Fermi surface of Co(0001) and initial-state linewidths determined by soft x-ray angle-resolved photoemission spectroscopy

Abstract

Soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) reveals the band dispersion and Fermi surface of bulk ferromagnetic Co(0001). The spectral peak widths are narrower than previously observed in low-energy ARPES experiments. From very general considerations and in contrast to low-energy experiments, we show that the final-state broadening is significantly reduced in the experimentally measured linewidth. SX-ARPES yields the intrinsic initial-state lifetime ${\ensuremath{\Gamma}}_{i}=1/2{\ensuremath{\Sigma}}_{i}(\stackrel{P\vec}{k},E)$, the latter being the initial state self-energy, quantifying the correlations and indicating an energy and momentum dependence. Our results open a way to a direct measurement of the many-particle effects in solid-state physics, which does not require a modeling of the final state and provides a genuine description of the initial state.