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, and Tetsuya Ishikawa
Phys. Rev. B 87, 045108 – Published 9 January 2013

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 Tl2Ru2O7 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 (Eg160200 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 Hg2Ru2O7. The method is general for doping- and T-induced transitions and is valid for V2O3, CrN, La1xSrxMnO3, La2xSrxCuO4, etc. The obtained transition-metal–ligand (dp) bonding energies (V45–90 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.

  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
2 More
  • Received 28 October 2012

DOI:https://doi.org/10.1103/PhysRevB.87.045108

©2013 American Physical Society

Authors & Affiliations

Ashish Chainani1,2, Ayako Yamamoto3, Masaharu Matsunami4, Ritsuko Eguchi4, Munetaka Taguchi4, Yasutaka Takata1, Hidenori Takagi3, Shik Shin4, Yoshinori Nishino1, Makina Yabashi1, Kenji Tamasaku1, and Tetsuya Ishikawa1

  • 1Coherent X-ray Optics Laboratory, RIKEN Harima Institute, 1-1-1 Sayo-cho, Hyogo 679-5148 Japan
  • 2Department of Physics, Tohoku University, Aramaki, Aoba-ku, Sendai 980 8578 Japan
  • 3RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan
  • 4Excitation-order Research Team, RIKEN Harima Institute, 1-1-1 Sayo-cho, Hyogo 679-5148 Japan

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand
Issue

Vol. 87, Iss. 4 — 15 January 2013

Reuse & Permissions
Access Options
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review B

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×