Phase Diagram of Ba1-xKxFe2As2
Structural, magnetic, and superconducting phase diagram of Ba1-xK1-xFe2As2.
Published May 7, 2012
The role of internal structural parameters that influence the band structure and the degree of moment localization in optimizing superconductivity and the implications for the gap symmetry in Ba1−xKxFe2As2 remains a matter of debate.
Controlling the inhomogeneity to within acceptable limits to improve the accuracy of structural, magnetic, and superconducting phase boundaries has been a key goal of this work. We estimate that we have been able to synthesize samples for which Δx <0.01, suitable for systematic investigation using high-resolution neutron and x-ray diffraction combined with magnetization measurements.
The resulting phase diagram shown at right reveals that at low doping, Ba1−xKxFe2As2 undergoes a coincident first-order structural and magnetic phase transition to an orthorhombic (O) structure and a striped antiferromagnet. The onset of superconductivity occurs at a critical concentration of x = 0.130(3), and the superconducting transition temperature Tc increases linearly with x until it crosses the AF/O phase boundary. Below this concentration, there is microscopic phase coexistence of the AF/O and superconducting order parameters, although a slight suppression of the AF/O order is evidence that the phases are competing. At higher doping, superconductivity has a maximum Tc of 38 K at x = 0.4 that falls to 3 K at x = 1.0.
Phase Diagram of Ba1−xKxFe2As2
S. Avci, O. Chmaissem, D. Y. Chung, S. Rosenkranz, E. A. Goremychkin, J. P. Castellan, I. S. Todorov, J. A. Schlueter, H. Claus, A. Daoud-Aladine, D. D. Khalyavin, M. G. Kanatzidis, and R. Osborn
Phys. Rev. B 85, 184507 (2012)