Review of annealing effects and superconductivity in Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ superconductors

Abstract

Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ is unique in their structural simplicity, consisting of only FeTe/Se layers, which is favorable for probing the mechanism of superconductivity. Recently, a topological surface superconductivity as well as the Majorana Fermions has been observed, which makes Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ the first high temperature topological superconductor. Since large size single crystal of Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ can be easily grown, many researches have been performed. However, a large part of the reported results are under controversy, including the resistivity, susceptibility, Hall effect, gap structure, phase diagram, etc. These controversies are believed to come from the sample-dependent Fe nonstoichiometries, which originate from the partial occupation of the second Fe site (excess Fe) in the Te/Se layer. The excess Fe with valence near Fe${}^{+}$ will provide electron doping into the system. Meanwhile, the excess Fe is also strongly magnetic, which will act as a paring breaker and also localize the charge carriers. Removing the excess Fe is essential to probe the intrinsic properties and mechanism of superconductivity of Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ compounds. In this topical review, we propose the effective approaches to remove excess Fe in Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$. Furthermore, we discuss the mechanism of annealing based on the evolutions of structure, composition, and morphology with annealing. Moreover, we also review the annealing effects on the normal state and superconducting properties, including the magnetism, transport properties, band structure, $T_{\mathrm{c}}$, phase diagram, upper critical field, anisotropy, critical current density, gap structure, and superconducting pairing. This review presents not only the optimal way to prepare crystals without excess Fe, but also the intrinsic properties of Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ without the influence of excess Fe.

review paper; 38 pages, 33 figures

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Cited by in corpus (32)

• On the Remarkable Superconductivity of FeSe and its Close Cousins
• Magnetic, superconducting, and topological surface states on Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$
• Pure nematic quantum critical point accompanied by a superconducting dome
• Annealing-tunable charge density wave in the kagome antiferromagnet FeGe
• Visualizing nematic transition and nanoscale suppression of superconductivity in Fe(Te,Se)
• Hydrothermal synthesis and complete phase diagram of FeSe${}_{1-x}$S${}_x$ $(0\le x\le 1)$ single crystals
• Enhanced superconducting pairing strength near a nonmagnetic nematic quantum critical point
• Achieving the depairing limit along $c$ axis in Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ single crystals
• Electronic transport properties and hydrostatic pressure effect of FeSe${}_{0.67}$Te${}_{0.33}$ single crystals free of phase separation
• Significant enhancement of critical current density in H+-intercalated FeSe single crystal
• Comparative study of superconducting and normal-state anisotropy in Fe${}_{1+y}$Te${}_{0.6}$Se${}_{0.4}$ superconductors with controlled amounts of interstitial excess Fe
• Molecular beam epitaxy of superconducting FeSe${}_x$Te${}_{1-x}$ thin films interfaced with magnetic topological insulators
• Nematic Fluctuations in an Orbital Selective Superconductor Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$
• Bulk and surface Dirac states accompanied by two superconducting domes in FeSe-based superconductors
• Bulk superconductivity in FeTe${}_{1-x}$Se${}_x$ via physicochemical pumping of excess iron
• Stoichiometric FeTe is a Superconductor
• Thickness-induced crossover from strong to weak collective pinning in exfoliated FeTe${}_{0.6}$Se${}_{0.4}$ thin films at 1 T
• Structural analysis and transport properties of [010]-tilt grain boundaries in Fe(Se,Te)
• Critical Current Density and AC Magnetic Susceptibility of High-quality FeTe${}_{0.5}$Se${}_{0.5}$ Superconducting Tapes
• Mystery of superconductivity in FeTe films and the role of neighboring layers
• In-plane p-wave coherence length in iron-based superconductors
• In-situ electrical and thermal transport properties of FeySe1-xTex films with ionic liquid gating
• Electronic phase diagram of Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ revealed by magnetotransport measurements
• Band Engineering of Dirac cones in Iron Chalcogenides
• Unusual spin-triplet superconductivity in monolayer graphene
• Intrinsic coherence length anisotropy in nickelate, and some pnictide, and chalcogenide superconductors
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