Coexistence of superconductivity and antiferromagnetism in single crystals A_0.8Fe_2−ySe₂ (A = K, Rb, Cs, Tl/K and Tl/Rb): Evidence from magnetization and resistivity

Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China - Hefei, Anhui 230026, PRC

^a chenxh@ustc.edu.cn

Received: 16 February 2011
Accepted: 21 March 2011

Abstract

We measure the resistivity and magnetic susceptibility in the temperature range from 5 K to 600 K for the single crystals AFe_2−ySe₂ (A = K_0.8, Rb_0.8, Cs_0.8, Tl_0.5K_0.3 and Tl_0.4Rb_0.4). A sharp superconducting transition is observed in low-temperature resistivity and susceptibility, and the fully shielding fraction shows bulk susceptibility for all the crystals, while an antiferromagnetic transition is observed in susceptibility at Néel temperature (T_N) as high as 500 K to 540 K depending on A. This indicates the coexistence of superconductivity and antiferromagnetism in these intercalated iron selenides. A sharp increase in resistivity arises from the structural transition due to Fe vacancy ordering at temperature slightly higher than T_N. Occurrence of superconductivity in an antiferromagnetic ordered state with so high T_N may suggest new physics in this type of unconventional superconductors.