Origin of the Higher-$T_\rm{c}$ Phase in the K$_x$Fe$_{2-y}$Se$_2$ System

Masashi Tanaka; Yusuke Yanagisawa; Masaya Fujioka; Saleem J. Denholme; Shiro Funahashi; Yoshitaka Matsushita; Nobuo Ishizawa; Takahide Yamaguchi; Hiroyuki Takeya; Yoshihiko Takano

doi:10.7566/jpsj.85.044710

arXiv · 1504.04197

Origin of the Higher-$T_\rm{c}$ Phase in the K$_x$Fe$_{2-y}$Se$_2$ System

Masashi Tanaka·Yusuke Yanagisawa·Masaya Fujioka·Saleem J. Denholme·Shiro Funahashi·Yoshitaka Matsushita·Nobuo Ishizawa·Takahide Yamaguchi·Hiroyuki Takeya·Yoshihiko Takano

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Abstract

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 {\deg}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.

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Masashi Tanaka, Yusuke Yanagisawa, Masaya Fujioka, Saleem J. Denholme, Shiro Funahashi, Yoshitaka Matsushita, Nobuo Ishizawa, Takahide Yamaguchi, Hiroyuki Takeya, Yoshihiko Takano. 2015-04-16. Origin of the Higher-$T_\rm{c}$ Phase in the K$_x$Fe$_{2-y}$Se$_2$ System. https://doi.org/10.7566/jpsj.85.044710

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