Abstract
We report on our investigation of the electronic structure of Ti$_2$O$_3$ using (hard) x-ray photoelectron and soft x-ray absorption spectroscopy. From the distinct satellite structures in the spectra we have been able to establish unambiguously that the Ti-Ti $c$-axis dimer in the corundum crystal structure is electronically present and forms an $a_{1g}a_{1g}$ molecular singlet in the low temperature insulating phase. Upon heating we observed a considerable spectral weight transfer to lower energies with orbital reconstruction. The insulator-metal transition may be viewed as a transition from a solid of isolated Ti-Ti molecules into a solid of electronically partially broken dimers where the Ti ions acquire additional hopping in the $a$-$b$ plane via the $e_g^{\pi}$ channel, the opening of which requires the consideration of the multiplet structure of the on-site Coulomb interaction.
Highlights
We report on our investigation of the electronic structure of Ti2O3 using x-ray photoelectron and soft x-ray absorption spectroscopy
Based on the presence of the c-axis V–V dimers in the corundum crystal structure of V2O3, Castellani et al [4] proposed a molecular singlet model for the a1g orbitals, projecting the system effectively onto a solid with S 1⁄4 1=2 entities, which should carry the essential physics for the metal-insulator transition (MIT) and the magnetic structure in the antiferromagnetic insulating phase
Field splitting so that the conductivity gap is opened [1,2]. This model is contradicted by band structure calculations, which showed that the overlap of the a1g and eπg orbitals can only be suppressed for an unrealistically short bond length [8]; i.e., Ti2O3 is a metal at all temperatures, with mixed a1g-eπg states for the c-axis dimer from the point of view of band theory [8,15]
Summary
We report on our investigation of the electronic structure of Ti2O3 using (hard) x-ray photoelectron and soft x-ray absorption spectroscopy. C-Axis Dimer and Its Electronic Breakup: The Insulator-to-Metal Transition in Ti2O3 This model is contradicted by band structure calculations, which showed that the overlap of the a1g and eπg orbitals can only be suppressed for an unrealistically short bond length [8]; i.e., Ti2O3 is a metal at all temperatures, with mixed a1g-eπg states for the c-axis dimer from the point of view of band theory [8,15].
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