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 mu, which originates from thermally excited electrons above the energy of 2 Delta. This feature was not previously observed in the Lu-based material.