Unconventional Bulk Superconductivity in YFe2Ge2 Single Crystals

Sharp superconducting transition anomalies observed in a new generation of single crystals establish that bulk superconductivity is intrinsic to high purity YFe2Ge2. Low temperature heat capacity measurements suggest a disorder and field dependent residual Sommerfeld coefficient, consistent with disorder-induced in-gap states as expected for a sign-changing order parameter. The sevenfold reduction in disorder scattering in these new crystals to residual resistivities similar or equal to 0.45 mu Omega cm was achieved using a new liquid transport growth technique, paving the way for multiprobe experiments investigating the normal and superconducting states of YFe2Ge2.