The blue points are the coincident antiferromagnetic and orthorhombic transition temperatures, TN, into the C2 phase, and the red points are the observed transition temperatures, Tr, into the C4 phase. The green points are the superconducting transition temperatures, Tc, determined from magnetization data.
Magnetically Driven Suppression of Nematic Order in an Iron-based Superconductor
Magnetic order affects the atomic structure. At room temperature, the iron atoms sit on a square lattice, which has four-fold symmetry, but when cooled below the magnetic transition temperature, they distort to form a rectangular lattice, with only two-fold symmetry. This is sometimes called “nematic order.” It was thought that this nematic order persists until the material becomes superconducting - until our observation in neutron powder diffraction study on Ba1-xNaxFe2As2. We discovered a phase where the material returns to four-fold C4 symmetry, rather than two-fold C2, close to the onset of super-conductivity. The experimental results provide strong evidence for the validity of an itinerant model of nematic order in the iron-based superconductors, in which the orbital reconstruction of the iron 3d states is a consequence of magnetic interactions induced by Fermi surface nesting. Whether nematic order, or at least strong nematic fluctuations, is a prerequisite for superconductivity is another challenge to address in the future. This research was performed by a collaborative work of EM group and NXS group at MSD.
Related Article
“Magnetically-Driven Suppression of Nematic Order in the Iron-Based Superconductors”
S. Avci, O. Chmaissem, J.d Allred, S. Rosenkranz, I. Eremin, A. Chubukov, D. Bugaris, D.Y. Chung, M. Kanatzidis, J.-P. Castellan , J. Schlueter, H. Claus, D. Khalyavin, P. Manuel, A. Daoud-Aladine
Nature Comm., 2014, 5, 3845.