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Register a new userSuperconductivity in Mg10Ir19B16
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Mg10Ir19B16, a previously unreported compound in the Mg-Ir-B chemical system, is found to be superconducting at temperatures near 5 K. The fact that the compound exhibits a range of superconducting temperatures between 4 and 5 K suggests that a range of stoichiometries is allowed, though no structural evidence for this is observed. The compound has a large, noncentrosymmetric, body centered cubic unit cell with a = 10.568 Angstrom, displaying a structure type for which no previous superconductors have been reported.
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The authors report on electron transport studies on superconductor-semiconductor hybrid structures of indium and n-type lead telluride, either in the form of quantum wells or bulk crystals. In-PbTe contacts form by spontaneous alloying, which occurs already at room temperature. The alloyed phase penetrates deeply into PbTe and forms metallic contacts even in the presence of depletion layers at the semiconductor surface. Although the detailed structure of this phase is unknown, we observe that it exhibits a superconducting transition at temperatures below 10 K. This causes such substantial reduction of the contact resistances that they even become comparable to those predicted for ideal superconductor-normal conductor contacts. Most importantly, this result indicates that the interface phase in the superconducting state becomes nearly homogeneous - in contrast to the structure expected for alloyed contacts. We suggest that the unusual interface superconductivity is linked to the unique properties of PbTe, namely, its huge static dielectric constant. Apparently the alloyed interface phase contains superconducting precipitates randomly distributed within the depletion layers, and their Coulomb charging energies are extremely small. According to the existing models of the granular superconductivity, even very weak Josephson coupling between the neighboring precipitates gives rise to the formation of a global superconducting phase which explains our observations.
Subsequent to our recent report of SDW type transition at 190 K and antiferromagnetic order below 20 K in EuFe2As2, we have studied the effect of K-doping on the SDW transition at high temperature and AF order at low temperature. 50% K doping suppresses the SDW transition and in turn gives rise to high-temperature superconductivity below T_c = 32 K, as observed in the electrical resistivity, AC susceptibility as well as magnetization. A well defined anomaly in the specific heat provides additional evidence for bulk superconductivity.
High-pressure electrical resistance measurements have been performed on single crystal Ba0.5Sr0.5Fe2As2 platelets to pressures of 16 GPa and temperatures down to 10 K using designer diamond anvils under quasi-hydrostatic conditions with an insulating steatite pressure medium. The resistance measurements show evidence of pressure-induced superconductivity with an onset transition temperature at ~31 K and zero resistance at ~22 K for a pressure of 3.3 GPa. The transition temperature decreases gradually with increasing in pressure before completely disappearing for pressures above 12 GPa. The present results provide experimental evidence that a solid solution of two 122-type materials, e.g., Ba1-x.SrxFe2As2 (0 < x <1), can also exhibit superconductivity under high pressure
Organometallic compounds constitute a very large group of substances that contain at least one metal-to-carbon bond in which the carbon is part of an organic group. They have played a major role in the development of the science of chemistry. These compounds are used to a large extent as catalysts (substances that increase the rate of reactions without themselves being consumed) and as intermediates in the laboratory and in industry. Recently, novel quantum phenormena such as topological insulators and superconductors were also suggested in these materials. However, there has been no report on the experimental exploration for the topological state. Evidence for superconductivity from the zero-resistivity state in any organometallic compound has not been achieved yet, though much efforts have been devoted. Here we report the experimental realization of superconductivity with the critical temperature of 3.6 K in a potassium-doped organometallic compound, $ i.e.$ tri-$o$-tolylbismuthine with the evidence of both the Meissner effect and the zero-resistivity state through the $dc$ and $ac$ magnetic susceptibility and resistivity measurements. The obtained superconducting parameters classify this compound as a type-II superconductor. The benzene ring is identified to be the essential superconducting unit in such a phenyl organometallic compound. The superconducting phase and its composition are determined by the combined studies of the X-ray diffraction and theoretical calculations as well as the Raman spectroscopy measurements. These findings enrich the applications of organometallic compounds in superconductivity and add a new electron-acceptor family for organic superconductors. This work also points to a large pool for finding superconductors from organometallic compounds.
Single crystals of the compound LaFePO were prepared using a flux growth technique at high temperatures. Electrical resistivity measurements reveal metallic behavior and a resistive transition to the superconducting state at a critical temperature T_c ~ 6.6 K. Magnetization measurements also show the onset of superconductivity near 6 K. In contrast, specific heat measurements manifest no discontinuity at T_c. These results lend support to the conclusion that the superconductivity is associated with oxygen vacancies that alter the carrier concentration in a small fraction of the sample, although superconductivity characterized by an unusually small gap value can not be ruled-out. Under applied magnetic fields, T_c is suppressed anisotropically for fields perpendicular and parallel to the ab-plane, suggesting that the crystalline anisotropy strongly influences the superconducting state. Preliminary high-pressure measurements show that T_c passes through a maximum of nearly 14 K at ~ 110 kbar, demonstrating that significantly higher T_c values may be achieved in the phosphorus-based oxypnictides.
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