Abstract
Abstract BaBiO3 is an oxide perovskite with a wide variety of interesting properties. It was expected that the compound would behave like a metal. However, experiments revealed that BaBiO3 is not metallic, which started an extensive debate about the mechanism responsible for this insulating behavior. The two most important conjectures in this debate are charge disproportionation of the Bi ion into 3+ and 5+ cations and bond hybridization of the Bi 6s and O 2p orbitals. Both mechanisms induce a breathing mode of the oxygen octahedra, which is experimentally observed in single crystals and thin films. Recently, ultra-thin BaBiO3 films were studied with the aim of suppressing the breathing mode, which was expected to result in re-emergence of metallicity. However, this expectation was not confirmed so far. Furthermore, theoretical calculations predict that BaBiO3 becomes a topological insulator (TI) when doped with electrons. Since high-temperature superconductivity was observed when doping the compound with holes, an interface between a superconductor and a TI can be established within the same parent compound. In this Review, we discuss the theoretical and experimental findings concerning the mechanism responsible for the unexpected insulating behavior of BaBiO3 for both single crystals and thin films. An overview is given of the current state of the art and the experimental challenges of achieving an oxide topological insulating state in BaBiO3.
Highlights
The perovskite BaBiO3 was studied extensively in the last five decades, and it is receiving renewed attention
Using the linear augmented plane-wave (LAPW) method to calculate the band structure, Mattheiss and Hamann [13,14] predicted that a gap is formed in the band structure of BaBiO3 by a Fermi surface instability induced by the 6s-2p anti-bonding state
Xiao et al [67] studied the same transition-metal oxide systems with various materials. They found that LaOsO3, LaAgO3 and LaAuO3 sandwiched between LaAlO3 and SrIrO3 sandwiched between SrTiO3 are topological insulators
Summary
The perovskite BaBiO3 was studied extensively in the last five decades, and it is receiving renewed attention. In the search for the mechanism responsible for this insulating character of BaBiO3, researchers found that the compound becomes superconducting when doped with holes. The thin film studies mentioned above are important since BaBiO3 would only be applicable as a TI under the same conditions as those under which gating is possible. In this Review, we discuss the mechanism responsible for the insulating character in BaBiO3.
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