Heat Capacity of MgB_2: Evidence for Moderately Strong Coupling Behavior

Abstract

We characterize the superconducting state of phase pure polycrystalline samples of the new layered superconductor MgB${}_2$ by specific heat measurements in magnetic fields up to 9 T. The characteristic jump at the superconducting transition is observed and compared with the predictions of weak coupling BCS-theory and the $\alpha$-model. Our analysis shows excellent agreement with the predictions for 2$\Delta /k_B{T}_{\mathrm{C}}$ = 4.2(2) with a Sommerfeld term ${\gamma }_{\exp }$ of 3.1(1) mJ/mol K${}^2$ indicating that MgB${}_2$ is a superconductor in the moderately strong electron-phonon coupling regime.

10 pages, 3 figures. RevTeX. Submitted to Phys. Rev. Lett