Unconventional Superconductivity in the Layered Iron Germanide YFe sub(2) Ge sub(2)

The iron-based intermetallic YFe sub(2) Ge sub(2) stands out among transition metal compounds for its high Sommerfeld coefficient of the order of 100mJ/(molK super(2)), which signals strong electronic correlations. A new generation of high quality samples of YFe sub(2) Ge sub(2) show superconducting transition anomalies below 1.8 K in thermodynamic, magnetic, and transport measurements, establishing that superconductivity is intrinsic in this layered iron compound outside the known superconducting iron pnictide or chalcogenide families. The Fermi surface geometry of YFe sub(2) Ge sub(2) resembles that of KFe sub(2) As sub(2) in the high pressure collapsed tetragonal phase, in which superconductivity at temperatures as high as 10 K has recently been reported, suggesting an underlying connection between the two systems.