Electronic structure of the Kagomé lattice compound Rb₂Ni₃S₄

We have studied the electronic structure of the layered Kogomé lattice compound Rb₂Ni₃S₄by photoemission spectroscopy and comparison of the results with band-structure and configuration-interaction cluster-model calculations. The band-structure calculation reproduced the gross features of the experimental spectra but could not reproduce the weak satellite feature, and predicted the narrow peak of Ni 3d character just below the Fermi level(E_F)to be too strong. On the other hand, the cluster-model calculation assuming the low-spin (S=0)ground state reproduced the satellite but failed to predict the same peak just below E_Fat the correct energy position. Angle-resolved photoemission measurements revealed momentum dispersions for the S 3p-derived and Ni 3d-S 3p hybridized bands, in agreement with the band-structure calculation, whereas the Ni 3d-derived band just below E_Fwas found to be dispersionless, unlike the result of the band-structure calculation. We conclude that Rb₂Ni₃S₄is a moderately correlated, strongly p-d hybridized system.