Electronic, structural, and magnetic properties of single crystalline pnictides: Thermodynamic studies down to ultra-low temperatures

为了研究铁基超导体中超导的性质以及磁性、结构和电子性质之间的相互作用，我们将应用热力学和磁学研究，直到10MK。为了研究超导电性，我们将利用现有的量热计和即将实现的基于磁测温仪的新设计的量热计，测量在10MK-4K的极低温度下9T以下的磁场中的比热。在相同温度条件下，磁化率和热传输测量将补充比热研究。我们将讨论由我们的SPP合作伙伴交付的面内和面外掺杂材料，即单晶K1-xNaxFe2As2，LiFeAs，K(Fe，M)2As2和Na(Fe，M)，其中M=Rh，Ru，Co，NiCrMn.此外，还将通过2-300K的热膨胀实验来研究电子自由度、磁场自由度和结构自由度的相互作用。在这里，除了研究Na(Fe，M)As，LaFeAsO单晶和多晶掺杂系列RFeAsO1-XFX，特别是四方相和向列相的磁短程有序。

We will apply thermodynamic and magnetic studies down to 10 mK in order to investigate the nature of superconductivity and the interplay of magnetism, structure, and electronic properties in Fe-based superconductors. For investigating superconductivity, we will perform measurements of the specific heat at very low temperatures 10 mK – 4 K in magnetic fields up to 9T by means of an existing calorimeter and a newly designed magnetic thermometry-based calorimeter which will be realized. The specific heat studies will be complemented by magnetic susceptibility and heat transport measurements in the same temperature regime. Both in-plane and out-of-plane doped materials will be addressed which are delivered by our SPP partners, i.e. single-crystalline K1- xNaxFe2As2, LiFeAs, K(Fe,M)2As2 and Na(Fe,M)As with M = Rh, Ru, Co,Ni Cr, Mn. In addition, the interplay of electronic, magnetic, and structural degrees of freedom will be studied by thermal expansion experiments at 2 – 300K. Here, in addition to Na(Fe,M)As, LaFeAsO single crystals and polycrystalline doping series RFeAsO1-xFx will be studied, with a particular focus on the tetragonal phase and nematic magnetic short-range order.