Search for New Superconductors: an Electro-Magnetic Phase Transition in an Iron Meteorite Inclusion at 117 K
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The discovery of superconductivity in pnictides and iron chalcogenides inspires the search for new iron-based superconducting phases. Iron-rich meteorites present a unique opportunity for this search because they contain a broad range of compounds produced under extreme growth conditions. We investigated a natural iron sulfide-based material (troilite) inclusion with its associated minerals in the iron meteorite (Fe, Ni), Tlacotepec. Tlacotepec cooled over the course of 10 6–10 7 years in an asteroidal core under high pressure while insoluble sulfur-rich materials segregated into inclusions within the Fe–Ni core, synthesizing minerals under conditions not possible in the laboratory. The search for superconductivity in these heterogeneous materials requires a technique capable of detecting minute amounts of a superconducting phase embedded in a non-superconducting matrix. We used magnetic field modulated microwave spectroscopy (MFMMS), the most sensitive, selective, and non-destructive technique, to search for superconductivity in heterogeneous systems. Here, we report the observation of an electro-magnetic phase transition (EMPT) at 117 K that produces a unique MFMMS response. A pronounced and reproducible peak proves the appearance of an EMPT at 117 K. The temperature of this transition is not influenced by moderate magnetic fields up to 1400 Oe. Further, hysteretic isothermal field sweep loops are typical of the field sweep loops caused by flux trapping in high T c superconductors. Although the compound responsible for the peak in the MFMMS spectra was not identified, our results indicate that it is a material heterogeneously distributed over the inclusion and possibly an iron sulfide-based phase.
KeywordsSuperconductivity Extraterrestrial materials Microwave absorption Iron sulfide
This research was supported by an Air Force Office of Scientific Research (AFOSR) grant FA9550-14-1-0202. We thank Neil Dilley from Quantum Design for helping us with the SQUID and AC susceptibility measurements. S.G. thanks József Fortágh for giving him the opportunity to finish this work. We thank Harold Weinstock for his original idea on the search for superconductivity in unconventional materials. J.G.R. kindly acknowledges support from Fondo de Apoyo para Profesores Asistentes (FAPA) program through Facultad de Ciencias and Vicerrectoria de Investigaciones of Universidad de los Andes, Bogotá Colombia.
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