Orbital-selective Mottness Driven by Geometric Frustration of Interorbital Hybridization in Pr4Ni3O10

The interplay among orbital-selective Mott physics, Hund’s coupling, tunable structural motifs, and Kondo-like scattering establishes a compelling paradigm for understanding and engineering correlated multi-orbital systems, as vividly exemplified by nickelate superconductors. Here, using high-resolution angle-resolved photoemission spectroscopy combined with theoretical calculations, we systematically investigate the electronic properties of trilayer nickelates. In La4Ni3O10, we observe pronounced interorbital hybridization, whereas in Pr4Ni3O10, the flat d_(z^2 ) band becomes markedly incoherent and diminishes in spectral weight. By contrast, the dispersive d_(x^2-y^2 ) bands retain coherence in both compounds. This striking incoherence/coherence dichotomy identifies an orbital-selective Mott phase modulated by the interlayer Ni-O-Ni bonding angle. The depletion of the d_(z^2 ) orbitals further frustrates the interorbital hybridization and influences the density-wave transition in Pr4Ni3O10. Moreover, the density-wave gap is substantially reduced in Pr4Ni3O10, likely due to extra scattering channels provided by the local moments of Pr3+ cations. Our findings elucidate the intricate interplay among lattice, orbital, spin, and electronic degrees of freedom and reveal a feasible structural control parameter for the multi-orbital correlated state in trilayer nickelates, which provide a concrete framework for understanding the emergence of superconductivity under high pressure.

💡 Research Summary

The authors combine high‑resolution angle‑resolved photoemission spectroscopy (ARPES) with density‑functional theory plus dynamical mean‑field theory (DFT+DMFT) to compare the electronic structures of the trilayer nickelates La₄Ni₃O₁₀ and Pr₄Ni₃O₁₀. Both compounds share the same Pmmm space group, but the smaller Pr³⁺ ion reduces the interlayer Ni‑O‑Ni bond angle from ~165° in the La compound to ~158° in the Pr compound, effectively applying chemical pressure and shortening the interlayer spacing. This structural change dramatically alters the hybridization between the Ni d_{z²} (flat) and d_{x²‑y²} (dispersive) orbitals.

In La₄Ni₃O₁₀ the d_{z²} flat band sits ~30 meV below the Fermi level and clearly hybridizes with the d_{x²‑y²} band, producing coherent quasiparticle peaks for both orbitals. By contrast, in Pr₄Ni₃O₁₀ the d_{z²} band loses most of its spectral weight and becomes incoherent, while the d_{x²‑y²} band remains sharp and well‑defined. This dichotomy signals an orbital‑selective Mott (OSM) phase in the Pr material, where only the d_{z²} orbital is driven toward localization.

DFT+DMFT calculations (U = 5 eV, J_H = 0.8 eV) reproduce these observations. They reveal that the flat d_{z²} states originate mainly from the outer Ni‑O layers and that decreasing the Ni‑O‑Ni angle suppresses their coherence. A hypothetical La₄Ni₃O₁₀ structure with the Pr bond angle yields a spectral function indistinguishable from real Pr₄Ni₃O₁₀, confirming that the bond angle is the key control knob. Moreover, the loss of d_{z²} coherence reduces screening for the d_{x²‑y²} electrons, enhancing their correlation and producing a “waterfall”‑like dispersion at lower binding energy in Pr₄Ni₃O₁₀.

Both compounds exhibit charge/spin‑density‑wave (DW) order, as evidenced by folding of the β Fermi‑surface pocket with a wave vector q_dw ≈ 0.62 b*. However, despite a higher DW transition temperature (T_dw ≈ 156 K) in Pr₄Ni₃O₁₀, the leading‑edge gap extracted from laser‑ARPES is only ~6 meV, roughly half the ~12 meV gap in La₄Ni₃O₁₀. The authors attribute the reduced gap to two intertwined effects: (i) the local magnetic moments of Pr³⁺ act as Kondo‑like scattering centers, disrupting phase coherence of the DW order, and (ii) the orbital‑selective incoherence of d_{z²} further frustrates interorbital hybridization, weakening the electronic instability that opens the gap.

Overall, the study demonstrates that a purely geometric parameter—the interlayer Ni‑O‑Ni bond angle—can tune the balance between itinerancy and localization in a multi‑orbital system, driving an orbital‑selective Mott phase, modifying density‑wave properties, and providing a structural pathway to the pressure‑induced superconductivity observed in Pr₄Ni₃O₁₀. The work also highlights parallels with iron‑based superconductors, where orbital‑selective correlations play a central role, suggesting a broader relevance of the findings to other correlated multi‑orbital materials.