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Pressure-induced orbital reordering in Na2CuF4

Craig I. Hiley1, Catriona A. Crawford1, Craig L. Bull2,3, Nicholas P. Funnell2, Urmimala Dey4,5, Nicholas C. Bristowe4, Richard I. Walton1,*, and Mark S. Senn1,†

  • *Contact author: r.i.walton@warwick.ac.uk
  • †Contact author: m.senn@warwick.ac.uk
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Phys. Rev. B 112, 035126 – Published 10 July, 2025

DOI: https://doi.org/10.1103/m265-k2p4

Abstract

The high-pressure behavior of Na2CuF4 is explored by powder neutron diffraction and density functional theory (DFT) calculations. A first-order phase transition is observed to take place between 2.4 and 2.9 GPa, involving a reorientation of the Jahn-Teller (JT) long axes of the [CuF6] octahedra (and therefore the dz2 Cu orbitals), in agreement with our DFT calculations which suggest a transition at ∼2.8 GPa. The transition can be described as being between a state of ferro-orbital order and one of A-type antiferro-orbital order, reflecting a shift in the associated electronic instability from being in the zone center to zone boundary of the first Brillouin zone of the parent structure. This change results in a decoupling of magnitude of the associated Jahn-Teller distortion of the Cu-F bond lengths from the lattice strain. This scenario is supported by our observations that the compressibility of the pretransition phase is highly anisotropic, while in the posttransition phase it becomes almost isotropic, and that we observed no further decrease of the magnitude the JT distortion up to 5 GPa, or melting of the orbital ordering in our DFT calculations up to at least 5 GPa.

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Phys. Rev. B 112, 035126– Published 10 July, 2025
  • Received 31 March 2025
  • Revised 22 May 2025
  • Accepted 24 June 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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