Angle-resolved photoemission spectroscopy study of Fe(110) single crystal: Many-body interactions between quasi-particles at the Fermi level

A high-resolution angle-resolved photoemission spectroscopy (ARPES) study of Fe(110) single crystal was conducted to elucidate many-body interactions between quasi-particles at the Fermi level at low temperature. Two kink structures were observed in the energy-band dispersion at the binding energies of ~40 meV and ~270 meV for the bulk-derived band on the majority-spin Fermi surface around the Γ point. Based on analyses of the experimentally obtained real parts of the self-energy, these kink structures are derived from electron-phonon and electronmagnon interactions. The electronic structure of an itinerant ferromagnet iron has been studied extensively both theoretically [1-3] and experimentally [4-10]. Angle-resolved photoemission spectroscopy (ARPES), which is one of the most powerful methods to directly examine the energy-band and Fermi surface (FS) of solids [11], has already been applied to Fe single crystals [4-9]. Recently, the energy and angular resolution of ARPES has been drastically improved. It is now possible, by means of detailed spectral shape analyses, to estimate the real (ReΣ) and imaginary (ImΣ) parts of the selfenergy, and therefore study the underlying many-body interactions. Schäfer et al. examined the surface state of Fe(110) thin film grown on W(110) using high-resolution ARPES, and evaluated ReΣ and ImΣ [7]. They found electronic states are coupled to a bosonic mode with a characteristic cut-off energy at ~160 meV in the density-ofstates (DOS). On the basis of the inelastic neutron scattering results [10], it was claimed that the bosonic mode should be magnon. Furthermore, they undertook extensive FS mapping and concluded that the experimental Fermi velocities were much smaller than those given by the band-structure calculation [8]. This implies that strong renormalization exists near the Fermi level (EF) [8]. In order to elucidate many-body interactions between quasiparticles in the bulk-derived electronic states quantitatively, we carried out a high-resolution ARPES study using Fe(110) single crystal at low temperature, and examined in detail the majority-spin band on a FS surrounding the Γ point. We found two kink structures in the energy-band dispersion. The real part of the self-energy was experimentally determined. On the basis of the analyses of ReΣ, these two kink structures originate from the electron-phonon and electron-magnon