Crystal growth and annealing study of fragile, non-bulk superconductivity in YFe2Ge2

We investigated the occurrence and nature of superconductivity in single crystals of grown out of Sn flux by employing X-ray diffraction, electrical resistivity and specific heat measurements. We found that the residual resistivity ratio (RRR) of single crystals can be greatly improved, reaching as high as , by decanting the crystals from the molten Sn at and/or by annealing at temperatures between 550 and . We found that the samples with RRR 34 showed resistive signatures of superconductivity with the onset of the superconducting transition . RRR values vary between 35 and 65 with, on average, no systematic change in value, indicating that the systematic changes in RRR do not lead to comparable changes in . Specific heat measurements on samples that showed the clear resistive signatures of a superconducting transition did not show any signature of a superconducting phase transition, which suggests that the superconductivity observed in this compound is either some sort of filamentary, strain-stabilized superconductivity associated with small amounts of stressed (perhaps at twin boundaries or dislocations) or is a second crystallographic phase that is present at level below detection capability of conventional powder X-ray techniques.