Superconducting properties of YxLu1-xNi2B2C and La3Ni2B2N3-δ:: A comparison between experiment and Eliashberg theory -: art. no. 104508

Specific heat and resistivity measurements were performed on polycrystalline samples of the solid-solution YxLu1-xNi2B2C in order to determine thermodynamic properties such as the specific-heal difference DeltaC, the thermodynamic critical field H-c(T), as well as the upper critical field H-c2(T). These properties were analyzed within the Eliashberg theory including anisotropy effects, yielding electron-phonon coupling anisotropy parameters (a(k)(2)) ranging between 0.02 and 0.03 for the whole series, and Fermi velocity anisotropy parameters of (b(k)(2))=0.245-0.3. Excellent agreement between theory and experiment was achieved for these parameters, the Sommerfeld constant gamma and model phonon spectra determined from specific heat measurements. An analysis of the previously investigated boronitride La3Ni2B2N3-delta for comparison revealed the electron-phonon anisotropy to be of great significance in describing its thermodynamic properties and the calculations yielded (a(k)(2)) similar or equal to 0.08 and (b(k)(2)) similar or equal to 0.245. The T-c behavior within the series YxLu1-xNi2B2C is discussed in terms of the density of states at the Fermi level N(0).