Momentum-Resolved Electronic Structure of the High-TcSuperconductor Parent CompoundBaBiO3

Abstract

We investigate the band structure of BaBiO_{3}, an insulating parent compound of doped high-T_{c} superconductors, using in situ angle-resolved photoemission spectroscopy on thin films. The data compare favorably overall with density functional theory calculations within the local density approximation, demonstrating that electron correlations are weak. The bands exhibit Brillouin zone folding consistent with known BiO_{6} breathing distortions. Though the distortions are often thought to coincide with Bi^{3+}/Bi^{5+} charge ordering, core level spectra show that bismuth is monovalent. We further demonstrate that the bands closest to the Fermi level are primarily oxygen derived, while the bismuth 6s states mostly contribute to dispersive bands at deeper binding energy. The results support a model of Bi-O charge transfer in which hole pairs are localized on combinations of the O 2p orbitals.

Valence transition model of the pseudogap, charge order, and superconductivity in electron-doped and hole-doped copper oxides

“…Interestingly, an early theory of the metal-insulator transition 43 in (RE)NiO 3 is very closely related to the neutral-ionic transition model. Finally, lower than formal charge has also been recognized recently in the perovskite BaBiO 3 , where again the true electron configuration of the Bi-ions is a homogenous Bi 3+ , as opposed to what was believed before, alternating Bi 3+ and Bi 5+ ions 47,48 . We will not only be interested in when negative charge-transfer gap is most likely, but whether there can occur a real transition from positive to negative charge-transfer gap.…”

“…Then for |∆| > U d the system is a Mott-Hubbard insulator, for |∆| < U d the system is a charge-transfer insulator 32 . Note that the system remains a charge-transfer insulator even if the sign of ∆ is negative 41,42,44,47 . We will not only be interested in when this is most likely, but whether there can occur a real transition from positive to negative ∆.…”

“…An alternate approach to SC is suggested by recent theoretical and experimental work that have determined that undoped BaBiO 3 is a negative charge-transfer gap material, with monovalent Bi ions, the Fermi level lying predominantly on O-based orbitals, and Bi 6s orbitals significantly lower in energy 47,48 . It has been suggested that SC is due to hole pairs on oxygens, as had been suggested also in the earlier version of this work 31 .…”

“…We believe that the need to go beyond existing theories arises from the following fundamental question, viz., why is SC in Ba 1−x K x BiO 3 limited to a relatively narrow dopant concentration 47,199 , 0.37 < x < 0.5? The answer to this question is obtained by simple counting of charge carriers.…”

Transformation of Perovskite BaBiO3 into Layered BaBiO2.5 Crystals Featuring Unusual Chemical Bonding and Luminescence

“…[6][7][8] Among Bi-containing oxides, perovskite BaBiO 3 ,i nw hich octahedral [BiO 6 ]b reathes out and in for Bi 3 + and Bi 5 + ,r espectively,h as long been investigated. [9][10][11] Previous investigationsh ave shown that under hole-doping conditions, such as in Ba 0.6 K 0.4 BiO 3 and BaBi 0.7 Pb 0.3 O 3 ,the breathing distortion is significantly suppressed, and this leads to as imple perovskite lattice in which superconductivity emerges. [12,13] In essence, such compositional engineering results in the modification of coordination environments of cations in the framework.…”