Phase separation and metallic conductivity in Tl_0.4K_0.4Fe_2−ySe_2−xS_x

¹ High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China Hefei 230026, PRC
² Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China Hefei 230026, PRC

^(a) zhangcj@hmfl.ac.cn (corresponding author)

Received: 21 September 2012
Accepted: 2 November 2012

Abstract

We study the effects of S-doping on the microstructure, magnetic and transport properties of the Tl_0.4K_0.4Fe_2−ySe_2−xS_x superconductor. At low doping level (x ⩽ 0.8), the samples exhibit behaviors similar to those of the parent sample, i.e., the occurrence of phase separation into a Fe-vacancy phase, a charge ordering phase and an undistorted phase; the presence of a “hump”-like feature in the resistivity curves; and the development of antiferromagnetic order well above room temperature. In sharp contrast, the samples with x ⩾ 1.0 all exhibit metallic-like behavior without displaying superconductivity. And these samples are chemically phase separated into a S-poor Tl_0.4K_0.4Fe_2−ySe_2−xS_x-phase and a S-rich Tl_0.4K_0.4Fe_2−yS₂-phase. Interestingly, the Fe-vacancy phase is absent in these samples, accompanied with the disappearance of semiconducting-like conductivity at high temperature and the depression of superconductivity. The charge ordering phase is responsible for the metallic behavior in heavily doped samples.