Cuprate-like orbital state in a metallic layered nickelate

June 28, 2017

In a study published in Nature Physics, researchers reported 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.

Spin states for a Ni d8+δ ion in a square-planar environment. The grey arrow represents a fractional occupancy determined by δ.

Scientific Achievement

We have discovered that the layered nickelate Pr₄Ni₃O₈ is metallic, with Ni 3^d states of x²-y² character that are hybridized with oxygen ligands.

Significance and Impact

Our result means that Pr₄Ni₃O₈ corresponds to the overdoped, metallic regime of the cuprates, and suggests electron doping as a route to a nickelate superconductor.

Research Details

X-ray absorption spectroscopy (XAS) establishes strong x²-y² Ni 3d-orbital polarization in bulk single crystals of R₄Ni₃O₈ (R=La, Pr).
DFT calculations corroborate XAS measurements to establish that Ni adopts a low-spin state with strong Ni 3d — O 2p hybridization.
While the related La₄Ni₃O₈ is a charge-ordered insulator, both transport and heat capacity data reveal that Pr₄Ni₃O₈ is metallic, a necessary condition for potential cuprate-like superconductivity.

DOI: 10.1038/nphys4149

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