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Direct Probe of Mott-Hubbard to Charge-Transfer Insulator Transition Print
Tuesday, 20 September 2011 11:08

Researchers report the most direct experimental verification of Mott-Hubbard and charge-transfer insulators using x-ray emission spectroscopy in transition-metal (TM) fluorides at Beamline The p-d hybridization features in the spectra allow a straightforward energy alignment of the anion-2p and metal-3d valence states, which visually shows the difference between the two types of insulators. Furthermore, in parallel with the theoretical Zaanen-Sawatzky-Allen diagram, complete experimental systematics of the 3d Coulomb interaction and the 2p-3d charge-transfer energy are reported and could serve as a universal experimental trend for other TM systems including oxides.



(Top) Schematic of (top) C-T and (bottom) M-H insulators. The lower intensity d-p and p-d humps are hybridization features in d- and p-partial DOS, respectively. Such features are evident in an MF2 system, enabling a straightforward alignment of the experimental partial DOS of TM-3d with F-2p. (Bottom) Experimental metal-3d and anion-2p valence states in MF2 aligned by EATH. (a) XES spectra of TM-Lα in red (gray) and F-Kα in blue (black) displays the partial 3d- and 2p-DOS, respectively. The arbitrary intensity of the TM-Lα and F-Kα spectra are scaled to the same maximum value for each component. Bars are LHBs indicated by the highest-energy TM-3d peaks from top valence states. From CrF2 to CuF2, TM-3d LHBs shifts toward lower energy, in parallel with the shrinking of the hybridization shoulder in F-Kα spectra.29 ZnF2 is the only C-T or intermediate insulator with Zn-3d under F-2p valence states. (b)–(d) show three amplified examples on the energy alignments.29 The leading edges of F-K and TM-Lα, the emission peaks of TM-Lα (F-K), and the hybridization features of F-K (TM-Lα), respectively, are aligned.

Work performed on ALS Beamline 8.0.1

Citation: Olalde-Velasco, P., J. Jimenez-Mier, J.D. Denlinger, Z. Hussain, and W.L. Yang, "Direct probe of Mott-Hubbard to charge-transfer insulator transition and electronic structure evolution in transition-metal systems," Physical Review B: Condensed Matter and Materials Physics 83 (24), 241102(R) (2011).