Direct spectroscopic evidence for completely filled Cu $3d$ shell in BaCu$_2$As$_2$ and $\alpha$-BaCu$_2$Sb$_2

• Main Authors: Wu, S. F, Richard, P, van Roekeghem, A, Nie, S. M, Miao, H, Xu, N, Qian, T, Saparov, B, Fang, Z, Biermann, S, Sefat, Athena S, Ding, H
• Format: Journal Article
• Language: English
• Published: 01.04.2015
• Subjects: Physics - Strongly Correlated Electrons; Physics - Superconductivity
• DOI: 10.48550/arxiv.1504.00437

Phys. Rev. B 91, 235109 (2015) We use angle-resolved photoemission spectroscopy to extract the band dispersion and the Fermi surface of BaCu$_2$As$_2$ and $\alpha$-BaCu$_2$Sb$_2$. 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 BaCu$_2$As$_2$ 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 $\alpha$-BaCu$_2$Sb$_2$ without the pnictide-pnictide interlayer bonding characteristic of the collapsed tetragonal phase suggests that the short interlayer distance in BaCu$_2$As$_2$ follows from the stability of the Cu$^{+1}$ rather than the other way around. Our results confirm the prediction that BaCu$_2$As$_2$ is an $sp$ metal with weak electronic correlations.