The nature of the two-peak structure in NiO valence band photoemission

Abstract

In spite of extensive studies on NiO and their accomplishments, the rich physics still raises unsolved physical problems. In particular, the nature of the two-peak structure in the valence band photoemission spectra is still controversial. By using \textit{ab initio} LQSGW+DMFT, the two-peak structure is shown to be driven by the concerted effect of antiferromagnetic ordering and intersite electron hopping. Magnetic ordering in the Ni-$e_{g}$ orbitals splits majority- and minority-spin Ni-$t_{2g}$ levels due to local Hund's coupling. Strong hybridization between O-$p$ and Ni-$e_g$, a signature of the Zhang-Rice bound state formation, boosts oxygen-mediated intersite Ni-$e_g$ orbital hopping, resulting in the enhancement of majority-spin Ni $t_{2g}$-$e_{g}$ splitting. Interestingly, these two splittings of distinct physical origins match and give rise to the observed two-peak structure in NiO. Our new understanding should be useful in designing advanced devices based on the NiO for the hole transport.