Electronic structure evolution across the peierls metal-insulator transition in a correlated ferromagnet

P. A. Bhobe, A. Kumar, M. Taguchi, R. Eguchi, M. Matsunami, Y. Takata, A. K. Nandy, P. Mahadevan, D. D. Sarma, A. Neroni, E. Şaşioğlu, M. Ležaić, M. Oura, Y. Senba, H. Ohashi, K. Ishizaka, M. Okawa, S. Shin, K. Tamasaku, Y. KohmuraM. Yabashi, T. Ishikawa, K. Hasegawa, M. Isobe, Y. Ueda, A. Chainani

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Abstract

Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K2Cr8O16, which exhibits a temperature-dependent (T-dependent) paramagnetic-toferromagnetic- metal transition at TC = 180 K and transforms into a ferromagnetic insulator below TMI = 95 K. We observe clear T-dependent dynamic valence (charge) fluctuations from above TC to TMI, which effectively get pinned to an average nominal valence of Cr+3.75 (Cr4+:Cr3+ states in a 3:1 ratio) in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0) ~ 3.5(kBTMI) ~ 35 meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U ~ 4 eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr) and the half-metallic ferromagnetism in the t2g up-spin band favor a low-energy Peierls metal-insulator transition.

Original languageEnglish
Article number041004
JournalPhysical Review X
Volume5
Issue number4
DOIs
Publication statusPublished - 2015

Keywords

  • Condensed matter physics

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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    Bhobe, P. A., Kumar, A., Taguchi, M., Eguchi, R., Matsunami, M., Takata, Y., Nandy, A. K., Mahadevan, P., Sarma, D. D., Neroni, A., Şaşioğlu, E., Ležaić, M., Oura, M., Senba, Y., Ohashi, H., Ishizaka, K., Okawa, M., Shin, S., Tamasaku, K., ... Chainani, A. (2015). Electronic structure evolution across the peierls metal-insulator transition in a correlated ferromagnet. Physical Review X, 5(4), [041004]. https://doi.org/10.1103/PhysRevX.5.041004