Quantifying covalency and metallicity in correlated compounds undergoing metal-insulator transitions

Ashish Chainani, Ayako Yamamoto, Masaharu Matsunami, Ritsuko Eguchi, Munetaka Taguchi, Yasutaka Takata, Hidenori Takagi, Shik Shin, Yoshinori Nishino, Makina Yabashi, Kenji Tamasaku, Tetsuya Ishikawa

Research output: Contribution to journalArticle

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Abstract

The tunability of bonding character in transition-metal compounds controls phase transitions and their fascinating properties such as high-temperature superconductivity, colossal magnetoresistance, spin-charge ordering, etc. However, separating out and quantifying the roles of covalency and metallicity derived from the same set of transition-metal d and ligand p electrons remains a fundamental challenge. In this study, we use bulk-sensitive photoelectron spectroscopy and configuration-interaction calculations for quantifying the covalency and metallicity in correlated compounds. The method is applied to study the first-order temperature- (T-) dependent metal-insulator transitions (MITs) in the cubic pyrochlore ruthenates Tl2Ru2O 7 and Hg2Ru2O7. Core-level spectroscopy shows drastic T-dependent modifications which are well explained by including ligand-screening and metallic-screening channels. The core-level metallic-origin features get quenched upon gap formation in valence band spectra, while ionic and covalent components remain intact across the MIT. The results establish temperature-driven Mott-Hubbard MITs in three-dimensional ruthenates and reveal three energy scales: (a) 4d electronic changes occur on the largest (∼eV) energy scale, (b) the band-gap energies/charge gaps (Eg∼160-200 meV) are intermediate, and (c) the lowest-energy scale corresponds to the transition temperature TMIT (∼10 meV), which is also the spin gap energy of Tl2Ru2O7 and the magnetic-ordering temperature of Hg2Ru2O 7. The method is general for doping- and T-induced transitions and is valid for V2O3, CrN, La1-xSr xMnO3, La2-xSrxCuO4, etc. The obtained transition-metal-ligand (d-p) bonding energies (V∼45-90 kcal/mol) are consistent with thermochemical data, and with energies of typical heteronuclear covalent bonds such as C-H, C-O, C-N, etc. In contrast, the metallic-screening energies of correlated compounds form a weaker class (V *∼10-40 kcal/mol) but are still stronger than van der Waals and hydrogen bonding. The results identify and quantify the roles of covalency and metallicity in 3d and 4d correlated compounds undergoing metal-insulator transitions.

Original languageEnglish
Article number045108
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume87
Issue number4
DOIs
Publication statusPublished - 2013 Jan 9
Externally publishedYes

Fingerprint

Metal insulator transition
metal compounds
metallicity
insulators
Screening
Core levels
Ligands
Transition metals
Energy gap
screening
transition metals
Colossal magnetoresistance
Transition metal compounds
Temperature
ligands
Covalent bonds
energy
Photoelectron spectroscopy
Valence bands
Superconductivity

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electronic, Optical and Magnetic Materials

Cite this

Quantifying covalency and metallicity in correlated compounds undergoing metal-insulator transitions. / Chainani, Ashish; Yamamoto, Ayako; Matsunami, Masaharu; Eguchi, Ritsuko; Taguchi, Munetaka; Takata, Yasutaka; Takagi, Hidenori; Shin, Shik; Nishino, Yoshinori; Yabashi, Makina; Tamasaku, Kenji; Ishikawa, Tetsuya.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 87, No. 4, 045108, 09.01.2013.

Research output: Contribution to journalArticle

Chainani, A, Yamamoto, A, Matsunami, M, Eguchi, R, Taguchi, M, Takata, Y, Takagi, H, Shin, S, Nishino, Y, Yabashi, M, Tamasaku, K & Ishikawa, T 2013, 'Quantifying covalency and metallicity in correlated compounds undergoing metal-insulator transitions', Physical Review B - Condensed Matter and Materials Physics, vol. 87, no. 4, 045108. https://doi.org/10.1103/PhysRevB.87.045108
Chainani, Ashish ; Yamamoto, Ayako ; Matsunami, Masaharu ; Eguchi, Ritsuko ; Taguchi, Munetaka ; Takata, Yasutaka ; Takagi, Hidenori ; Shin, Shik ; Nishino, Yoshinori ; Yabashi, Makina ; Tamasaku, Kenji ; Ishikawa, Tetsuya. / Quantifying covalency and metallicity in correlated compounds undergoing metal-insulator transitions. In: Physical Review B - Condensed Matter and Materials Physics. 2013 ; Vol. 87, No. 4.
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