Low temperature heat capacity in the iron-based superconductor YFe${}_2$Ge${}_2$

Unconventional superconductivity is rare in transition metal compounds outside the layered iron pnictide/chalcogenide and cuprate material families. These systems typically have highly anisotropic electronic properties and nearly 2D Fermi surface geometries. The iron based unconventional superconductor YFe${}_2$Ge${}_2$, by contrast, displays a comparatively isotropic, 3D electronic structure. Its Sommerfeld ratio C/T, is enhanced by an order of magnitude above the band structure value to $\gamma$ $\sim$ 100 mJ/(mol K${}^2$) at low temperature, and it displays an anomalous form for the temperature dependence of the resistivity, $\rho$(T) = $\rho$0 + AT${}^{3/2}$. Theoretical proposals for the pairing mechanism in YFe${}_2$Ge${}_2$ include both triplet and singlet, s* order parameter wave functions, prompting a renewed effort to examine the heat capacity well below the transition temperature in newly available bulk superconducting single crystals.