Search for New Superconductors: An Electro-Magnetic Phase Transition in an Iron Meteorite Inclusion at 117 K

Abstract

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 materials (Troilite) inclusion with its associated minerals in the iron meteorite Tlacotepec. Tlacotepec formed in an asteroidal core under high pressure and at high temperature over millions of years, while insoluble sulfur rich materials segregated into inclusions during cooling along with included minerals. 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), a very sensitive, selective, and non-destructive technique, to search for superconductivity in heterogeneous systems. Here, we report the observation of an electro-magnetic phase transition at 117 K that causes a MFMMS-response typical of a superconductor. A pronounced and reproducible peak together with isothermal magnetic field sweeps prove the appearance of a new electromagnetic phase below 117 K. This is very similar to the characteristic response due to flux trapping in a granular superconductor with a short coherence length. Although the compound responsible for the peak in the MFMMS-spectra was not identified, it is possibly an iron sulfide based phase, or another material heterogeneously distributed over the inclusion.