Disordered Fe vacancies and superconductivity in potassium-intercalated iron selenide (K_2−xFe_4+ySe₅)

¹ Institute of Physics, Academia Sinica - Taipei, Taiwan
² Department of Electronic and Computer Engineering, National Taiwan University of Science and Technology Taipei, Taiwan
³ Department of Physics, National Tsing Hua University - Hsinchu, Taiwan
⁴ Institute of Astrophysics and Astronomy, Academia Sinica - Taipei, Taiwan
⁵ Deparment of Applied Physics and Geballe Laboratory for Advanced Materials, Stanford University Stanford, CA, USA
⁶ National Donghwa University - Hualien, Taiwan

^(a) mkwu@phys.sinica.edu.tw (corresponding author)

Received: 1 June 2015
Accepted: 20 July 2015

Abstract

In the high-T_c potassium-intercalated FeSe, there has been significant debate regarding what the exact parent compound is. Here we show that the Fe-vacancy ordered K₂Fe₄Se₅ is the magnetic, Mott insulating parent compound of the superconducting state. Non-superconducting K₂Fe₄Se₅ becomes a superconductor after high-temperature annealing, and the overall picture indicates that superconductivity in K_2−xFe_4+ySe₅ originates from the Fe-vacancy order-to-disorder transition. Thus, the long-pending question as to whether magnetic and superconducting state are competing or cooperating for cuprate superconductors may also apply to the Fe-chalcogenide superconductors. It is believed that the iron selenides and related compounds will provide essential information to understand the origin of superconductivity in the iron-based superconductors, and possibly to the superconducting cuprates.