[Paper Review] Electronic structure of the alternating monolayer-trilayer phase of La3Ni2O7

Sebastien N. Abadi, Ke-Jun Xu+13 more|arXiv (Cornell University)|Feb 11, 2024

Inorganic Chemistry and Materials6 citations

TL;DR

The paper uses ARPES to study the 1313 alternating monolayer-trilayer La3Ni2O7 phase, revealing a flat band, an extra electron pocket, and notable Ni d-band renormalizations compared with LDA calculations.

ABSTRACT

Recent studies of La$_3$Ni$_2$O$_7$ have identified a bilayer (2222) structure and an unexpected alternating monolayer-trilayer (1313) structure, both of which feature signatures of superconductivity near 80 K under high pressures. Using angle-resolved photoemission spectroscopy, we measure the electronic structure of 1313 samples. In contrast to the previously studied 2222 structure, we find that the 1313 structure hosts a flat band with a markedly different binding energy, as well as an additional electron pocket and band splittings. By comparison to local-density approximation calculations, we find renormalizations of the Ni-$d_{z^2}$ and Ni-$d_{x^2-y^2}$ derived bands to be about 5 to 7 and about 4 respectively, suggesting strong correlation effects. These results reveal important differences in the electronic structure brought about by the distinct structural motifs with the same stoichiometry. Such differences may be relevant to the putative high temperature superconductivity.

Motivation & Objective

• Motivate understanding of how alternating monolayer-trilayer (1313) structure affects electronic structure in La3Ni2O7 compared to the bilayer (2222) structure.
• Characterize the electronic structure of 1313 via angle-resolved photoemission spectroscopy (ARPES).
• Compare experimental results to local-density approximation (LDA) calculations and assess correlation effects on Ni d bands.

Proposed method

• Perform ARPES measurements on 1313 La3Ni2O7 samples to map electronic structure and band dispersions.
• Compare ARPES results with LDA calculations to identify renormalizations of Ni d-band-derived states.
• Identify and characterize features such as flat bands, electron pockets, and band splittings (γ, δ, β bands).
• Note evolution of band structure when moving from LDA+U to LDA in calculations (as reported).

Experimental results

Research questions

• RQ1 What are the characteristic electronic structure features of the 1313 La3Ni2O7 phase as observed by ARPES?
• RQ2 How does the 1313 structure differ from the previously studied 2222 structure in electronic structure?
• RQ3 What renormalization factors modify Ni d-band dispersions relative to LDA predictions, and what do they imply about correlation effects?
• RQ4 Do flat bands, electron pockets, and multilayer splitting appear in the 1313 phase, and where are they located in momentum space?

Key findings

• The 1313 phase hosts a flat band with a distinct binding energy.
• An additional electron pocket is observed in the 1313 phase.
• Band splittings (multilayer effects) are detected in the flat band and large cuprate-like pockets.
• Renormalizations of Ni dz2 and d(x2−y2) derived bands are about 5–7 and ~4, respectively.
• LDA calculations (not LDA+U) are used for comparison, highlighting strong correlation effects in the Ni-derived bands.
• Structural motifs with the same stoichiometry yield important electronic-structure differences relevant to potential high-temperature superconductivity.