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Register a new userBulk superconductivity in FeTe$_{1-x}$Se$_{x}$ via physicochemical pumping of excess iron
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The iron-based superconductor FeTe$_{1-x}$Se$_{x}$ has attracted considerable attention as a candidate topological superconductor owing to a unique combination of topological surface states and bulk high-temperature superconductivity. The superconducting properties of as-grown single crystals, however, are highly variable and synthesis dependent due to excess interstitial iron impurities incorporated during growth. Here we report a novel physicochemical process for pumping this interstitial iron out of the FeTe$_{1-x}$Se$_{x}$ matrix and achieving bulk superconductivity. Our method should have significant value for the synthesis of high-quality single crystals of FeTe$_{1-x}$Se$_{x}$ with large superconducting volume fractions.
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We have fabricated thin films of FeTe$_{1-x}$Se$_x$ using a scotch-tape method. The superconductivities of the thin films are different from each other although these films were fabricated from the same bulk sample. The result clearly presents the inhomogeneous superconductivity in FeTe$_{1-x}$Se$_x$. The difference comes from inhomogeneity due to the excess Fe concentration. The resistivity of a thin film with low excess Fe shows good superconductivity with the sharp superconducting-transition width and more isotropic superconductivity.
Recent investigations have shown that Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ can be made superconducting by annealing it in Se and O vapors. The current lore is that these chalcogen vapors induce superconductivity by removing the magnetic excess Fe atoms. To investigate this phenomenon we performed a combination of magnetic susceptibility, specific heat and transport measurements together with scanning tunneling microscopy and spectroscopy and density functional theory calculations on Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ treated with Te vapor. We conclude that the main role of the Te vapor is to quench the magnetic moments of the excess Fe atoms by forming FeTe$_{m}$ (m $geq$ 1) complexes. We show that the remaining FeTe$_{m}$ complexes are still damaging to the superconductivity and therefore that their removal potentially could further improve superconductive properties in these compounds.
In as-grown bulk crystals of Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ with $xlesssim0.3$, excess Fe ($y>0$) is inevitable and correlates with a suppression of superconductivity. At the same time, there remains the question as to whether the character of the antiferromagnetic correlations associated with the enhanced anion height above the Fe planes in Te-rich samples is compatible with superconductivity. To test this, we have annealed as-grown crystals with $x=0.1$ and 0.2 in Te vapor, effectively reducing the excess Fe and inducing bulk superconductivity. Inelastic neutron scattering measurements reveal low-energy magnetic excitations consistent with short-range correlations of the double-stripe type; nevertheless, cooling into the superconducting state results in a spin gap and a spin resonance, with the extra signal in the resonance being short-range with a mixed single-stripe/double-stripe character, which is different than other iron-based superconductors. The mixed magnetic character of these superconducting samples does not appear to be trivially explainable by inhomogeneity.
We found that hot alcoholic beverages were effective in inducing superconductivity in FeTe$_{0.8}$S0$_{.2}$. Heating FeTe$_{0.8}$S0$_{.2}$ compound in various alcoholic beverages enhances the superconducting properties compared to pure water-ethanol mixture as a control. Heating with red wine for 24 hours leads to the largest shielding volume fraction of 62.4% and the highest zero resistivity temperature of 7.8 K. Some components present in alcoholic beverages, other than water and ethanol, have the ability to induce superconductivity in FeTe$_{0.8}$S0$_{.2}$ compound.
The magnetic properties attributed to the hydroxide layer of Li1-xFex(OH)Fe1-ySe have been elucidated by the study of superconducting and nonsuperconducting members of this family. Both ac magnetometry and muon spin relaxation measurements of nonsuperconductors find a magnetic state existing below approximately 10 K which exhibits slow relaxation of magnetization. This magnetic state is accompanied by a low-temperature heat capacity anomaly present in both superconducting and nonsuperconducting variants suggesting that the magnetism persists into the superconducting state. The estimated value of magnetic moment present within the hydroxide layer supports a picture of a glassy magnetic state, probably comprising clusters of iron ions of varying cluster sizes distributed within the lithium hydroxide layer.
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