Ab initio pseudopotential calculations for the electronic structure of low-Tc LuNi2B2C and the related compound LuNiBC.

Abstract

Ab initio pseudopotential calculations are performed for the electronic structure of the low-${\mathit{T}}_{\mathit{c}}$ intermetallics ${\mathrm{LuNi}}_{2}$${\mathrm{B}}_{2}$C and the related nonsuperconducting compound LuNiBC. Electronic structures of the two compounds are compared in great detail, especially in terms of the Fermi surfaces and the symmetry-decomposed density of states (DOS) near the Fermi level. The estimated electron-phonon coupling constant \ensuremath{\lambda} (0.8--1.1) from the heat-capacity data as well as from the calculated DOS at ${\mathit{E}}_{\mathit{F}}$ indicates that ${\mathit{T}}_{\mathit{c}}$ of ${\mathrm{LuNi}}_{2}$${\mathrm{B}}_{2}$C is reasonably well explained by the conventional Bardeen-Cooper-Schrieffer mechanism with intermediate coupling strength. The relatively high ${\mathit{T}}_{\mathit{c}}$ arises from the large DOS at the Fermi level. Absence of superconductivity in LuNiBC may be understood to be due to the reduced DOS at ${\mathit{E}}_{\mathit{F}}$. Unlike the high-${\mathit{T}}_{\mathit{c}}$ cuprates, the low-${\mathit{T}}_{\mathit{c}}$ ${\mathrm{LuNi}}_{2}$${\mathrm{B}}_{2}$C does not have the half-filled \ensuremath{\sigma}-antibonding bands and its electronic structure is almost three dimensional despite the layered atomic structure.