Superconductivity in alkali metal intercalated iron selenides

Abstract

Alkali metal intercalated iron selenide superconductors A x Fe2-y Se2 (where A = K, Rb, Cs, Tl/K, and Tl/Rb) are characterized by several unique properties, which were not revealed in other superconducting materials. The compounds crystallize in overall simple layered structure with FeSe layers intercalated with alkali metal. The structure turned out to be pretty complex as the existing Fe-vacancies order below ~550 K, which further leads to an antiferromagnetic ordering with Néel temperature fairly above room temperature. At even lower temperatures a phase separation is observed. While one of these phases stays magnetic down to the lowest temperatures the second is becoming superconducting below ~30 K. All these effects give rise to complex relationships between the structure, magnetism and superconductivity. In particular the iron vacancy ordering, linked with a long-range magnetic order and a mesoscopic phase separation, is assumed to be an intrinsic property of the system. Since the discovery of superconductivity in those compounds in 2010 they were investigated very extensively. Results of the studies conducted using a variety of experimental techniques and performed during the last five years were published in hundreds of reports. The present paper reviews scientific work concerning methods of synthesis and crystal growth, structural and superconducting properties as well as pressure investigations.

Magnetic imaging of antiferromagnetic and superconducting phases in RbxFe2−ySeHazi1, Mousavi2, Dudin3 et al. 2018Phys. Rev. B41110View full textAdd to dashboardCite

“…Since the L 2,3 absorption spectrum results from the excitation of electrons from the core Fe 2p levels to unoccupied 3d states, these spectra are sensitive to the local bonding environment of Fe. The core-hole spin-orbit interaction leads to splitting of the final state into two manifolds corresponding to j = 3 2 and 1 2 , which are well separated in energy, resulting in the L 3 and L 2 structures at 707 and 720 eV, respectively. The branching ratio…”

“…The coexistence of superconductivity and antiferromagnetism has been observed in many iron-based compounds, and the intriguing balance between competing magnetic interactions is thought to be the key to understanding the origins of unconventional superconductivity. Alkali-metal-doped iron selenides (A x Fe 2−y Se 2 , A = K, Cs, Rb) are an extreme example, exhibiting superconducting properties up to the relatively high temperature of about 30 K and, simultaneously, antiferromagnetic ordering that persists up to temperatures as high as 500 K [1,2]. Microstructural studies have revealed that superconducting single crystals of these compounds are intrinsically phase separated, with a striking microstructure consisting of a three-dimensional array of the minority phase in the form of plates aligned along the crystallographic {103} planes [3,4].…”

Electronic Structure of FeSe Monolayer Superconductors: Shallow Bands and Correlations

“…It is generally believed that superconductivity in this system appears in an ideal 122-type structure, though most of the samples studied so far were multiphase, consisting of a mixture of mesoscopic superconducting and insulating (antiferromagnetic) structures (e.g. such as K 2 Fe 4 Se 5 ), complicating the studies of this system [12].…”

On the origin of the shallow and “replica” bands in FeSe monolayer superconductors, "Письма в Журнал экспериментальной и теоретической физики"

“…Further success in creation of intercalated FeSe based systems with rather high T c ∼ 30-40K (see review in [8,9]) quickly made them popular objects of investigations because of their different electronic structure [10,11].…”