High-resolution photoemission study of ZrZn₂

We have performed high-resolution ultraviolet photoemission spectroscopy on a weak itinerant ferromagnet ZrZn₂ (ferromagnetic transition temperature TCurie=28 K), whose superconductivity with Tc=0.29 K has been recently reported [Pfleiderer, et al., Nature 412 (2001) 58]. We have successfully determined the density of states (DOS) in the valence-band and near EF region. The mass-enhancement factor estimated from the present experiment is about 5, suggesting a strong coupling of electrons with a spin fluctuation and/or phonons. This implies that heavy quasi-particle bands in the vicinity of EF play an important role for the occurrence of the ferromagnetism and the superconductivity in ZrZn₂. Although the band calculation predicts the exchange splitting being 70-90 meV, we have observed negligible change in the photoemission spectrum near EF even across TCurie within our energy resolution (7 meV). This suggests that the actual exchange splitting is much smaller and/or the size of the exchange splitting is significantly different for different bands.