Direct observation of a Fermi surface and superconducting gap in LuNi₂B₂C

We measured the Fermi surface (FS), band dispersion, and superconducting gap in LuNi₂B₂C using angle resolved photoemission spectroscopy. Experimental data were compared to the tight-binding version of the linear muffin-tin orbital (LMTO) method and linearized augmented plane-wave (LAPW) calculations. We found reasonable agreement between the two calculations and experimental data. The measured FS exhibits large parallel regions with a nesting vector that agrees with a previous positron annihilation study and calculations of the generalized susceptibility. The measured dispersion curves also agree reasonably well with the TB-LMTO calculations, although with some differences in the strength of the hybridization. In addition, the spectrum in the superconducting state revealed a 2 meV superconducting gap. The data also clearly show the presence of a coherent peak above the chemical potential μ, which originates from thermally excited electrons above the energy of 2Δ. This feature was not previously observed in the Lu-based material.