Electronic structure and correlation of La₄Co₂NiO₈Cl₂: a theoretical proposal for a La₄Ni₃O₁₀-like high-temperature superconductor

Summary

Building on the discovery of high-pressure superconductivity in trilayer nickelate La₄Ni₃O₁₀, this study employed density functional theory combined with dynamical mean-field theory (DFT+DMFT) to design and calculate the cobalt-based analogue La₄Co₂NiO₈Cl₂. B_y substituting the inner-layer Co in the high-pressure phase La₄Co₃O₁₀ with Ni and incorporating Cl to achieve electron doping, this compound acquires a crystal structure and strongly correlated electronic characteristics similar to those of superconducting La₄Ni₃O₁₀: the outer-layer Co orbitals exhibit strong effective mass enhancement and non-Fermi liquid behavior, while the inner-layer Ni behaves as a weakly correlated Fermi liquid; a flat band near the Fermi level originating from the outer-layer Co orbitals emerges around the M point; and there is pronounced orbital selectivity as well as local spin fluctuations mixing high-spin and low-spin states. These features are in close agreement with the key electronic states of La₄Ni₃O₁₀, indicating that La₄Co₂NiO₈Cl₂ is a promising candidate for realizing high-temperature superconductivity in cobalt-based layered compounds, providing a theoretical basis for subsequent experimental exploration.

Materials

• La₄Co₂NiO₈Cl₂
• La₄Ni₃O₁₀

Methods

• Density functional theory + dynamical mean-field theory (DFT+DMFT)

Keywords

• orbital selectivity
• hund's metal
• flat bands
• non fermi liquid
• layer dependent correlation

Highlights

• This work establishes La₄Co₂NiO₈Cl₂ as a promising candidate for hosting high-temperature superconductivity in cobalt-based layered compounds.
• Provides a theoretical basis for future experimental exploration of Co-based analogs.

Conclusions

• La₄Co₂NiO₈Cl₂ exhibits electronic structure and correlation strength similar to those of superconducting La₄Ni₃O₁₀.
• The outer-layer Co orbitals exhibit strong effective mass enhancement and non-Fermi liquid behavior, while the inner-layer Ni behaves as a weakly correlated Fermi liquid.
• A flat band near the Fermi level originating from the outer-layer Co orbitals emerges around the M point.
• Pronounced orbital selectivity and local spin fluctuations mixing high-spin and low-spin states are present.

Main claims

• La₄Co₂NiO₈Cl₂ exhibits a crystal structure and strongly correlated electronic characteristics similar to those of superconducting La₄Ni₃O₁₀, including layer-dependent correlation and flat bands near the Fermi level.
  • Evidence: Abstract: 'this compound acquires a crystal structure and strongly correlated electronic characteristics similar to those of superconducting La₄Ni₃O₁₀'
• The strong correlation character resides in the outer-layer Co sites, suggesting Co can play an active role in unconventional superconductivity.
  • Evidence: Abstract: 'the outer-layer Co orbitals exhibit strong effective mass enhancement and non-Fermi liquid behavior' and Discussion: 'the outer-layer Co sites host the strong correlation essential for superconductivity'

Workflow

• Structural optimization
  • Materials: La₄Co₂NiO₈Cl₂ based on high-pressure La₄Ni₃O₁₀ structure
  • Methods: DFT (VASP) with GGA-PBE
  • Observations: Optimized lattice parameters: a=b=3.6116 Å, c=26.0039 Å
• Electronic structure calculation — La₄Co₂NiO₈Cl₂ exhibits electronic structure similar to La₄Ni₃O₁₀
  • Materials: Optimized structure
  • Methods: DFT+DMFT (eDMFT, WIEN₂K); CT-QMC solver at 290K
  • Observations: Outer-layer Co shows strong effective mass enhancement and non-Fermi liquid behavior; Inner-layer Ni is weakly correlated Fermi liquid
• Analysis of superconductivity indicators — La₄Co₂NiO₈Cl₂ is a promising candidate for high-temperature superconductivity
  • Materials: DFT+DMFT results
  • Methods: Self-energy analysis; Spectral functions; Local multiplet weights
  • Observations: Flat bands near Fermi level at M point; Orbital selectivity; Mixed high-spin and low-spin states