Fe-vacancy order and superconductivity in tetragonal β -Fe _{1- x} Se

Abstract

Several superconducting transition temperatures in the range of 30–46 K were reported in the recently discovered intercalated FeSe system (A1-xFe2-ySe2, A = K, Rb, Cs, Tl). Although the superconducting phases were not yet conclusively decided, more than one magnetic phase with particular orders of iron vacancy and/or potassium vacancy were identified, and some were argued to be the parent phase. Here we show the discovery of the presence and ordering of iron vacancy in nonintercalated FeSe (PbO-type tetragonal β-Fe1-xSe). Three types of iron-vacancy order were found through analytical electron microscopy, and one was identified to be nonsuperconducting and magnetic at low temperature. This discovery suggests that the rich-phases found in A1-xFe2-ySe2 are not exclusive in Fe-Se and related superconductors. In addition, the magnetic β-Fe1-xSe phases with particular iron-vacancy orders are more likely to be the parent phase of the FeSe superconducting system instead of the previously assigned β-Fe1+δTe.

Giant increase of critical current density and vortex pinning in Mn doped KxFe2−ySe2 single crystals

“…19 On the other hand, the variations of K atoms 6,36 probably serve as the major normal point pinning centers in K z Fe 2 Se 2 even though the lattice defects, e.g., Fe/Se vacancies cannot be totally excluded. 15,16,37,38 As shown in the insets of Fig. 2(b) and Fig.…”

Tunable critical temperature for superconductivity in FeSe thin films by pulsed laser deposition

“…Therefore, considering the composition off-stoichiometry for the superconductivity of FeSe films, namely the vacancies or interstitial impurity 30,32 , we prepared the targets with subtle adjustment in the nominal Fe:Se, including 1:1.10, 1:1.05, 1:1.03, 1:1.00, 1:0.99, 1:0.97, 1:0.95, 1:0.90, and so on. For comparison, the films were grown with the same thickness of ~160 nm and on the same CF substrate.…”

(Li1−xFex)OHFeSe Superconductors: Crystal Growth, Structure, and Electromagnetic Properties

“…Since their discovery, iron-selenide SCs have been found to provide a strong platform for the investigation of their high-T c superconductivity, since they possess a simple structure, are nontoxic, and may be fabricated via numerous synthesis methods [2,18,33,34]. The simplest tetragonal β-Fe 1+δ Se (11-system) has T c ≈ 8.5 K at ambient pressure and is sensitive to chemical and physical pressure effects [35]. It was observed that T c can be increased up to 15 K in the β-Fe 1+δ Se system by partially replacing Se with Te and up to 36.7 K under the application of a hydrostatic pressure of 8.9 GPa [36,37].…”