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Title: Large orbital polarization in a metallic square-planar nickelate

Abstract

High temperature cuprate superconductivity remains a defining problem in condensed matter physics.1,2 Among myriad approaches to addressing this problem has been the study of alternative transition metal oxides3,4 with similar structures and 3d electron count that are suggested as proxies for cuprate physics. Here, we report one such alternative: the low-valent, quasi-two-dimensional trilayer nickelates, R4Ni3O8 (R=La and Pr). By combining x-ray absorption spectroscopy and density functional theory calculations, we find that these compounds exhibit a low-spin configuration and significant orbital polarization of the unoccupied eg states with pronounced dx2-y2 character near the Fermi energy. Notably, a charge-ordered stripe phase, previously reported for La4Ni3O8,5 collapses in favor of a metallic ground state when substituting La with Pr, offering entrée to a region of 3d electron count important to hole-doped high-Tc cuprates but in the absence of quenched disorder.

Authors:
ORCiD logo; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division; National Science Foundation (NSF)
OSTI Identifier:
1395884
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nature Physics; Journal Volume: 13; Journal Issue: 9
Country of Publication:
United States
Language:
English

Citation Formats

Zhang, Junjie, Botana, A. S., Freeland, J. W., Phelan, D., Zheng, Hong, Pardo, V., Norman, M. R., and Mitchell, J. F.. Large orbital polarization in a metallic square-planar nickelate. United States: N. p., 2017. Web. doi:10.1038/NPHYS4149.
Zhang, Junjie, Botana, A. S., Freeland, J. W., Phelan, D., Zheng, Hong, Pardo, V., Norman, M. R., & Mitchell, J. F.. Large orbital polarization in a metallic square-planar nickelate. United States. doi:10.1038/NPHYS4149.
Zhang, Junjie, Botana, A. S., Freeland, J. W., Phelan, D., Zheng, Hong, Pardo, V., Norman, M. R., and Mitchell, J. F.. Mon . "Large orbital polarization in a metallic square-planar nickelate". United States. doi:10.1038/NPHYS4149.
@article{osti_1395884,
title = {Large orbital polarization in a metallic square-planar nickelate},
author = {Zhang, Junjie and Botana, A. S. and Freeland, J. W. and Phelan, D. and Zheng, Hong and Pardo, V. and Norman, M. R. and Mitchell, J. F.},
abstractNote = {High temperature cuprate superconductivity remains a defining problem in condensed matter physics.1,2 Among myriad approaches to addressing this problem has been the study of alternative transition metal oxides3,4 with similar structures and 3d electron count that are suggested as proxies for cuprate physics. Here, we report one such alternative: the low-valent, quasi-two-dimensional trilayer nickelates, R4Ni3O8 (R=La and Pr). By combining x-ray absorption spectroscopy and density functional theory calculations, we find that these compounds exhibit a low-spin configuration and significant orbital polarization of the unoccupied eg states with pronounced dx2-y2 character near the Fermi energy. Notably, a charge-ordered stripe phase, previously reported for La4Ni3O8,5 collapses in favor of a metallic ground state when substituting La with Pr, offering entrée to a region of 3d electron count important to hole-doped high-Tc cuprates but in the absence of quenched disorder.},
doi = {10.1038/NPHYS4149},
journal = {Nature Physics},
number = 9,
volume = 13,
place = {United States},
year = {Mon Jun 12 00:00:00 EDT 2017},
month = {Mon Jun 12 00:00:00 EDT 2017}
}
  • We used resonant inelastic x-ray scattering to investigate the electronic origin of orbital polarization in nickelate heterostructures taking LaTiO 3-LaNiO 3-3×(LaAlO 3), a system with exceptionally large polarization, as a model system. Furthermore, we find that heterostructuring generates only minor changes in the Ni 3d orbital energy levels, contradicting the often-invoked picture in which changes in orbital energy levels generate orbital polarization. Instead, O K-edge x-ray absorption spectroscopy demonstrates that orbital polarization is caused by an anisotropic reconstruction of the oxygen ligand hole states. This also provides an explanation for the limited success of theoretical predictions based on tuning orbitalmore » energy levels and implies that future theories should focus on anisotropic hybridization as the most effective means to drive large changes in electronic structure and realize novel emergent phenomena.« less
  • Nickel and palladium complexes of the type (M(L{sub 2}){sub 2})(BF{sub 4}){sub 2} and (M(L{sub 2})(L{sub 2}{prime}))(BF{sub 4}){sub 2} (where L{sub 2} and L{sub 2}{prime} are diphosphine ligands) have been synthesized. The lowest energy electronic absorption band for the nickel complexes decreases in energy as the bite size of the diphosphine ligand increases. Similarly, the half-wave potentials for the Ni(II/I) and Pd(II/O) couples become more positive as the bite size increases. Structural studies of (Ni(dppm){sub 2})(BF{sub 4}){sub 2} (where dppm is bis(diphenylphosphino)methane) and (Ni-(dppb){sub 2})(PF{sub 6}){sub 2} (where dppb is 1,2-bis(diphenylphosphino)benzene) show that increasing the bite size of the diphosphine ligandsmore » results in larger tetrahedral distortions. The crystal structure of (Ni(Dppm){sub 2})(BF{sub 4}){sub 2}(C{sub 50}H{sub 44}B{sub 2}F{sub 8}NiP{sub 4}) and (Ni(Dppb){sub 2})(PF{sub 6}){sub 2}(C{sub 74}H{sub 64}F{sub 12}NiP{sub 6}) were measured and are reported herein. Calculations made using the extended Huckel theory indicate that the observed distortions may have an electronic as well as a steric component. The calculations also allow rationalization of the electronic absorption spectra, electrochemical data, and the stability of the Ni(I) and Pd(I) complexes (Ni(dppp){sub 2})(BF{sub 4}) (where dppp is 1,3-bis(diphenylphosphino)propane) and (Pd(dppx){sub 2})(BF{sub 4}) (where dppx is {alpha},{alpha}{prime}-bis(diphenylphosphino)-o-xylene). Complexes containing the ligand dppm have a marked tendency to become five-coordinate, as indicated by the structural determination of (Ni(dppm){sub 2}(CH{sub 3}CN))(PF{sub 6}){sub 2}. The crystal structure for the latter complex is reported.« less
  • An analysis of the Ce ({ital n}{sub {ital f}}{similar_to}1) 4{ital f} states within the perturbation theory around the atomic limit is also performed both within the Hubbard I approximation as well as within the strong-coupling mean-field approximation. The Hubbard I solution shows that when the {ital f}-electron number deviates slightly from 1 the energy difference between the OP and the paramagnetic metallic state is very small. In this analysis we show that the Hubbard {ital U} does not enter the criterion for OP. The reason for this is that in both phases the lower Hubbard band is occupied while themore » upper one gives only a small difference in the kinetic energy. The SCMFA improves the Hubbard I solution, taking into account exchangelike shifts of the centers of the bands. In this analysis we find that at a filling larger than the critical one ({ital n}{congruent}1.07) the ground state is a Pauli paramagnet, while at smaller fillings the orbital polarized solution has lower energy.« less