SUPERCONDUCTING PAIRING MECHANISM OF RARE-EARTH-NICKEL-BOROCARBIDES: EFFECTS OF ELECTRON–ELECTRON AND ELECTRON–PHONON INTERACTIONS

Abstract

Upon considering the three interactions namely, the electron–acoustic phonon, the electron–optical phonon and the Coulomb, the analytical solutions for the energy gap equation allows one to determine the electronic structure parameters to discuss the behavior of superconducting transition temperature (Tc) and isotope effect coefficient (α) for layered structure YNi2 B2C. Tc of 17 K is estimated for YNi2B2C with electron–acoustic phonon (λac) = 0.31, electron–optical phonon (λop) = 0.1 and Coulomb screening parameter (μ*) = 0.126 indicating that the YNi2B2C superconductor is in the intermediate coupling regime. To correlate the Tc with various coupling strengths as λac, λop and μ*, we present curves of Tc with them. The present approach also explains the conditions for the Boron and Carbon isotope effect. The negative pressure coefficient of Tc in this layered material is attributed to the contraction along c-axis under hydrostatic pressure. We suggest from these results that both the acoustic and optical phonons within the framework of a three-square well scheme consistently explains the effective electron–electron interaction leading to superconductivity in layered structure YNi2B2C.