ELECTRON-PHONON COUPLING ORIGIN OF THE RESISTIVITY IN YNi2B2C SINGLE CRYSTALS

Abstract

Resistivity measurements from 4.2 K up to 300 K were made on YNi 2 B 2 C single crystals with T c = 15.5 K . The resulting ρ(T) curve shows a perfect Bloch-Grüneisen (BG) behavior, with a very small residual resistivity which indicates the low impurity content and the high cristallographic quality of the samples. The value λ tr = 0.53 for the transport electron-phonon coupling constant was obtained by using the high-temperature constant value of d ρ/ d T and the plasma frequency reported in literature. The BG expression for the phononic part of the resistivity ρ ph (T) was then used to fit the data in the whole temperature range, by approximating [Formula: see text] with the experimental phonon spectral density G(Ω) multiplied by a two-step weighting function to be determined by the fit. The resulting fitting curve perfectly agrees with the experimental points. We also solved the real-axis Eliashberg equations in both s- and d-wave symmetries under the approximation [Formula: see text]. We found that the value of λ tr here determined in single-band approximation is quite compatible with T c and the gap Δ experimentally observed. Finally, we calculated the normalized tunneling conductance, whose comparison with break-junction tunnel data gives indication of the possible s-wave symmetry for the order parameter in YNi 2 B 2 C .