ELECTRON-DENSITY OF STATES IN THE BOROCARBIDE INTERMETALLIC SUPERCONDUCTORS

We present heat-capacity measurements in a magnetic field up to 7.7 T on the recently discovered borocarbide intermetallic superconductors LuNi2B2C and LaPt1.7Au0.3B2C. For LuNi2B2C with T(c) = 16.5 K, we find a large density of states at the Fermi level, gamma approximately 19(2) mJ/mole K2, and an effective Debye temperature THETA(D) of 345 K. In comparison, LaPt1.7Au0.3B2C, with T(c) = 10.2 K, has a gamma of 7.5(1.5) mJ/mole K2 and a smaller Debye temperature THETA(D) of 220 K. Through comparison with the specific-heat anomaly at T(c), DELTAC/gammaT(c), the magnetic susceptibility, and the calculated band structure, these compounds are found to be in the weak-to-intermediate coupling limit with lambda = 0.5-1.0. Their position on the gamma-T(c) plot indicates dominant phonon-mediated electron pairing.