Article

Large orbital polarization in a metallic square-planar nickelate

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Abstract

High-temperature cuprate superconductivity remains a defining problem in condensed-matter physics. Among myriad approaches to addressing this problem has been the study of alternative transition metal oxides with similar structures and 3d electron count that are suggested as proxies for cuprate physics. None of these analogues has been superconducting, and few are even metallic. Here, we report that the low-valent, quasi-two-dimensional trilayer compound Pr4Ni3O8 avoids a charge-stripe-ordered phase previously reported for La4Ni3O8, leading to a metallic ground state. X-ray absorption spectroscopy shows that metallic Pr4Ni3O8 exhibits a low-spin configuration with significant orbital polarization and pronounced dx2y2 character in the unoccupied states above the Fermi energy, a hallmark of the cuprate superconductors. Density functional theory calculations corroborate this finding, and reveal that the dx2y2 orbital dominates the near-Ef occupied states as well. Belonging to a regime of 3d electron count found for hole-doped cuprates, Pr4Ni3O8 thus represents one of the closest analogues to cuprates yet reported and a singularly promising candidate for high-Tc superconductivity if electron doping could be achieved.

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Acknowledgements

Crystal growth, characterization, and theoretical calculations were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. V.P. acknowledges support from X. de Galicia via EM2013/037 and MINECO through MAT2013-44673-R and Ramon y Cajal Program under Grant no. RyC2011-09024. ChemMatCARS Sector 15 is supported by the National Science Foundation under grant number NSF/CHE-1346572. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. The authors thank Y.-S. Chen for his help with single-crystal X-ray diffraction at 15-ID-B, S. Lapidus for his help with the high-resolution X-ray powder diffraction at 11-BM, and W. E. Pickett, Y.-S. Chen and Y. Ren for helpful discussions.

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Affiliations

  1. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

    • Junjie Zhang
    • , A. S. Botana
    • , D. Phelan
    • , Hong Zheng
    • , M. R. Norman
    •  & J. F. Mitchell
  2. Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA

    • J. W. Freeland
  3. Departamento de Fisica Aplicada, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain

    • V. Pardo
  4. Instituto de Investigacions Tecnoloxicas, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain

    • V. Pardo

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Contributions

J.F.M. and J.Z. directed the project. J.Z. and H.Z. grew single crystals. J.Z. and D.P. performed the transport measurements. J.Z. performed the powder and single-crystal synchrotron X-ray diffraction experiments. J.W.F. and J.Z. performed the XAS experiments. J.W.F., J.Z. and M.R.N. analysed data. A.S.B. and V.P. performed DFT calculations. J.Z., A.S.B., J.W.F. and J.F.M. wrote the manuscript, with contributions from all coauthors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Junjie Zhang.

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