid-state single-crystal growth. This approach is not commonly known and not fully understood, the growth is diffusion controlled and crystals are grown from a polycrystalline matrix via abnormal grain growth. This success in growing LaFeAsO crystals will set the stage for exciting experiments both in the field of chemistry and physics. We wish to profit of the opportunities the first availability of the 1111 crystals offers by combining the crystal growth efforts with scattering studies using X-ray and neutron radiation. Thereby we want to clarify the crystal structure and in particular to search for the structural distortions evidenced by NQR experiments. We will characterize magnetic order and short-range magnetic correlations as function of composition, temperature and uniaxial strain. Magnetic excitations are considered as a key element of the superconducting pairing and can be studied by inelastic neutron scattering when larger amounts of crystals become available. It seems most interesting to study the superconducting spin-resonance modes in materials with higher transition temperatures and to study the spin-space anisotropies in 1111 materials, which exhibit a different electronic structure.

掺F的LaFeAsO多晶超导性的发现，开启了高温超导的铁时代。这些材料通常被称为铁基超导体（IBS）。三种类型的秩序表现在低温阶段的IBS：（i）轨道或电子有序（ii）正交畸变，和（iii）反铁磁自旋密度波秩序。在长程有序态之前，出现了一种旋转对称性被破坏但保留了时间反演和平移对称性的相，称为自旋态。磁性、向列性和超导性是紧密交织在一起的，但这三种有序性中哪一种是中心的问题仍然存在争议。虽然已经对IBS的许多家族进行了全面的研究，但由于缺乏合适的单晶，对RE（稀土）掺杂REFeAsO（1111）化合物的初始系统的研究很少。这种对1111系统的缺乏理解是非常令人遗憾的，因为这些化合物表现出最高的体超导转变温度，并且与其他类别存在显著差异，例如更高程度的轨道简并性和垂直于层的降低的电子色散。质量和组成。由于晶体生长的主要挑战，1111家族目前是所有IBS中了解最少的。直到最近，PI Wurmehl在德累斯顿IFW的小组中才使用固态单晶生长法生长出了具有相当大c轴生长的大而多面的LaFeAsO单晶。这种方法通常不为人所知，也不被完全理解，生长是扩散控制的，晶体是通过异常晶粒生长从多晶基质生长的。LaFeAsO晶体生长的成功将为化学和物理领域令人兴奋的实验奠定基础。我们希望利用1111晶体的首次可用性提供的机会，将晶体生长的努力与使用X射线和中子辐射的散射研究相结合。因此，我们要澄清的晶体结构，特别是要寻找的结构扭曲证明NQR实验。我们将描述磁序和短程磁关联作为组成，温度和单轴应变的函数。磁激发被认为是超导配对的关键元素，当大量的晶体可用时，可以通过非弹性中子散射来研究。研究具有更高转变温度的材料中的超导自旋共振模和研究具有不同电子结构的1111材料中的自旋空间各向异性似乎是最有趣的。