Direct observation of a Fermi surface and superconducting gap in LuNi2B2C

TL;DR

This study used ARPES to directly observe the Fermi surface and superconducting gap in LuNi2B2C, confirming theoretical predictions and revealing a 2meV gap and a previously unseen coherent peak.

Contribution

First direct ARPES measurement of the Fermi surface and superconducting gap in LuNi2B2C, with comparison to theoretical calculations and new observation of a coherent peak.

Findings

Fermi surface shows large parallel regions with nesting vector

Superconducting gap of approximately 2 meV observed

Coherent peak above the chemical potential detected

Abstract

We measured the Fermi surface (FS), band dispersion and superconducting gap in LuNi2B2C using Angle Resolved Photoemission Spectroscopy. Experimental data were compared with 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, albeit with some differences in the strength of the hybridization. In addition, the spectrum in the superconducting state revealed a 2meV superconducting gap. The data also clearly shows the presence of a coherent peak above the chemical potential, that originates from thermally excited electrons above the energy of 2 delta. This feature was not previously observed in the Lu-based material.