Photoemission Spectroscopy Reveals Electronic Origin of Density Waves in La NiO Trilayers

Researchers are striving to understand the complex origins of high-temperature superconductivity in Ruddlesden-Popper nickelates, a relatively new area of condensed matter physics. Jiangang Yang, Jun Zhan, and Taimin Miao, from the Beijing National Laboratory for Condensed Matter Physics, alongside Mengwu Huo et al, have now shed light on the electronic basis of density wave orders within these materials. Their work, focusing on the trilayer nickelate LaNiO₂, presents the first experimental evidence of band splitting caused by interlayer coupling and reveals detailed density wave gaps across Fermi surfaces. This is significant because it identifies a key mechanism, mirror-selective Fermi surface nesting, driving interlayer antiferromagnetic spin density waves, and confirms the crucial role of nickel-3d orbitals in the material’s low-energy behaviour, offering a fundamental step towards unlocking the secrets of superconductivity in this family of compounds.

The research team combined high-resolution angle-resolved photoemission spectroscopy with tight-binding model simulation to investigate the electronic structure of La4Ni3O10, a representative trilayer nickelate.

This approach allowed for detailed analysis of the material’s behaviour and the underlying mechanisms driving its superconducting properties. The study provides the first experimental evidence of band splitting caused by interlayer coupling, a key characteristic of these multi-layered nickelates. Researchers were able to resolve momentum-dependent density wave gap structures across all Fermi surfaces, offering unprecedented insight into the material’s electronic behaviour.
This detailed mapping of the Fermi surface is essential for understanding the complex interplay of electronic correlations and magnetic interactions. Findings from the work identify mirror-selective Fermi surface nesting as the origin of the interlayer antiferromagnetic spin density wave. This discovery establishes a direct link between the material’s electronic structure and its magnetic ground state, clarifying how these two properties are intertwined.

Furthermore, the research demonstrates the dominant role of Ni-3dz2 orbitals in the low-energy physics of La4Ni3O10, highlighting the importance of these orbitals in mediating the material’s electronic behaviour. Experiments show that the observed spin density wave order is driven by interlayer interactions mediated by the dz2 orbitals.

This understanding of the orbital-selective physics is crucial for controlling and enhancing superconductivity in these materials. These results establish a fundamental framework for comprehending magnetic interactions and the high-temperature superconductivity mechanism within the Ruddlesden-Popper nickelate family, potentially paving the way for future advancements in superconducting materials.

Crystalline growth, structural characterisation and spectroscopic measurements of La4Ni3O10 were performed

Scientists grew high-quality single crystals of trilayer nickelate La4Ni3O10 using a high-pressure floating zone method, subsequently verifying their structure with X-ray diffraction analysis. Transport and magnetic susceptibility measurements were then performed on these crystals to characterise their fundamental properties.

The study pioneered the use of synchrotron-based angle-resolved photoemission spectroscopy at the BL03U beamline of the Shanghai Synchrotron Radiation Facility, employing a hemispherical electron energy analyser DA30L (Scienta-Omicron) with an energy resolution of 10, 15 meV. To enhance resolution, high-resolution ARPES measurements were also conducted using a lab-based system equipped with a 6.994 eV vacuum-ultra-violet laser and another DA30L analyser, achieving an energy resolution of 2 meV and angular resolution of 0.2 degrees.

Momentum coverage was increased by applying a bias voltage to the sample during ARPES measurements. All samples underwent in situ cleavage at 20 K within an ultrahigh vacuum environment, maintaining a base pressure below 5x 10−11 mbar. Researchers carefully referenced the Fermi level by measuring a clean, electrically connected polycrystalline gold sample.

Data processing was completed using Igor Pro 8.02 software, and the team ensured full transparency by making all data necessary to support their conclusions available within the published article. Raw data generated during the research are accessible upon request from the corresponding authors, alongside the tight-binding calculation codes used in the study. This methodological approach enabled the identification of band splitting induced by interlayer coupling and the resolution of momentum-dependent density wave gap structures along the Fermi surfaces, ultimately revealing the origin of the interlayer antiferromagnetic spin density wave.

Interlayer Coupling and Fermi Surface Nesting Drive Magnetic Order in La4Ni3O10 as revealed by resonant inelastic x-ray scattering

Scientists have discovered crucial details regarding the electronic structure of La₄Ni₃O₁₀, a trilayer Ruddlesden-Popper nickelate, providing fundamental insights into high-temperature superconductivity. The research team combined high-resolution angle-resolved photoemission spectroscopy with tight-binding model simulations to investigate the material’s properties.

Experiments revealed, for the first time, band splitting induced by interlayer coupling, a phenomenon where interactions between layers alter the energy levels of electrons. Measurements further resolved momentum-dependent density wave gap structures along all Fermi surfaces, mapping the energy gaps arising from the density wave order across the material’s electronic landscape.

Data shows a clear link between mirror-selective Fermi surface nesting and the origin of the interlayer antiferromagnetic spin density wave, indicating how electrons interact to create magnetic order. The team identified that Ni-3d orbitals play a dominant role in the low-energy physics of La₄Ni₃O₁₀, highlighting the importance of these electron orbitals in determining the material’s behaviour.

Results demonstrate that the observed interlayer antiferromagnetic spin density wave is driven by Fermi surface scattering between bands possessing opposite mirror parity. Specifically, the research confirms the crucial role of dz²-mediated interlayer interactions in establishing this spin density wave state. The study measured a metal-to-metal transition at approximately 140 K, accompanied by a change in magnetic structure, which is progressively suppressed under pressure.

Interlayer antiferromagnetic order from Fermi surface nesting in La4Ni3O10 is reported

Scientists have uncovered crucial details regarding the electronic structure of La₄Ni₃O₁₀, a trilayer Ruddlesden-Popper nickelate, advancing the understanding of high-temperature superconductivity in this material family. Combining high-resolution angle-resolved photoemission spectroscopy with tight-binding model simulations, researchers have demonstrated the existence of band splitting caused by interlayer coupling and identified momentum-dependent density wave gap structures across the Fermi surfaces.

These observations pinpoint mirror-selective Fermi surface nesting as the origin of an interlayer antiferromagnetic spin density wave, highlighting the significant role of nickel-3d orbitals in the material’s low-energy physics. This work establishes a fundamental framework for comprehending magnetic interactions and potentially high-temperature superconductivity within the broader Ruddlesden-Popper nickelate family.

The identified interlayer antiferromagnetic spin density wave suggests a mechanism whereby suppression of this static magnetic order via high pressure could induce strong interlayer spin fluctuations, potentially facilitating superconducting pairing. Authors acknowledge that while their findings offer insights into the complex magnetic interactions, further investigation is needed to fully elucidate the pairing mechanisms at play. Future research could extend this framework to other Ruddlesden-Popper nickelates to explore the universality of these observed phenomena and refine the understanding of unconventional superconductivity achieved through tuning of 3D interlayer magnetic coupling.