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Electronic Structure Evolution across the Peierls Metal-Insulator Transition in a Correlated Ferromagnet

Bhobe, PA and Kumar, A and Taguchi, M and Eguchi, R and Matsunami, M and Takata, Y and Nandy, AK and Mahadevan, P and Sarma, DD and Neroni, A and Sasioglu, E and Lezaic, M and Oura, M and Senba, Y and Ohashi, H and Ishizaka, K and Okawa, M and Shin, S and Tamasaku, K and Kohmura, Y and Yabashi, M and Ishikawa, T and Hasegawa, K and Isobe, M and Ueda, Y and Chainani, A (2015) Electronic Structure Evolution across the Peierls Metal-Insulator Transition in a Correlated Ferromagnet. In: PHYSICAL REVIEW X, 5 (4).

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Official URL: http://dx.doi.org/10.1103/PhysRevX.5.041004

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-to-ferromagnetic- metal transition at T-C = 180 K and transforms into a ferromagnetic insulator below T-MI = 95 K. We observe clear T-dependent dynamic valence (charge) fluctuations from above T-C to T-MI, 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) similar to 3.5(k(B)T(MI)) similar to 35 meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U similar to 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 t(2g) up-spin band favor a low-energy Peierls metal-insulator transition.

Item Type: Journal Article
Additional Information: Copy right for this article belongs to the AMER PHYSICAL SOC, ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Depositing User: Id for Latest eprints
Date Deposited: 31 Oct 2015 06:00
Last Modified: 31 Oct 2015 06:00
URI: http://eprints.iisc.ac.in/id/eprint/52632

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