Linear-response description of superexchange-driven orbital ordering in K2CuF4

Julian Musshoff, Guoren Zhang, Erik Koch, and Eva Pavarini
Phys. Rev. B 100, 045116 – Published 12 July 2019

Abstract

We study the nature of orbital and magnetic order in the layered perovskite K2CuF4, and compare to the case of the infinite-layer system KCuF3. To this end, we augment the local-density approximation + dynamical mean-field theory technique with linear-response functions. We explain orbital and magnetic order, and their evolution with increasing pressure. We show that both the tetragonal (ɛT) and the Jahn-Teller (ɛJT) crystal-field splitting play a key role. We find that surprisingly, unlike in KCuF3,ɛT is comparable to, or even larger than, ɛJT; in addition, ɛT is mostly determined by the layered structure itself and by the compression of the K cage, rather than by the deformations of the CuF6 octahedra. Next, we study the nature of orbital order. We calculate the superexchange transition temperature, finding TKK300K, a value close to the one for KCuF3. Thus, in K2CuF4 as in KCuF3,TKK is too small to explain the existence of orbital order up to the melting temperature. We show, however, that in the case of the layered perovskite, an additional superexchange mechanism is at work. It is an orbital Zeeman term, ĥKK, and it is active also above TKK. We show that due to ĥKK, phases with different types of ordering can coexist at temperatures below TKK. Similar effects are likely to play a role in other layered correlated systems.

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  • Received 15 May 2019
  • Revised 17 June 2019

DOI:https://doi.org/10.1103/PhysRevB.100.045116

©2019 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Julian Musshoff1,2, Guoren Zhang3, Erik Koch1, and Eva Pavarini1

  • 1Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany
  • 2Department of Physics, RWTH Aachen University, 52074 Aachen, Germany
  • 3Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China

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Vol. 100, Iss. 4 — 15 July 2019

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