Effect of electron correlations on photoemission from narrow-band metals

Abstract

Recent angle‐resolved photoemission measurements on Cu and Ni suggest the importance of electron correlations not included in band calculations. To study these effects, we have calculated the photoemission spectrum for the single‐band, strongly ferromagnetic Hubbard model. A hole in the ↑ band is viewed as a core hole which can hop from site to site. For a strong interaction U, a bound level exists below the ↓ band at the site of the spin ↑ hole. The photoemission spectrum consists of a main line (bound level occupied in final state) and a satellite (bound level unoccupied). The binding energy of the satellite is about U larger than that of the main line. The intensity of the main line is approximately n_↓, the fractional occupancy of the spin ↓ band. We identify the spin ↑ band (inferred from experiment) with the peak position of the main line as a function of the momentum k↘ transferred to the solid. The ratio of inferred band width to bare band width is approximately n_↓. Since the 3d‐bands are filled in Cu, no such band renormalization can occur for it. Strong electron correlations are also responsible for the small exchange splitting in Ni.