Novel Materials {\&} Multi-scale Analysis of the Superconducting State in Iron Based Superconductors

The understanding of the fundamental nature of a material's superconducting state is of crucial importance, if superconductors are to fulfill their promise for widespread use in energy-related needs. Our research applies multi-scale characterization techniques to study and probe the nuclear, electronic, and magnetic details of single crystals. The importance of such broad investigative work is demonstrated in our recent publication on praseodymium-doped BaFe$_{2}$As$_{2}$ for which non-uniform local distortions through isolated Pr atoms do not provide percolation path superconductivity [1]. For CaFe$_{2}$As$_{2}$, it is found that large Fermi-surface reconstruction in the non-magnetic phase causes a non-superconducting ground state [2], while different crystalline domains with varying lattice parameters are identified [3]. For Cu-doped BaFe$_{2}$As$_{2}$ it is found that orthorhombic distortion below T$_{\mathrm{s}}$ leads to magnetically ordered state of FeAs planes, hence no superconductivity [4]. Studies of this nature can yield groundbreaking results by demonstrating that many parameters can compete in a bulk material and even be spatially and electronically non-homogenous on nanometers. \\[4pt] [1] Phys. Rev. Lett. 112 (2014), 047005;\\[0pt] [2] Phys. Rev. Lett. 112 (2014), 186401;\\[0pt] [3] Sci. Reports 4 (2014), 4120;\\[0pt] [4] Phys. Rev. Lett. 113 (2014), 117001.