Low-temperature heat capacity of superconducting ternary iron silicides

The low-temperature heat capacity of superconducting ternary iron silicides ${\mathrm{Lu}}_2$ ${\mathrm{Fe}}_3$ ${\mathrm{Si}}_5$, ${\mathrm{Sc}}_2$ ${\mathrm{Fe}}_3$ ${\mathrm{Si}}_5$, and ${\mathrm{Y}}_2$ ${\mathrm{Fe}}_3$ ${\mathrm{Si}}_5$ has been measured, revealing several anomalous properties of the superconducting state of these materials. These materials show a large linear term in the superconducting heat capacity and a reduced normalized jump in the specific heat at $T_c$. A two-band model is proposed to explain these properties and previously reported anomalous properties of superconducting ternary iron silicides.