Thermodynamic and Transport Properties of Iron-Pnictide Superconductors under hydrostatic (Hegas) pressure

静水压（Hegas）下铁磷族超导体的热力学和输运特性

• 批准号: 237626901
• 负责人: Professor Dr. Michael Lang
• 金额: --
• 依托单位: Physikalisches Institut
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2015-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/237626901?language=en
• 关键词: Thermodynamic; Transport; Properties; Iron; Pnictide

Among the various iron-arsenide-based superconductors, members of the AFe2As2 (A = Ba, Sr, Ca), the so-called 122 family, have become model systems for exploring superconductivity in this new class of high-Tc superconductors. This is partly related to the fact that for these systems large, high-quality, and homogeneous crystals can be grown. The (temperature vs chemical doping) phase diagrams of these materials have been explored extensively for unravelling the interplay of superconductivity with the nearby magnetic and structural orders – an aspect which has become a major theme of research in this class of materials.In this project we propose to study the interplay of superconductivity with the nearby magnetic and structural orders on selected members of the 122 family, especially Ca(Fe1- xCox)2As2, Ba(Fe1-xCox)2As2, Ca1-xSrxFe2As2, and Ba1-xKxFe2As2, via thermodynamic measurements under hydrostatic (He-gas) pressure. The work is motivated by our recent discovery, that for properly heat-treated crystals of Ca(Fe1-xCox)2As2 with x = 0.028, the salient ground states associated with iron-arsenide superconductors, i.e., orthorhombic/antiferromagnetic, superconducting, and non-magnetic collapsed tetragonal states can be accessed all in one sample with reasonably small and truly hydrostatic pressure.Through the combination of various thermodynamic (magnetic susceptibility, highresolution thermal expansion, ultrasonic) and transport (resistivity) measurements, all under truly hydrostatic (He-gas) pressure, we will address among others the following aspects: (i) The conditions under which superconductivity does or does not coexist with structural/magnetic order in the 122 family. (ii) Comparative investigations on the structural/magnetic fluctuations on systems showing first- and second-order phase transitions into the low-temperature orthorhombic/antiferromagnetic (o/afm) phase. (iii) The possibility of a tricritical point in the T-P phase diagram where the o/afm and superconducting phase transition lines meet. (iv) Detailed investigations on the interrelation of superconductivity and the occurrence of the collapsed-tetragonal phase on the high-pressure side. (v) Study of the elastic behavior upon pressure tuning across the phase diagram; comparison with the anomalous behaviour reported in the literature for materials with varying doping levels.

在各种砷化铁基超导体中，AFe2As2（A = Ba、Sr、Ca）（即所谓的 122 家族）的成员已成为探索此类新型高温超导体中超导性的模型系统。这部分与以下事实有关：对于这些系统，可以生长大的、高质量的且均匀的晶体。这些材料的（温度与化学掺杂）相图已被广泛探索，以揭示超导性与附近磁序和结构序的相互作用——这一方面已成为此类材料研究的一个主要主题。在这个项目中，我们建议研究 122 族的选定成员，特别是 Ca(Fe1-xCox)2As2 的超导性与附近磁序和结构序的相互作用， Ba(Fe1-xCox)2As2、Ca1-xSrxFe2As2 和 Ba1-xKxFe2As2，通过静水压（氦气）压力下的热力学测量。这项工作的动机是我们最近的发现，即对于 x = 0.028 的经过适当热处理的 Ca(Fe1-xCox)2As2 晶体，与铁砷化物超导体相关的显着基态，即正交/反铁磁、超导和非磁性塌陷四方态，可以在一个样品中以相当小的且真正的流体静力获得。 通过结合各种热力学（磁化率、高分辨率热膨胀、超声波）和输运（电阻率）测量，所有这些测量都在真正的静水压力（氦气）下进行，我们将解决以下几个方面的问题：（i）超导性与 122 系列中的结构/磁序共存或不共存的条件。 （ii）对显示一级和二级相变到低温正交/反铁磁（o/afm）相的系统的结构/磁波动的比较研究。 (iii) T-P 相图中 o/afm 和超导相变线相交处可能出现三临界点。 (iv) 详细研究超导性与高压侧塌陷四方相的相互关系。 (v) 研究相图中压力调节时的弹性行为；与文献中报道的不同掺杂水平材料的异常行为进行比较。