[Paper Review] Electronic Structure of Superconducting Infinite-Layer Lanthanum Nickelates

Wenjie Sun, Zhicheng Jiang+13 more|arXiv (Cornell University)|Mar 12, 2024

Magnetic and transport properties of perovskites and related materials4 citations

TL;DR

This study presents the first angle-resolved photoemission spectroscopy (ARPES) of superconducting infinite-layer La0.8Sr0.2NiO2 films, revealing a momentum-resolved electronic structure with a 3D electron pocket and strong mass enhancement (m*/m_DFT ≈ 2–3) in Ni-dx²−y²-derived bands. The observed band dispersion anomalies resemble cuprate-like kinks and waterfall features, providing critical insights into the unconventional superconductivity in nickelates.

ABSTRACT

Revealing the momentum-resolved electronic structure of infinite-layer nickelates is essential for understanding this new class of unconventional superconductors, but has been hindered by the formidable challenges in improving the sample quality. In this work, we report for the first time the angle-resolved photoemission spectroscopy of superconducting La$_{0.8}$Sr$_{0.2}$NiO$_{2}$ films prepared by molecular beam epitaxy and ${\mathrm{ extit{in situ}}}$ atomic-hydrogen reduction. The measured Fermi topology closely matches theoretical calculations, showing a large Ni-$d_{x^2-y^2}$ derived Fermi sheet that evolves from hole-like to electron-like along $k_{z}$, and a three-dimensional (3D) electron pocket centered at Brillouin zone corner. The Ni-$d_{x^2-y^2}$ derived bands show a mass enhancement ($m^*/m_{ m{DFT}}$) of 2-3,while the 3D electron band shows negligible band renormalization. Moreover, the Ni-$d_{x^2-y^2}$ derived states also display a band dispersion anomaly at higher binding energy, reminiscent of the waterfall feature and kinks observed in cuprates.

Motivation & Objective

• To resolve the momentum-resolved electronic structure of superconducting infinite-layer nickelates, a key class of unconventional superconductors.
• To overcome the longstanding challenge of sample quality that has hindered direct electronic structure measurements in these materials.
• To establish a direct link between experimental observations and theoretical predictions of the Fermi surface topology and band dispersion.
• To investigate the presence of correlation-driven features such as band renormalization and dispersion anomalies resembling those in cuprates.

Proposed method

• Molecular beam epitaxy (MBE) was used to grow high-quality La0.8Sr0.2NiO2 thin films on single-crystal substrates.
• In situ atomic-hydrogen reduction was applied to fully convert the perovskite-like precursor phase into the infinite-layer phase.
• Angle-resolved photoemission spectroscopy (ARPES) was performed at cryogenic temperatures to probe the momentum-resolved electronic structure.
• The experimental data were compared with density functional theory (DFT) calculations to validate the Fermi surface topology and band dispersion.
• Band renormalization and dispersion anomalies were analyzed by examining the effective mass and energy-dependent dispersion features.
• The 3D nature of the Fermi surface was confirmed by measuring along the k_z direction, revealing evolution from hole-like to electron-like character.

Experimental results

Research questions

• RQ1 What is the true momentum-resolved Fermi surface topology of superconducting infinite-layer lanthanum nickelates?
• RQ2 To what extent do the Ni-dx²−y²-derived bands exhibit strong electron correlations, as indicated by mass enhancement?
• RQ3 Are there dispersion anomalies—such as kinks or waterfall features—similar to those observed in cuprate superconductors?
• RQ4 How does the 3D character of the electronic structure, particularly the electron pocket at the Brillouin zone corner, influence superconducting pairing?
• RQ5 How well do DFT calculations reproduce the experimental electronic structure, and what corrections are needed to account for many-body effects?

Key findings

• The measured Fermi surface exhibits a large, hole-like Ni-dx²−y²-derived sheet that evolves into an electron-like character along the k_z direction, confirming a 3D Fermi surface topology.
• The Ni-dx²−y²-derived bands show a significant mass enhancement with m*/m_DFT ≈ 2–3, indicating strong electron correlations.
• A three-dimensional electron pocket centered at the Brillouin zone corner is observed, consistent with theoretical predictions.
• The Ni-dx²−y² bands display a dispersion anomaly at higher binding energy, resembling the kink and waterfall features seen in cuprates.
• The 3D electron band shows negligible band renormalization, suggesting weaker correlations in this portion of the Fermi surface.
• The overall agreement between ARPES data and DFT calculations validates the electronic structure model while highlighting the importance of many-body effects in the dx²−y²-derived states.