We use angle-resolved photoemission spectroscopy to extract the band dispersion and the Fermi surface of BaCu2As2 and α-BaCu2Sb2. While the Cu 3d bands in both materials are located around 3.5 eV below the Fermi level, the low-energy photoemission intensity mainly comes from As 4p states, suggesting a completely filled Cu 3d shell. The splitting of the As 3d core levels and the lack of pronounced three-dimensionality in the measured band structure of BaCu2As2 indicate a surface state likely induced by the cleavage of this material in the collapsed tetragonal phase, which is consistent with our observation of a Cu+1 oxydation state. However, the observation of Cu states at similar energy in α-BaCu2Sb2 without the pnictide-pnictide interlayer bonding characteristic of the collapsed tetragonal phase suggests that the short interlayer distance in BaCu2As2 follows from the stability of the Cu+1 rather than the other way around. Our results confirm the prediction that BaCu2As2 is an sp metal with weak electronic correlations.
@article{arxiv.1504.00437,
title = {Direct spectroscopic evidence for completely filled Cu $3d$ shell in BaCu$_2$As$_2$ and $\alpha$-BaCu$_2$Sb$_2$},
author = {S. F. Wu and P. Richard and A. van Roekeghem and S. M. Nie and H. Miao and N. Xu and T. Qian and B. Saparov and Z. Fang and S. Biermann and Athena S. Sefat and H. Ding},
journal= {arXiv preprint arXiv:1504.00437},
year = {2015}
}