The Specific Heat of Mg(B$_{1-x}$C$_{x}$)$_{2}$: Two-Gap Superconductors

Two polycrystalline samples of Mg(B$_{1-x}$C$_{x})_{2}$ were measured in magnetic fields (B) to 9 T. The samples show no evidence of magnetic impurities and have only small non-superconducting fractions. For x = 0.1, T$_{c}$ = 32 K and for x = 0.2, T$_{c}$ = 20 K. The specific heats of both samples can be fit with two superconducting energy gaps as was the case for MgB$_{2}$, although the magnitudes and fractions for each are different. For the two carbon-substituted samples the evolution of $\gamma $(B) with B, the normal state $\gamma $ values, and the Debye thetas will be compared to those of MgB$_{2}$.