The $c$-axis dimer and its electronic break-up: the insulator-to-metal transition in Ti${}_2$O${}_3$

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.

arXiv comment7 pages, 4 figures

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Cited by in corpus (10)

• Charge-transfer effect in hard x-ray 1$s$ and 2$p$ photoemission spectra: LDA+DMFT and cluster-model analysis
• The role of defects in the metal-insulator transition in VO${}_2$ and V${}_2$O${}_3$
• Negative charge transfer energy in correlated compounds
• Tetramer Orbital-Ordering induced Lattice-Chirality in Ferrimagnetic, Polar MnTi2O4
• Satellites in the Ti~1$s$ core level spectra of SrTiO${}_3$ and TiO${}_2$
• Electronic band structure of Ti2O3 thin films studied by angle-resolved photoemission spectroscopy
• V 3$d$ charge and orbital states in V${}_2$OPO${}_4$ probed by x-ray absorption spectroscopy
• Giant orbital polarization of Ni${}^{2+}$ in square planar environment
• Surface-phase superconductivity in Mg-deficient V-doped MgTi${}_2$O${}_4$ spinel
• Linear dichroic x-ray absorption response of Ti-Ti dimers along the $c$ axis in Ti${}_2$O${}_3$ upon Mg substitution