Origin of the Higher-Tc Phase in the KxFe2−ySe2 System

• DOI: 10.7566/jpsj.85.044710
• Publication Date: 2016-03-31T01:26:21Z
• Authors: Masashi Tanaka; Yusuke Yanagisawa; Saleem J. Denholme; Masaya Fujioka; Shiro Funahashi; Yoshitaka Matsushita; Nobuo Ishizawa; Takahide Yamaguchi; Hiroyuki Takeya; Yoshihiko Takano
• Keywords: Superconductivity (cond-mat.supr-con); 13. Climate action; Condensed Matter - Superconductivity; 0103 physical sciences; FOS: Physical sciences; 10. No inequality; 01 natural sciences

14 pages, 6 figures<br/>Single crystals of K$_x$Fe$_{2-y}$Se$_2$ are prepared by quenching at various temperatures. The crystals obtained at higher quenching temperatures have a surface morphology with mesh-like texture. They show a sharp superconducting transition at $T_\rm{c}$ ~32 K with a large shielding volume fraction. On the other hand, the crystals prepared without quenching show an onset superconducting transition at ~44 K and a zero resistivity around ~33 K, and they possess island-like regions on the surface with a larger amount of Fe incorporation. In-situ high-temperature single crystal X-ray diffraction measurements tell us the Fe-vacancy ordered phase is generated at a temperature region around 270 ��C via iron diffusion. The creation of this Fe-vacancy ordered phase may become a driving force of the growth of the higher $T_\rm{c}$ phase. The superconductivity at ~44 K is attributed to a metallic phase with no Fe-vacancy.<br/>