Weakness of Correlation Effect Manifestation in BaNi2As2: An ARPES and LDA plus DMFT Study

The electronic spectral function of BaNi2As2 is investigated using both angle-resolved photoemission spectroscopy (ARPES) and a combined computational scheme of local density approximation and dynamical mean-field theory (LDA + DMFT). In contrast to the well-studied isostructural iron arsenide high-temperature superconductors, BaNi2As2 demonstrates weak correlation effects, although Ni 3d electrons have an even larger on-site interaction than Fe 3d electrons. The LDA + DMFT effective mass enhancement for bands crossing the Fermi level is found to be only about 1.2, which agrees well with ARPES data. This reduction of the correlation manifestation with respect to iron pnictides comes from the increase of 3d-orbital filling when going from Fe to Ni. The electron correlations cause a remarkable reconstruction of the bare BaNi2As2 LDA band structure below -0.8 eV due to a self-energy effect. A simplified toy model to understand the weakness of correlation effects in BaNi2As2 and to describe the LDA + DMFT self-energy shape is discussed. For a more realistic comparison of LDA + DMFT spectral function maps with ARPES data, we take into account several experimental features: the photoemission cross section, the experimental energy and angular resolutions, and the photo-hole lifetime effects. Thus, the LDA + DMFT calculations presented here with experimental features provide a nearly qualitative agreement with ARPES data and assure the observation of an apparent dramatic decrease of the correlation strength compared to the Fe compounds.