The Neutron Studies on the Influence of the Iron-Vacancy Order to the Superconductivity in K2Fe4Se5

Jie-Yu Yang^1,2*, Chih-Hao Lee¹, Maw-Kuen Wu²

¹工程與系統科學系, 國立清華大學, 新竹市, Taiwan
²物理所, 中央研究院, 台北市, Taiwan

* Presenter:Jie-Yu Yang, email:jyyang@phys.sinica.edu.tw

The nuclear and magnetic structure of polycrystalline K2-xFe4+ySe5 was examined through neutron powder diffraction (NPD). The magnetic structure showed checkerboard anti-ferromagnetic (AFM) superlattice in the parent compound K2Fe4Se5 sample, and √5×√5×1 iron-vacancy order was clearly observed. The iron-vacancy order plays a crucial role in superconductivity (SC). In order to study the interplay between the AFM and SC, a series of sample was prepared to do the NPD and neutron scattering. The apparent differences of the phonon/magnon excitations were found for the annealed and the quenched K2Fe4Se5 samples, while the iron-vacancy turns to disorder state in the quenched sample. For the annealed K2Fe4Se5 sample, the broad peak at 60 K splitting into two peaks at 300 K, which separates Verwey-like transition temperature at 125 K. As for the quenched K2Fe4Se5 sample, the 27 meV shifts to 24 meV, indicating distinct behavior for the two samples. It was confirmed that the 27 meV possibly be the magnon excitation. The information could provide important clues to the superconductivity in iron-based superconductors.

Keywords: iron-based superconductors, iron-vacancy, magnon excitation