Composition dependence of bulk superconductivity in YFe2Ge2

In the layered iron-based superconductor YFe2Ge2, a high Sommerfeld ratio of ∼100 mJ/(mol K^2) and a T^(3/2) temperature dependence of the electrical resistivity at low temperature T indicate strong electronic correlations and point towards an unconventional pairing state. We have investigated the role of composition and annealing conditions in optimizing the growth of high-quality YFe2Ge2. Our findings confirm that bulk superconductivity is observed in samples with disorder scattering rates less than 2k_BTc/(h/2pi). Fe deficiency on the Fe site is identified as the dominant source of disorder, which can be minimised by precipitating from a slightly iron-rich melt, following by annealing.