Superconducting properties of Y_xLu_(1-x)Ni2B2C and La3Ni2B2N3: A comparison between experiment and Eliashberg theory

TL;DR

This study investigates the superconducting properties of Y_xLu_(1-x)Ni2B2C and La3Ni2B2N3, comparing experimental measurements with Eliashberg theory predictions, revealing detailed insights into electron-phonon coupling and anisotropy effects.

Contribution

The paper provides a comprehensive comparison of experimental data with Eliashberg theory for these compounds, highlighting the importance of anisotropy in their superconducting behavior.

Findings

Excellent agreement between theory and experiment for anisotropy parameters.

Electron-phonon anisotropy significantly influences thermodynamic properties.

The T_c-behavior is affected by coupling, impurity effects, and density of states.

Abstract

Specific heat and resistivity measurements were performed on polycrystalline samples of the solid-solution Y_xLu_(1-x)Ni2B2C in order to determine thermodynamic properties such as the specific-heat difference, 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 beween 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 and model phonon spectra determined from specific heat measurements. An analysis of the previously investigated boronitride La3Ni2B2N3 for comparison revealed the electron-phonon anisotropy to be of great significance in describing its thermodynamic properties and the calculations yielded <a_k^2> \~ 0.08 and <b_k^2> ~ 0.245. The T_c-behavior within the series Y_xLu_(1-x)Ni2B2C is discussed in terms of coupling and impurity effects, and the density of states at the Fermi level N(0).