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

Abstract

This review focuses on the growth of high-quality (Li 1−x Fe x )OHFeSe single crystals by a hydrothermal method using floating-zone-grown A x Fe 2−y Se 2 (A = K, Rb, and Cs) as precursors. The structure, superconductivity, and magnetic behavior of the obtained crystals are highly influenced by the growth conditions, such as time, temperature, and composition. A phase diagram with temperature against the c-lattice constant is summarized including the antiferromagnetic spin density wave, superconducting, and paramagnetic phases.

Long-range magnetic order in hydroxide-layer-doped (Li1−x−yFexMnyOD)FeSe

“…Within the (LiOH)FeSe system, many factors that affect the observable superconducting temperature: lattice parameters, transition metal concentration in the hydroxide and selenide layers, and structural homogeneity. 4,8,41 Unlike previous reports, 9,10 no magnetic transition is observed in the magnetic susceptibility even at higher applied fields. Interestingly, the only reports to show a transition in magnetic susceptibility below the superconducting transition are on powder samples via hydrothermal method 9,10,41,56 .…”

“…Specifically where this behavior has been justified by strong vortex flow as well as a wide temperature range for vortex liquid behavior due to anisotropy and two-dimensionality. 8,39,58,[60][61][62][63] The superconducting onset temperature measured by resistivity is much higher than in the same crystal measured in magnetic susceptibility. This phenomena was observed in previous works as well and can be at- tributed to the vortex dynamics in the system 8,59,60,63 .…”

“…8,39,58,[60][61][62][63] The superconducting onset temperature measured by resistivity is much higher than in the same crystal measured in magnetic susceptibility. This phenomena was observed in previous works as well and can be at- tributed to the vortex dynamics in the system 8,59,60,63 . The residual resistivity ratio ρ(300K)/ρ(T c ) for the sample presented is ∼ 25 which is higher than in previous reports 8,[60][61][62] .…”

“…Interestingly, the only reports to show a transition in magnetic susceptibility below the superconducting transition are on powder samples via hydrothermal method 9,10,41,56 . Single crystals samples from the ion-exchange hydrothermal method fail to show the secondary magnetic transition below the observed superconducting transition 8,41,[57][58][59][60] . We hypothesize that sample uniformity in doping and structure caused by the different reaction conditions is likely the cause of these property differences.…”

“…The well-studied intercalated compound (Li 1−x Fe x OH)FeSe (T c = 42-44 K) consists of a tetragonal layer of partially charged Li 1−x Fe x OH (x ≈ 0.1-0.2) between the FeSe layers. Such a structure is stabilized by the partial charge transfer due to Fe doping on the Li site as well as hydrogen bonding from the LiOH layer to the Se atoms in the FeSe layers 3,7,8 . The Fe substitution in the insulating hydroxide layer not only plays a crucial role in the enhancement of T c , but also can induce exotic physical phenomena such as coexistence of magnetic order and superconductivity [9][10][11] .…”