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arXiv · 1710.08771

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

C. F. Chang·T. C. Koethe·Z. Hu·J. Weinen·S. Agrestini·J. Gegner·H. Ott·G. Panaccione·Hua Wu·M. W. Haverkort·H. Roth·A. C. Komarek·F. Offi·G. Monaco·Y. -F. Liao·K. -D. Tsuei·H. -J. Lin·C. T. Chen·A. Tanaka·L. H. Tjeng
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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.

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C. F. Chang, T. C. Koethe, Z. Hu, J. Weinen, S. Agrestini, J. Gegner, H. Ott, G. Panaccione, Hua Wu, M. W. Haverkort, H. Roth, A. C. Komarek, F. Offi, G. Monaco, Y. -F. Liao, K. -D. Tsuei, H. -J. Lin, C. T. Chen, A. Tanaka, L. H. Tjeng. 2017-10-24. The $c$-axis dimer and its electronic break-up: the insulator-to-metal transition in Ti$_2$O$_3$. https://doi.org/10.1103/physrevx.8.021004

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