Superconducting properties of YxLu1−xNi2B2C and La3Ni2B2N3−δ: A comparison between experiment and Eliashberg theory

Abstract

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-heat difference ΔC, the thermodynamic critical field Hc(T), as well as the upper critical field Hc2(T). These properties were analyzed within the Eliashberg theory including anisotropy effects, yielding electron-phonon coupling anisotropy parameters 〈ak2〉 ranging between 0.02 and 0.03 for the whole series, and Fermi velocity anisotropy parameters of 〈bk2〉=0.245–0.3. Excellent agreement between theory and experiment was achieved for these parameters, the Sommerfeld constant γ and model phonon spectra determined from specific heat measurements. An analysis of the previously investigated boronitride La3Ni2B2N3−δ for comparison revealed the electron-phonon anisotropy to be of great significance in describing its thermodynamic properties and the calculations yielded 〈ak2〉≃0.08 and 〈bk2〉≃0.245. The Tc behavior within the series YxLu1−xNi2B2C is discussed in terms of the density of states at the Fermi level N(0).

Source-reported materials — not catalogue approval

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